Flight Model in ﬁnal preparation for RFC test at ESTEC

Page

Introduction 5

Mission and System 7

Satellite 13

Payload and Applications 19

• Radar Imagery 20

• Oceans, Coastal Zones and Land 28

• Atmosphere 34

• Altimetry 42

Ground Segment 49

Overall Development and Verification 53

C o n t e n t s 3

Contents

Flight Model in final preparation for RFC test at ESTEC

4

Introduction

I n t r o d u c t i o n 5

Throughout history, our planet Earth hasundergone changes to its physicalcharacteristics caused by natural evolutionary activities.

Recently, however, it has been recognised thatthe changes in our environment may also beaffected adversely by human activities.Growing population and economicdevelopment are placing heavier andexpanding demands and stresses upon thefinite resources of the Earth’s system. There isalso an increased awareness of the human andeconomic significance of the natural variabilityof the environment, particularly with regard tothe effects of extreme events – manifestedthrough natural disasters such as floods and earthquakes.

This growing concern has resulted ininternational agreements that future humanactivities and developments must minimiseany type of environmental damage.

In order to monitor environmental changes andto support studies of the effects andinterrelations of the various natural and man-made contributors to the global climatechange, systematic observations of the Earthhave to be performed. These observations needto be made both on a global scale for world-wide environmental needs, and on a regionalscale to support local environmental issues anddevelopments. They have to be performed overtime periods long enough to allow seasonalvariations to be considered, and have tocomprise a number of different geophysical,biophysical and chemical measurements.

Modern technological developments haveprovided remote sensing satellites as a primarymeans of performing such global research. The European contribution to the Earthobservation programme is the ENVISATsystem, an advanced environmental satellitedesigned to provide measurements of theatmosphere, oceans, land and the polar regions.

After an overall development period in theorder of ten years, the ENVISAT system hasnow successfully finished its final testing and is ready to be launched.

Once spaceborne, the ENVISAT mission willprovide, in a continuation and extension of theERS programme, information from a uniquecombination of ten multi-disciplinary sensors,resulting in unprecedented opportunities inenvironmental monitoring and operationalEarth observation.

By the development of the ENVISAT system,the European space community hassuccessfully managed the challenges of ahighly demanding programme, confirming itsleading role in Earth observation.

6

Ocean

- Ocean colour- Sea surface temperatures- Surface topography- Turbidity- Wave characteristics- Marine geoid

Atmosphere

- Clouds- Humidity- Radiative Fluxes- Temperature- Trace Gases- Aerosols

Ice

- Extent and type- Snow cover- Topography- Temperature

Land

- Surface temperatures- Vegetation characteristics- Surface elevation- Earth crust and interior

M i s s i o n a n d S y s t e m 7

To monitor and study our environment on aglobal scale, polar orbiting remote sensingsatellites offer unique features:

• complete Earth coverage,

• high revisiting rate,

• continuity of measurements over seasonsand years,

• stable and highly repeatable measurements.

With this background the ENVISAT missionhas been defined to endow Europe withenhanced capability to:

• monitor and study the Earth’s environmentand climate changes,

• manage and monitor the Earth’s resources,

• develop a better understanding of thestructure and dynamics of the Earth’s crustand interior.

The system will provide:

• continuity of the observations started withthe ERS satellites,

• enhancement of the ERS missions, notablyits ice and ocean missions,

• extension of the contributions toenvironmental studies in particular in thearea of atmosphere chemistry and marinebiology.

The mission will serve both global as well asregional monitoring objectives. Continuous and coherent global data sets willbe made available, for example, for:

• scientific and application communities tounderstand more fully the climaticprocesses and to improve climate models,

• medium and long term weather forecasts,

• studying of tectonic motions and seismic phenomena (in conjunction with SARinterferometry).

Mission and System

The regional data sets will support the scienceand application user communities with avariety of objectives, such as:

• coastal process and pollution monitoring,

• ship traffic routing,

• agriculture and large scale vegetationmonitoring,

• hazard monitoring.

Depending on their application the data will beavailable in nearly real-time, or as off-lineproducts in the order of days to weeks aftersensing.

To meet the mission objectives the orbit forENVISAT will be a high inclination, sunsynchronous, near circular orbit in the altituderange between 780 km and 820 km. The localmean solar time at the descending node will be10:00 a.m.

The orbit maintenance strategy ensures that the deviation of the actual ground track fromthe nominal one is kept below 1 km and thatthe mean local nodal crossing time matches the nominal one to better than 1 minute.

The ENVISAT operational design facilitates theacquisition of measurement data from anypoint on the Earth’s surface and atmospherewithin the coverage of its sensors.

Although the repeat cycle of the ENVISATReference Orbit is 35 days, it provides for mostsensors a complete coverage of the globewithin one to three days. The regions of higherlatitude will be covered even more frequently.Because of their measurement principle, inparticular their narrow field of view, theinstruments DORIS, MWR and RA-2 do notprovide real global coverage, but span a tightmatrix of measurements over the globe.

The ENVISAT reference scenario for satellite-to-ground communication employs variousground stations (Kiruna, Fucino, Svalbard) andthe ESA Data Relay Satellite ARTEMIS. In addition, further national stations will be involved.

The satellite will be launched from the KourouSpace Centre in French Guyana by an Ariane 5launch vehicle.

8

ENVISAT satellite configuration

Instrument contribution to ENVISAT measurement objectives

The system needed to achieve themission objectives requires twomajor components:

• the Satellite and

• the Ground Segment.

Additionally, the ARTEMIS DataRelay Satellite system will be usedfor communication to ground.

To meet the mission requirementsa coherent, multidisciplinary setof sensors has been selected, eachcontributing with its distinctmeasurement performance invarious ways to the mission,as well as providing synergybetween the scientific disciplines, thusmaking the total payload complement morethan just the sum of the instruments.

The ENVISAT Satellite comprises a set of sevenESA Developed Instruments:

• Advanced Synthetic Aperture Radar(ASAR),

• Medium Resolution Imaging Spectrometer(MERIS),

• Radar Altimeter 2 (RA-2),

• Microwave Radiometer (MWR),

• Laser Retro-Reflector (LR),

• Global Ozone Monitoring by Occultation ofStars (GOMOS),

• Michelson Interferometer for PassiveAtmospheric Sounding (MIPAS).

They are supported by three complementaryAnnouncement of Opportunity Instruments:

• Advanced Along Track ScanningRadiometer (AATSR),

• Doppler Orbitography andRadiopositioning Integrated by Satellite(DORIS),

Atmosphere

CloudsHumidity

Radiative FluxesTemperatureTrace Gases

Aerosols

Land

Surface TemperatureVegetation CharacteristicsSurface Elevation

Ocean

Ocean ColourSea Surface TemperatureSurface Topography

TurbidityWave Characteristics

Marine Geoid

Ice

ExtentSnow CoverTopographyTemperature

Instruments

Disciplines

ASA

R

GO

MO

S

RA

-2

MER

IS

MIP

AS

MW

R

SCIA

MA

CH

Y

DO

RIS

AA

TSR

LR

M i s s i o n a n d S y s t e m


• Scanning Imaging Absorption Spectrometerfor Atmospheric Cartography(SCIAMACHY).

These instruments operate over a wide band of the electromagnetic spectrum, ranging fromcentimetre waves to the ultraviolet.

The Polar Platform is made up of two majorassemblies:

• the Service Module (SM) whichaccommodates most of the satellite supportsubsystems such as:

– power generation, storage anddistribution,

– Attitude and Orbit Control System(AOCS),

– communication on S-Band,– support structure and launcher interface,

• the Payload Module (PLM) on which theinstruments and the payload dedicatedsupport subsystems are mounted:

– instrument control,– payload data storage,– communication on X- and Ka-Band,– power distribution,– support structure.

ENVISAT in ESTEC Hydra Facility

1000

100

10

1

0.1

0.01

microwaves infrared ultra-violet

Frequency (Hz) 109 1010 1011 1012 1013 1014 1015

Band L S C X Ku K Ka

Ionosphere

H2OH2O

H2O

H2O

O2

O2CO2

CO2CO2

H2O

H2O

O3

O3

ASAR

GOMOS

MERIS

MIPAS

MWR

RA-2

LR

AATSR

DORIS

SCIAMACHY

1 µm10 µm100 µm0.1 cm 0.1 µm1 cm10 cm100 cmWavelength

Measurement spectrum of the ENVISAT instruments

S-Band

Ka-Band

ESOCFOCC

ESRIN PDS

Kiruna FOS & PDS

Users

Ka-BandX-Band

10

For the transmission of measurement data toground, two alternative scenarios are defined:

• the baseline scenario with acquisition via X-and Ka-Band links,

• a back-up X-Band scenario wheretransmission will be performed on X-Band only.

Within both scenarios the global as well asregional mission objectives will be served.

The requirement for global coverage impliesthe use of onboard data storage in bothscenarios. ENVISAT is equipped with twoSolid State Recorders, each with a capacity of70 Gbit, and a 30 Gbit tape recorder as a backup. They allow recording of the 4.5 Mbpscomposite data stream of the low data rateinstruments over a complete orbit, as well asrecording MERIS full resolution data or ASARimage mode data for dedicated regionalobservations. The data will also be downlinkedvia ARTEMIS or directly to the ground stationsdepending on the scenario.

To downlink the stored data within theminimum ground contact time, playback ratesof 50 Mbps and 100 Mbps are provided. For thedownlink of the different categories ofmeasurement data, the following channelstransmitting 100 Mbps each, are available:

• one X-Band channel used for recorderdumps and real-time transmission,

• one X-Band channel for ASAR high ratemeasurement data,

• in case of transmission via ARTEMIS twoKa-Band channels with the same allocationas for the X-Band.

The Ground Segment provides the means andresources to manage and control the mission,to receive and process the data produced bythe instruments, and to disseminate andarchive the generated products. Furthermore, itwill provide a single interface to the users toallow optimum utilisation of system resourcesin line with user needs.

The Ground Segment can be split into twomajor elements:

• the Flight Operation Segment (FOS),

• the Payload Data Segment (PDS).

The FOS is composed of the Flight OperationsControl Centre (FOCC), located at ESOCDarmstadt (Germany), and the associatedcommand and control stations. It providescontrol of the satellite through all missionphases:

• satellite operation planning based upon theobservation plans prepared at the PayloadData Control Centre (PDCC),

• mission planning interface with ARTEMIS,

• command and control of the satellite, up-loading of operation schedules on adaily basis via the TT&C station at Kiruna-Salmijärvi (north Sweden).

Furthermore, the FOCC will support:

• satellite configuration and performance monitoring,

• software maintenance for PPF and payload elements,

• orbit prediction, restitution andmaintenance.

Data flow between Satellite and Ground Segment

M i s s i o n a n d S y s t e m


Satellite command and control will nominallybe performed using the S-Band via the KirunaGround Station. During Launch and EarlyOrbit Phase (LEOP), the Kiruna Station will becomplemented by a LEOP TT&C stationnetwork providing coverage of critical events.

The PDS comprises all those elements whichare related to payload data acquisition,processing and archiving, and those concerningthe user interfaces and services. The PDS willthus provide:

• all payload data acquisition for the global mission,

• regional data acquisition performed byESA stations,

• processing and delivery of ESA FastDelivery Products,

• data archiving, processing and delivery ofESA off line products with support ofProcessing and Archiving Centres (PACs),

• interfaces with national and foreign stationsacquiring regional data,

• interfaces to the user from order handlingto product delivery.

The PDS centres and stations will be co-ordinated by the PDCC located at ESRIN,Frascati, Italy. The PDCC will interface with theFOCC for all mission planning activities.

The PDS ESA stations include: a Payload DataHandling Station (PDHS-K), located at Kiruna-Salmijärvi, providing X-Band data reception;the PDHS-E located at ESRIN, receiving via aUser Earth Terminal (UET) data relayed byARTEMIS; and a Payload Data AcquisitionStation (PDAS), located at Fucino (Italy),receiving X-Band data. For those orbits whichare out of the visibility of the Kiruna PDHSand when ARTEMIS is not available, a highlatitude receiving station at Svalbard will beused to acquire payload data dumps.

Launch

Injection

L7 stageSeparation

Solar arrayprimary deployment

Solar arraysecondary deployment

Wheel controlledfine pointing mode

ASAR instrumentdeployment

Attitude acquisition

Solar arrayMEGS release

Solar arrayrotation

Kourou

ENVISAT Launch & Early Orbit Phase (LEOP) sequence

Main Control Room at the FOCC

12

Flight Model after Service and Payload Module integration at ESTEC

S a t e l l i t e 13

The Payload Module (PLM) consists of thePayload Carrier (PLC) and the PayloadEquipment Bay (PEB). The PLC providesmounting surfaces measuring 6.4 m x 2.75 mfor the payload instruments and associatedelectronics. The payload dedicated supportsystems are mounted in the PEB. The payloadsupport functions include instrument controland data handling, X-Band and Ka-Bandcommunications sub-systems, powerdistribution, support structure and thermal control.

Satellite

The ENVISAT satellite is composed of twomajor elements: the Polar Platform and theinstruments constituting the Earth observation payload.

A major driver for the overall satelliteconfiguration has been the need to maximisethe payload instrument mounting area and tomeet their viewing requirements, whilststaying within the constraints of the Ariane 5fairing and interfaces.

The Polar Platform configuration conceptprovides a large modular constructioncomprising two major assemblies, the ServiceModule and the Payload Module. The ServiceModule provides the basic satellite functions ofpower generation, storage and distribution,Attitude and Orbit Control, S-Band Telemetryand Telecommand Communication, and data handling for the overall satellite control functions.

Satellite – major components

DRS Antenna

StarSensors

PropulsionModule

Solar Array

ServiceModule

PayloadCarrier

Payload Equipment Bay

14

Spacecraft

Spacecraft Appendages AppendagesDimensions Stowed Fully Deployed

Height: 10.0 m 25.0 m

Depth: 4.0 m 7.0 m

Width: 4.0 m 10.0 m

Solar Array: 14.0 m x 5.0 m

Satellite Mass: 8050 kg (at launch)

Solar Array

Output Power: 6600 W (end of life)

Design Lifetime: 5 years

Orbit: Near-polar sun-synchronous

Mean Altitude: 800 km

Local Solar Time: 10:00 hr (descending node)

Repeat cycle: 35 days

Satellite Characteristics

S a t e l l i t e

Payload

Instrument Mass: 2050 kg

Instrument Power: 1930 W average, 3000 W peak

Recording 2 solid state recorders with 70 Gbits storage capacity each, plusCapabilities: 1 tape recorder with 30 Gbits storage capacity

Downlink 2 Ka-Band links to European Data Relay Satellite, and 2 X-BandInterfaces: links direct to ground, both at 50 Mbps or 100 Mbps


Flight Model in preparation for acoustic test in LEAF, ESTEC

Flight Model PLM in ESA Thermal Vacuum Chamber

16

S a t e l l i t e

Service Module

The Service Module (SM), developed byAstrium SAS (F), is based on the concept anddesign of the SPOT-4 Service Module with anumber of important new developments,particularly in the area of mechanical design.

These include:

• an enlarged equipment module consistingof a box shaped structure made ofaluminium honeycomb panels fabricatedaround a central carbon fibre compositecone, which constitutes the primarystructure. The majority of the subsystemequipment, including additional Attitudeand Orbit Control System actuators to copewith the increased size of ENVISATcompared to SPOT, are located inside thismodule. At the lower end of the module,the cone provides a means for interfacingwith the ARIANE 5 launch vehicle adaptor.The upper end of the cone provides theinterface to the propulsion module and inturn the Payload Module central cylinder,

• an enlarged battery compartment allowing installation of the required eight 40 AhNickel-Cadmium batteries,

• the propulsion module comprising four propellant tanks which provide ENVISAT with a fuel capacity of 300 kg of hydrazine.

The single wing Solar Array is a particularlyimportant new development. The arraycomprises a primary deployment mechanismand arm, plus a set of 14 deployable rigidpanels capable of providing 6.6 kW at end oflife. This array is based on the rigid paneltechnology already flown on EURECA.

The digital Dual Mode Transponder is anothernew development. It provides a 2000 bpsforward and 4096 bps return S-Band linkcapability. Ranging and range ratemeasurements are performed by groundstations on the range signals transmitted by thetransponders in either coherent or non-coherent modes.

The Attitude and Orbit Control System consistsof Star Trackers and Gyros providing theprimary measurement system, together withSun Sensors and Earth Sensors. The actuatorsare reaction wheels for nominal operation, andthrusters for coarse pointing and orbitmanoeuvering/correction.

The attitude and orbit control, reaction control,power distribution, and data storage andhandling systems extensively re-use SPOTdeveloped hardware, either unmodified or withminor modification. In addition, the SM on-board and ground check-out softwares arere-used with only limited modification.

Flight Model Solar Array (Photography by courtesy of Fokker Space)

Flight Model SM installed in the ESTEC TB/TV test facility


Payload Module

The Payload Module (PLM) comprises thePayload Carrier (PLC) and the PayloadEquipment Bay (PEB). The PLC provides themain structural support for the PEB and theexternally mounted instruments and antennae.In addition, the PLC provides accommodationfor certain equipments which are functionallypart of the Service Module but need to belocated within the Payload Module.

The PEB, developed by Astrium GmbH (D),provides all the necessary functions to supportand control the payload instruments as well asto handle scientific data. The PEBaccommodates the following sub-systems:

• the Payload Management Assembly,comprising the Payload ManagementComputer with its mission specificapplication software and three RemoteTerminal Units constituting the interface forthe monitoring and control of the PEBfunctions and the Payload Instruments,

• the Data Handling subsystem, including:

– the High Speed Mutliplexer (HSM),which can select and assemble theinstrument data into a continuous datastream of up to 50 Mbps for transmissionto ground or 4.5 Mbps for data recording,

– two 70 Gbit solid state recorders, backedup by a 30 Gbit tape recorder, allowingfor intermediate storage of HSM outputdata during periods without directground station coverage,

– the Encoding and Switching Unit, toencode and to switch HSM, recorderplayback, or payload high rate data to thedifferent RF downlink channels,

• the X-Band transmission subsystem, providing three 100 Mbps or 50 Mbpschannels (including one redundant) fordata transmission to ground. It comprisesthe modulators, the Travelling Wave Tubesand their power conditioners for signalamplification, the Output Multiplexer,which combines the three links prior totransmission, and the fixed X-Bandantenna located on the Payload ModuleEarth face,

• the Ka-Band transmission subsystem, providing three 100 Mbps or 50 Mbpschannels (including one redundant) fordata transmission to ground via the ESA’sARTEMIS satellite. It uses similarmodulation and amplification hardware asthe X-Band subsystem, but requires on thezenith face an outboard assembly consistingof a deployable mast and antenna. An Antenna Pointing Mechanism ensuresthat the antenna tracks the Data Relay Satellite,

• the power subsystem, comprising two Power Distribution Units, one for the PEBequipments and the other for theinstruments and the Heater SwitchingUnit, providing power to the PayloadModule Heaters under the control of thePayload Management Computer.

Flight Model PEB undergoing final integration

18

Oil spillage offSpanish coast

Total ozone observed by ERS-2

ERS-1 multi-temporal radarimage of Rügen andVorpommern showing vegetation patterns

ATSR-2 visiblecomposite imageof the state ofColorado

P a y l o a d a n d A p p l i c a t i o n s 19

Payload and Applications

Monitoring a complex system like the Earth’senvironment demands a specific set of multi-disciplinary payload instruments whichcomplement each other. The translation of themission objectives into physical andengineering parameters, which finally have tobe measured, results in a payload comprising10 individual instruments, even when usingstrong selection criteria governed by availablefinancial budget and physical systemconstraints. The comprehensive measurementrequirements with respect to the:

• atmosphere,

• biosphere,

• hydrosphere,

• geosphere,

• cryosphere,

and corresponding distinct physical quantities:

• spatial resolution (global and regional data),

• spectral range and resolution,

• radiometric resolution

will be met by the unique set of two radarinstruments, three spectrometers of differenttypes and measurement characteristics, twodifferent radiometers, broad and narrow band,and the first high-resolution spaceborneinterferometer for long term observation,complemented by two instruments for rangemeasurements.

In accordance with their primary field ofapplication, the ENVISAT payload instrumentscan be categorised into four areas:

• radar imagery performed by ASAR,

• Ocean, Coastal Zone and Land observationsupported by MERIS and AATSR,

• atmospheric measurements performed byGOMOS, MIPAS and SCIAMACHY,

• altimetric mission of RA-2 supported byMWR, LR and DORIS.

Artists view of Envisat

20

Radar Imagery

Advanced Synthetic Aperture Radar(ASAR)

The ASAR is a high-resolution, wide-swathimaging radar instrument that can be usedboth for site specific research and for globalland and ocean monitoring and surveillance.Its main objective is to monitor the Earth’senvironment and to collect information on:

• ocean wave characteristics,

• sea ice extent and motion,

• snow and ice extent,

• surface topography,

• land surface properties,

• surface soil moisture and wetland extent,

• deforestation and extent of desert areas,

• disaster monitoring (flooding, earthquake, etc).

The major advantage of using a SARinstrument for these Earth observation tasks isits capability to take images independent ofweather conditions, cloud coverage and solarillumination. Considering in particularobservations of disasters like floods or

hurricanes, which usually happen in adverseweather conditions, this weather independenceis of vital importance.

Compared to the ERS-1 & 2 Active MicrowaveInstrument (AMI), the ASAR is a significantlyadvanced instrument employing a number ofnew technological developments, where thereplacement of the passive radiator array of theAMI by an active phased array antenna systemusing distributed elements was the mostchallenging one. The resulting improvementsare the capability to provide more than 400 kmwide swath coverage using ScanSARtechniques, and the alternating polarisationfeature allowing scenes to be imagedsimultaneously in vertical (V) and horizontal(H) polarisation.

In nominal operation a radar antenna beamilluminates the ground to one side of thesatellite. Due to the satellite motion and thealong-track (azimuth) beamwidth of theantenna, each target element stays inside theillumination beam for a while. As part of theon-ground signal processing, the complex echosignals received during that time will be addedcoherently. In this way a long antenna issynthesised with the Synthetic Aperture lengthbeing equal to the distance the satellitetravelled during the integration time. The along-track resolution obtainable with this

principle is about half the real antennalength. However, to enhance the

radiometric resolution, multilook azimuthprocessing will be applied on ground,

and consequently the along-trackresolution will be degraded by afactor equal to the look number.

The across-track or range resolutionis a function of the transmitted

radar pulse length. Pulsecompression techniques are

used to improve ASARperformance, taking intoaccount the instrumentpeak power capability.

FlightDirection

405 km

Global MonitoringVV or HH1000 m resolution

AlternatingPolarization VV, HH, VH or HV30 m resolution<100 km swath width(selectable)

100 km

100 km

Wave VV or HH30 m resolution5 km x 5 km vignettes

100 km

Image VV or HH30 m resolution<100 km swath width(selectable)

485 km

Wide Swath VV or HH150 m resolution(using ScanSAR technique)

P a y l o a d a n d A p p l i c a t i o n s

ASAR operation modes


The instrument is designed to operate in thefollowing principal operating modes:

• image,

• wide swath,

• wave,

• alternating polarisation,

• global monitoring.

In image mode the ASAR gathers data fromrelatively narrow swaths (100 km within aviewing area of appr. 485 km) with high spatialresolution (30 m), whereas in wide swath modeusing ScanSAR techniques a much wider stripe(400 km) is imaged with lower spatialresolution (150 m). In wave mode, ASARmeasures the change in radar backscatter fromthe sea surface due to ocean surface waves. In this mode images of 5 km x 5 km are takenover the ocean at a distance of 100 km. The alternating polarisation mode providesimaging of a scene with alternatingpolarisation during transmission and reception.The spatial resolution is equal to that of imagemode. In global monitoring mode a wideswath (400 km) is imaged with 1000 m spatial resolution.

The low data rates in wave and globalmonitoring mode can be recorded continuouslyup to the full orbit. The high rate data modesare operated upon user request. With thecapability of on board recording, the operationof the instrument is independent of theavailability of ground station contact. Theradar images obtained by on-groundprocessing of the ASAR data will allow thegeneration of enhanced products suited toapplications over land surfaces, ocean andcoastal regions, and ice zones.

ASAR is developed under leadership ofAstrium Ltd.. (UK).

≤ 30 m≤ 30 m*

≤ 3.5 dB

up to 100 km

≥ 26 dB≥ 18 dB

≥ 18 dB≥ 17 dB

≤ 1.9 dB

5.331 GHz

1650 to 2100 Hz

up to 16 MHz

10 m x 1.3 m

≤ 100 Mbit/s

817 kg

1322 W

Instrument Parameters

Image WideSwath

AlternatingPolarization

Wave GlobalMonitoring

≤ 150 m≤ 150 m

≤ 1.54 dB

≥ 400 km

≥ 25 dB≥ 20.3 dB

≥ 20.3 dB≥ 17 dB

≤ 1.56 dB

Up to30 min/orbit

≤ 100 Mbit/s

1161 W

≤ 30 m≤ 30 m*

≤ 2 dB

5 km vignette

≥ 30 dB≥ 22.6 dB

≥ 22.6 dB≥ 21.5 dB

≤ 2.1 dB

Rest of orbit

0.9 Mbit/s

400 W

≤ 1000 m≤ 1000 m

≤ 1.5 dB

≥ 400 km

≥ 25 dB≥ 24 dB

≥ 24 dB≥ 17 dB

≤ 1.82 dB

0.9 Mbit/s

601 W

Spatial Resolution along-track across-track

Radiometric Resolution

Swath Width

Ambiguity Ratio (Point) along-track across-track

Ambiguity Ratio (Dist.) along-track across-track

Radiometric Accuracy

Centre Frequency

Pulse Repet. Frequ.

Chirp Bandwidth

Antenna Size

Operation

Data Rate

Mass

Power

≤ 30 m≤ 30 m

≤ 1.54 dB

up to 100 km

≥ 25 dB≥ 30 dB

≥ 26.6 dB≥ 17 dB

≤ 1.5 dB

≤ 100 Mbit/s

1386 W

* slightly worse for near swath

ASAR performance and budget data

ASAR antenna

22

Radar Image Principle

The signal from the synthetic aperture radarcan be exploited to produce an image. The radar image differs substantially from anoptical image: it is, in reality, a map of apparentradar backscattering (coded as different greylevels) which not only depends on the targetreflectivity at microwave wavelengths, but alsoon the viewing geometry.

One additional salient feature of a microwaveimage – which makes it different from opticalimages we are used to – is that the incoming‘light’ (in this case, the ‘received echo’ of theradar signal) is a monochromatic coherentlight. As a consequence, the image appears‘speckled’ (see SAR single look image). To reduce this effect, several images areincoherently combined as if they correspondedto different ‘looks’ of the same scene. The resulting improvement in imageinterpretability is shown in the SAR multi look image.

New ASAR Features

Among the many new features that ASARpresents, compared not only to ERS-1 & 2 butto any other spaceborne flying SAR, is thecapability to transmit and receive signals withdifferent polarisation (either vertical orhorizontal). Because any given target respondsin a specific way when illuminated with adifferent polarisation (see example in thefigure), this technique greatly increases thecapability of applications like classification,agriculture and forestry.

ASAR will also be characterised by thecapability to image large areas (up to 400 kmswath width), thus significantly improving therevisiting time compared to ERS-1 & 2.

SAR single look image

SAR alternating polarisation imagesLeft: SAR transmit H, receive H and V

Right: transmit H, receive V(Images by courtesy of SARMAP S.A. (CH))


SAR multi look image

Interferogram from ERS Tandem Mission of part of theVatnajokull Glacier, Iceland, May 1997(Image by courtesy of H. Rott, Institut für Meteorologieund Geophysik, Innsbruck, Austria)

Digital Elevation Model of the Etna volcano built from ERS SAR data


Digital Elevation Models

Digital Elevation Models (DEM) are three dimensional maps of a terrain surface.The INSAR technique provides an excellenttool to derive large scale DEMs.

Digital Elevation Models (such as the one ofEtna volcano shown here) can be constructedfrom interferometry data, with a maximumerror in the order of 5 to 20 m, depending onthe terrain topography.

Interferometry

A powerful technique for application of theSynthetic Aperture Radar is that of SARInterferometry, or INSAR. The INSARtechnique exploits the phase information of theradar signal backscattered from the Earth’ssurface. By comparing the phase differencebetween two images of the same scene, takenby the same sensor in two subsequent passes, aphase difference image known as‘interferogram’ is built.

The interferogram (right) shows, in the upper central part, a major depression caused by a sub-glacial volcanic eruption (see photographs below).

24


Subsidence by DifferentialInterferometry

By comparing interferograms taken at differenttimes, the displacement of points on theground can be estimated. This technique isextremely sensitive and displacements in theorder of millimeters can be measured from space.

The image shows the mean velocity field ofParis from 1992 to 1999. The map has beenderived from 64 ERS images and thesubsidence rate is shown from zero (blue tolight green) up to - 4 mm/year (red). More than 100 permanent scatterers per squarekilometers have been identified and used toseparate motion, elevation and to correct foratmospheric phase contributions.

Subsidence measured over Paris(Image by courtesy of Politecnico di Milano–T.R.E.(I))

0

mm/yr

- 4

Image B: SAR differential interferogram obtained from ERS SAR

Image A: Theoretical deformation model

Earthquake between Istanbul and the lake of Sapanca Earthquake

SAR interferometry can be used to quantify thedislocation produced by an earthquake.Basically, two interferograms have to becompared, therefore three measurements areneeded to derive the spatial displacements.

In the case of an earthquake which occurred inTurkey, a theoretical deformation model,derived from geophysical data, was used torecompute the terrain movement and display itas fringes, Image A.

The ERS SAR-derived phase interferogram,Image B, compares very closely with themodel.

The geophysical interpretation of the model isthat the rupture occurred along an east-westfault, causing a predominantly horizontalmovement (right-lateral strike).

In the interferogram (Image B), each fringecorresponds to a ground displacement of 28 mm. By counting the number of fringes, one can calculate the co-seismic deformation of about 80 cm.

Damage Assessment

Besides SAR intensity images andinterferograms so called coherence productscan be generated from SAR data. These coherence products show theinterferometric correlation which is a measureof the variance of the phase coherence betweentwo interferograms.

In terms of coherence imagery, differentground cover types manifest different degreesof coherence. Bare or sparsely vegetated soilhas a high degree of coherence as there is littleor no change in the scatterer propertiesbetween the two acquisitions. Forested areas,on the other hand, show a low degree ofcoherence, as the elementary scatterer (i.e.leaves) in each pixel move between the twoacquisitions, mainly due to wind and, hence,lead to de-correlation in the imagery. This factcan be exploited to discriminate between forestand non-forest vegetation.

Results of the exploitation of the coherenceproduct over the forest of Haguenau, 30 kmnorth of Strasbourg, are illustrated in theimages alongside. These were derived from theprocessing of two coherence products derivedfrom two ERS-1 & 2 tandem pairs acquiredbefore the storm, on 31 October and 1 November 1999 (a), and after the storm, on 9 and 10 January 2000 (b). In these productsareas with high coherence are shown inorange-red, areas with less coherence (e.g.forests) in green. Thus, the coherence productallows one to separate forest/non-forest areas.The coherence product realised after the stormshows a strong increase of the coherence levelwithin forested areas (b). A ‘damage’ imagewas produced based on the ratio of the twocoherences, and averaged SAR intensity (c). In the ‘damage’ image composite, pink tonesprovide an estimate of the level of the damage.In this case, a level of damage of 50% had beenreported by the forestry service whichcorresponds statistically to the increase ofcoherence over the area.

SAR image of Haguenau forest before storm

SAR image of Haguenau forest after storm

‘Damage’ image of Haguenau forest

(Images by courtesy of Service Régional de Traitementd’Image et de Télédétection (F))

(a)

(b)

(c)


Devastated forest

26


Classification

A combination of multi-temporal intensityimages with coherence images allows a furtherdiscrimination of different type of land use.

In the illustrated example, using two coherenceimage pairs – one pair prior to the storm (4/5April 1999) and one pair after the storm (9/10January 2000) – a change within forested areasfrom low coherence to high coherence isindicative of forest damage. Using thecoherence combined with the backscatter data,a supervised classification was carried out toidentify forest areas damaged, as well as theother cover types in the scene. The classifiedimage overlaid on a DEM, generated usingInSAR techniques, is shown in the figure.

Land classification in the vicinity of Bern using SAR data(Image by courtesy of SARMAP S.A. (CH))

Ice Classification

Combining and comparing SAR imagesacquired over the same area at different timesallows surface characterisations ( type andvariation). The multi-temporal image, figure ofIceland left, was obtained by combining threeimages acquired over different passes. This image was produced with the followingcolour assignment: the blue colour for latewinter 1996, green for mid summer 1997, andred for late summer 1997.

In these mosaics, the glaciers are the dominantfeatures in terms of temporal variability.The largest ice cap is Vatnajoekull, covering8300 sq. km in area. This plateau, dark blue inthe image, feeds ice in about 40 outlet glaciers.During summer, this plateau is covered withwet snow of low radar reflectivity. The purplecolour identifies snow retreat, during latesummer, in the mountains of northern Iceland.

Iceland multi-temporal composite ERS SAR image(Image by courtesy of H. Rott, Univerität of Innsbruck (A))


Sea Ice NavigationRadar extracted sea-ice information can satisfyoperational needs for navigation, offshoreoperations and weather forecasting.

The use of the wide swath mode (400 km wide)provided by ASAR as stripe products up to4000 km long, will offer the possibility ofmonitoring large areas with frequent revisits.

Radar images will be provided to users in nearreal time to support, for example, icebreakeroperations and to assist in optimising vesselroutes.

Floods

Floods are among the most severe risks tohuman lives and properties. The forecastand simulation of floods is essential forplanning and operation of civil protectionmeasures (e.g. dams, reservoirs) and forearly flood warning (evacuationmanagement). Considering that 85% ofcivil protection measures taken by ECMember States are concerned with floods(EC Report Task Force Water, 1996), theeconomic importance of flood forecastingbecomes clear.

The SAR can monitor floods in real timeas illustrated in the example image. The red area around the lake representsflooded land and agricultural fields.

Flooding in Poyand Lake, central China, imaged by fusionof ERS SAR and Landsat-5 TM data

Image of the Walgreen coast of Antarctica, acquired by ERS SAR and processed by the ASAR processor to simulate 150 metres resolution

28

Oceans, Coastal Zones and Land

Medium Resolution ImagingSpectrometer (MERIS)

The Medium Resolution Imaging Spectrometeraddresses the needs of three disciplines,primarily oceanographic and secondarilyatmospheric and land observations. MERIS,complemented by the RA-2 and AATSR,provides a unique synergistic mission forbio/geophysical characterisation of the oceansand coastal zones, and thus for climate andglobal environment study and monitoring.

MERIS is a push-broom instrument measuringthe solar radiation reflected from the Earth’ssurface and from clouds in the visible and nearinfrared range (390 nm to 1040 nm). The 1150 km wide swath is divided into fivesegments covered by five identical camerashaving corresponding fields of view with aslight overlap between adjacent cameras. Each camera images an across-track stripe ofthe Earth’s surface onto the entrance slit of animaging optical grating spectrometer.This entrance slit is imaged through thespectrometer onto a two-dimensional CCDarray, thus providing spatial and spectralinformation simultaneously.

MERIS features a high degree of flexibility. Fully programmable on-board processingallows the selection of up to 15 differentspectral bands with a bandwidth in the rangebetween 1.25 nm and 30 nm.

The spatial information along-track isdetermined by the push-broom principle viasuccessive read-outs of the CCD-array. Full spatial resolution data, i.e. 250 m at nadir,will be transmitted over coastal zones and landsurfaces. Reduced spatial resolution data,achieved by on-board combination of 4 x 4adjacent pixels across-track and along-trackresulting in a resolution of approximately1000 m at nadir, will be generatedcontinuously.

MERIS Flight Model (Photograph courtesy of Alcatel SI (F))

Sub SatelliteTrack

Nad

ir 8

00 k

m

1150 km

-

Flight Direction


1.25 nm

260 m

Field Swath

390 nm

1040 nm

Storage Zone

Shift Register

Dump Drain

CCD-array schematic


The instrument is optimised for absolute andrelative radiometric performances, featuringregular updating of calibration parametersapplied on-board via dedicated calibrationhardware to achieve long-term stability.

The instrument data will be pre-processed inflight and on ground to provide spectralimages of the Earth, corrected for atmosphericinfluence. The data will be used for thegeneration of large scale maps, e.g. for:

• ocean pigment concentrations,

• coastal water monitoring,

• clouds and water vapour,

• vegetation status and distribution.

MERIS is developed under leadership ofAlcatel Space Industries (F).

Advanced Along Track ScanningRadiometer (AATSR)

The primary scientific objective of the AATSRis to establish continuity of the ATSR-1 and 2data sets of precise Sea Surface Temperature(SST), thereby ensuring the production of aunique 15 year near-continuous data set at thelevels of accuracy required (0.3 K or better) forclimate research and for the community ofoperational as well as scientific users who willhave been established through the ERS-1 & 2missions.

The second objective is to develop and exploitthe science of quantitative remote-sensing ofland surfaces, particularly vegetation, throughuse of the improved visible-wavelength

atmospheric correction that will be achievablewith AATSR’s two angle view. The land andcloud measurement objectives will be metthrough the use of a visible focal planeassembly, which will lead to indications of:

• vegetation biomass,

• vegetation moisture,

• vegetation health and growth stage.

The above parameters will be used to deriveGlobal Vegetation Indices. The visible channelswill also be used to measure cloud parameterslike water/ice discrimination and particle sizedistribution.

500 km

47°

8 km

900 km

Sub SatelliteTrack

-

Flight Direction

MERIS performance and budget data

Spectral RangeSpectral Sampling IntervalSpectral BandsSpectral BandwidthInstrument Field of ViewAbsolute Localisation AccuracySolar Reflectance abs. Accuracy

Measurement Modes

Polarization SensitivityError of Spectral PositionRadiometric Resolution

Dynamic Range

OperationData Rate

MassPower


390...1040 nm1.25 nm15, centre frequencies programmable1.25…30 nm, programmable68.5°, equivalent 1150 km swath< 2000 m< 2%

full resolution: 0.26 km x 0.29 km at nadir reduced resolution: 1 km x 1 km at nadir < 0.5%< 1 nm15 µW/ (m • sr • nm) at 865 nm (10 nm bandwith, reduced resolution) ~ 40 dB

during day time24 Mb/s full resolution,1.6 Mb/s reduced resolution209 kg146 W

2

30

The field of view of the AATSR comprises two500 km-wide curved swaths, with a pixel sizeof 1 km x 1 km at the centre of the nadir swathand 1.5 km x 2 km at the centre of the forwardswath. The two views result from theinstrument’s conical scanning mechanism. Each scan takes a reading from the nadirposition and then sweeps round to a pointaround 900 km along the satellite’s track.Shortly after acquiring the forward view, thesatellite passes over the same spot and takes areading for the nadir view. As the two views ofthe same scene are taken through differentatmospheric path lengths, it is possible tocalculate a correction for the effect ofatmospheric absorption.

This principle of removing atmospheric effectsin Sea Surface Temperature measurements byviewing the sea surface from two angles is thebasis of the family of (A)ATSR instruments.

The SST objectives will be met through the useof thermal infrared channels (centred on1.6 µm, 3.7 µm, 10.7 µm and 12 µm), identicalto those on ATSR-1 & 2, plus the (A)ATSR’sunique two-angle view of the Earth’s surface.

As with the AATSR thermal infrared channels,the measurement philosophy with respect tothe visible channels will be to develop andexploit a capability for making accuratequantitative measurements of radiation fromthe Earth’s surface, using an on-boardcalibration system for basic radiometricaccuracy, and using a two-angle viewingtechnique to obtain accurate atmosphericcorrections.

The most important two visible channels at0.67 µm and 0.87 µm provide measurements ofVegetation Index, the additional channel at 0.55 µm supports the determination of thevegetation state (chlorophyll content).

The AATSR, developed under the leadership ofAstrium Ltd. (UK), is a British/Australiancontribution to the ENVISAT Mission.

AATSR Engineering Model

AATSR performance and budget data


Spectral ChannelsInfraredVisible

Spatial ResolutionRadiometric ResolutionSST AccuracySwath Width

OperationData RateMassPower

1.6 µm, 3.7 µm, 10.8 µm, 12 µm0.55 µm, 0.66 µm, 0.87 µm

1 km x 1 km0.1 Kbetter 0.5 K500 km

continuously over full orbit625 kb/s108 kg86 W



Sea Surface Temperature (SST)

The SST is one of the most stable of several keygeophysical variables which, when determinedglobally, characterise the state of the Earth'satmosphere system. The precise measurementof small changes in SST will provide anindication of quite significant changes inocean/atmosphere heat transfer rates,especially in the tropics. Temperatureanomalies of small amplitude occurring inspecific areas are sometimes associated withmassive atmospheric perturbations, leading towidespread and damaging changes in theglobal weather system.

The ocean is the largest heat reservoir of theglobe. The heat exchange between the oceanand the atmosphere can be derived by themeasurement of the SST. An event such as ‘ElNiño’ can evolve from a SST anomaly of 2-3 K,and therefore the ability to detect early a 10%change of this anomaly field requiresmeasurement accuracy which can only beprovided by the (A)ATSR instruments. Global SST map produced from the ERS ATSR

The Carbon Cycle and Ocean Phytoplankton

MERIS will measure the bio-physicalproperties and chemical composition of theoceans and coastal waters. There remain majoruncertainties about the amount of carbonstored in the ocean and in the biosphere, andabout the fluxes between these reservoirs andthe atmosphere. The ocean phytoplanktonbiomass accounts for about 50% of thebiosphere’s fixing of CO2 throughphotosynthesis. This biological reactionproduces oxygen. It also ‘traps’ atmosphericcarbon dioxide into organic matter, resulting inprimary biomass production. Increase of carbondioxide concentration in the atmosphere resultsin global warming: it is the ‘greenhouse effect’.

In the upper level of open oceans, chlorophyllconcentration is the best index ofphytoplankton abundance. Observing theoceans using specifically selected colour bandsof MERIS will allow precise estimation of thechlorophyll concentration and derivation ofphytoplankton abundance. It will aid analysisof the contribution of phytoplankton in thecarbon-cycle.

Ocean phytoplankton biomass primary production in May 1999, derived from SeaWifs (Image by courtesy of JRC Ispra (I))

Variation of the global primary production in January, March and May 1999, derived from SeaWifs (Image by courtesy of JRC Ispra (I))

0 10 20 30 40 >50g m-2.month-1

32

Water Vapour and Clouds

The amount of water vapour in the atmosphereis an important component of the Earth’sclimate system. It varies considerably inresponse to variations in temperature andhumidity, and acts as a carrier forredistributing energy around the planet. Water vapour has a large radiative effect and isthe most important greenhouse gas. Water, inthe form of clouds, liquid or ice, modifies theradiation reaching the surface and therebystrongly influences surface energy flux. The role of clouds in the climate system is stillpoorly understood. MERIS will routinelymeasure a number of cloud parameters, likecloud type, cloud albedo and cloud top height.This data will be provided to meteorologicalcentres (in near real-time) thus improving ourclimate modelling and weather forecastingcapabilities.

Coastal Water Monitoring

Like their terrestrial peers, fish in the oceanscan be poisoned by their food, in particulartoxic algae.

MERIS will provide near real time data on thecomposition of coastal water. No in situmeasurement could provide such valuableinformation for fishery management.Furthermore, its high resolution and theadaptability of its spectral bands will be ofunequalled value for scientists involved incoastal water studies.

Coastal water concentrations and sea surfacetemperatures, which will be providedrespectively by the MERIS and AATSRinstruments, are very complementaryobservations; in particular, it is well knownthat fish populations concentrate nearbythermal water fronts.

ATSR instrument image (Courtesy of RAL (UK))

From left to right: True colour composite image, chlorophyll concentration and sea surface temperature image in the Skagerrak region (Denmark)

(Images by courtesy of Plymouth Marine Laboratory (UK))



Vegetation and Biomass

In 1997, most of the world’s countries gatheredin Kyoto agreed on the need to reducegreenhouse gas emissions. Because plants andtrees are both sinks and sources of carbondioxide, the monitoring of our biologicalresources remains crucial.

MERIS, with its large field of view combinedwith the proper selection of spectral bands, willallow regular observation of the world’slandmasses.

This global view of our forest and vegetationwill be complemented with high-resolutionexamination of particular areas, using theMERIS full resolution mode. This will help usto control and regulate deforestation, tomonitor fire damage and more generally, tohelp protect the Earth.

Biomass will be estimated from vegetationindices provided by both MERIS and AATSR.

Vegetation indices are estimated by taking theratio of radiance measured on several specificspectral channels.

In the image example, a model is used toderive the biomass from the NDVI(Normalised Differential Vegetation Indices).

The biomass image uses the following colour code:

– light yellow: zero biomass,– turquoise: 1-25 m3/ha,– brownish green: 51-100 m3/ha,– brownish red: 101-150 m3/ha,– bright red: 150 m3/ha,– black: water, mountains and clouds.

Forest Fires

Fire detection and mapping using remotesensing measurements have demonstrated that avaluable amount of information can be derivedin a systematic way by combining IR channelinformation with a time series of image data.

During the night, in the absence of reflectedsolar energy, the irradiance at 3.7 µm due to afire burning is much greater than thebackground Earth surface. Ready-to-use fireproducts (hot spot images and localisationfiles) from the ERS ATSR are already processedand made available to users through adedicated WWW server.

World land vegetation map derived from Vegetation Data(Image by courtesey of CNES)

NDVI estimation (left) and Biomass estimation (right) obtained from AVHRR (Images by courtesy of JRC (I))

Borneo forest fires imaged by the ATSR, October 1997(Image processed by ESA)

This service will be continued and fed with near real time products on theENVISAT mission.

34

Atmosphere

The GOMOS instrument has been designed toenable simultaneous monitoring of ozone andother trace gases, as well as aerosol andtemperature distributions in the stratosphere.Furthermore, it supports the analysis ofatmospheric turbulences. Trace gasconcentrations and other atmosphericparameters will be measured in the altituderange between 20 and 100 km with a verticalresolution of appr. 1.7 km.

The instrument accommodates a UV-visibleand a near-infrared spectrometer fed by atelescope which has its line of sight orientatedtowards the target star by means of a steerablemirror. The instrument then tracks the star andobserves its setting behind the atmosphere.Additional measurements provided by two fastphotometers allow correction of the spectraldata from the high frequency componentintroduced by atmospheric scintillations.

The 930 nm band of the near-infraredspectrometer permits derivation of verticalprofiles of water vapour, which is a majorcontributor in the ozone destruction process.From the 760 nm band of this spectrometer, thevertical temperature profile can be retrievedwhich provides data for the extraction of theozone concentration profile and for its longterm trend monitoring.

Earth

Line of SightStar Velocity Vector

TransmittedStellar Flux

OccultatedTransmittedStellar Flux

Polar Orbit

GOMOS

Pointing Direction

Atmosphere Layer

GOMOS Steering Front Mechanism

Global Ozone Monitoring by Occultation of Stars (GOMOS)


GOMOS will be operated continuously overthe full orbit. About 25 stars brighter thanMV = 2 can be observed routinely at differentlongitudes from each orbit. With 14.3 orbits/day,the GOMOS instrument will produce as muchdata as a global network of 360 groundstations. The instrument is typicallycommanded to observe a sequence of up to 50stars which are repeatedly observed onsequential orbits.

From the spectral analysis, spatial as well asshort, seasonal and long-term temporalinformation can be derived. As a result,detailed maps, profiles and trends for variousatmospheric constituents and parametersunder investigation can be obtained.

The excellent performance of the GOMOSinstrument stems from:

• the self-calibrating measuring scheme bydetecting a star’s spectrum outside andthrough the atmosphere,

• the drift and background compensatingmeasurement algorithms introduced by theuse of two-dimensional array detectors,which allow stellar and background spectrato be recorded simultaneously.


As a result, the spectra are easily corrected forbackground or stray light and detector darkcurrent contributions. Successive recordings ofstellar spectra outside and through theatmosphere allow any long-term changes inspectral emission characteristics, as well asdrifts in sensor spectral sensitivity, to becompensated.

From simple relative measurements highstability is thus obtained. Over a five yearmission period, ozone level changes as low as0.05 %/year can be detected, far below thedepletion rate expected from modelcalculations.

GOMOS is developed under leadership ofAstrium SAS (F).

Channel SpectralResolution

SpectralRange

250 - 675 nm

756 - 773 nm

926 - 952 nm

650 - 700 nm

470 - 520 nm

UV-VIS

IR 1

IR 2

PHOT 1

PHOT 2

20 km - 100 km

1.7 km

continuously over full orbit

222 kb/s

164 kg

187 W


1.2 nm

0.2 nm

0.2 nm

broadband

broadband

Optical PerformanceParameters

Altitude Range

Vertical Resolution

Operation

Data Rate

Mass

Power

Michelson Interferometer for PassiveAtmospheric Sounding (MIPAS)

MIPAS is a high-resolution Fourier TransformInfrared spectrometer which is designed tomeasure concentration profiles of variousatmospheric constituents on a global scale. It will observe atmospheric emissions from theEarth horizon (limb) in the mid infrared region(4.15 µm - 14.6 µm) providing globalobservations of photochemically interrelatedtrace gases in the middle atmosphere and theupper troposphere.

These data will contribute to the developmentof a better understanding in the followingresearch areas:

• Stratospheric Chemistry: global ozoneproblem, polar stratospheric chemistry,

• Global Climatology: global distribution ofclimate relevant constituents,

• Atmospheric Dynamics: stratospherictransport exchange between troposphereand stratosphere,

• Upper Tropospheric Chemistry: correlationof gas distribution with human activities.

The instrument is designed to allowsimultaneous measurement of more than 20relevant trace gases, including the completeNOy-family and several CFCs. Atmospherictemperature as well as the distribution ofaerosol particles, tropospheric cirrus cloudsand stratospheric ice clouds (including PolarStratospheric Clouds) are further importantparameters which can be derived from MIPASobservations.

GOMOS performance and budget data

IFOV3 x 30 km

RearwardViewing Range

SidewaysViewing Range

3010…2750 kmSub Satellite Track-

Tangential Height 5... 150km

Flight Direction

36

The data are obtained with complete globalcoverage, for all seasons and independent ofillumination conditions, allowing measurementof the diurnal variation of trace species.

Atmospheric emissions will be measured at thehorizon of the Earth (limb) over a height rangeof 5 km to 150 km. This observation geometryallows maximum measurement sensitivity anda good profiling capability to be achieved.

MIPAS will perform measurements in either oftwo pointing regimes: rearwards within a 35°wide viewing range in the anti-flight direction,and sideways within a 30° wide range on theanti-sun side. The rearward viewing range willbe used for most measurements, since itprovides good Earth coverage including thepolar regions. The sideways range is importantfor observations of special events, like volcaniceruptions, trace gas concentrations above majortraffic routes, or concentration gradients acrossthe dawn/dusk border.

MIPAS data products are calibrated high-resolution spectra which are derived on theground from the transmitted interferograms.From these spectra the geophysical parametersare retrieved, such as trace gas concentrations,temperature profiles, mixing ratios, and globalmaps of atmospheric constituents.

MIPAS is developed under leadership ofAstrium GmbH (D).

Instrument NESRo

Radiometric Accuracy

Spectral CoverageSpectral ResolutionSpectral Stability GoalElevation Scan RangeAzimuth Scan Range

Line of Sight Stability

Detectors Oper. Temperature



between 50 nW cm sr /cm at 685 cm-

and 4.2 nW cm-2sr -1/cm-1 at 2410 cm

2 . NESRo + 2% to 5% of source radiancedepending on wavelength

685 cm to 2410 cm-1

< 0.035 cm-1

-1

-1 -1

-1

-2

< 0.001 cm over 1 day-1

between 5 km to 150 km tangential height80° - 110° (sideways) and 160° - 195° - w.r.t. flight direction

Line of Sight Pointing Knowledge < 1.8 km in tangential height< 500 m/4 s in tangential height

65 K - 75 K

continuously over full orbit533 kb/s; Raw Data Mode 8 Mb/s327 kg196 W

MIPAS Interferometer (EM)

MIPAS performance and budget data


Channel SpectralResolution

SpectralRange

1

2

3

4

5

6

7

8


0.24 nm

0.26 nm

0.44 nm

0.48 nm

0.54 nm

1.48 nm

0.22 nm

0.26 nm

High ResolutionChannels

PolarisationMeasurementDevices (broadband)

Altitude Range

Vertical Resolution

Operation

Data Rate

Mass

Power

240 - 314 nm

309 - 405 nm

394 - 620 nm

604 - 805 nm

785 - 1050 nm

1000 - 1750 nm

1940 - 2040 nm

2265 - 2380 nm

310 - 2380 nmPMD 1 to 7 67 to 137 nm(channel

dependent)

10 km - 100 km depending on measurement mode

2.4 km - 3 km depending on measurement mode

continuously over full orbit

400 kb/s; 1867 kb/s real time mode

201 kg

119 W


Scanning Imaging AbsorptionSpectrometer for AtmosphericCartography (SCIAMACHY)

The primary scientific objective ofSCIAMACHY is the global measurement ofvarious trace gases in the troposphere andstratosphere, which are retrieved from theinstrument by observation of transmitted backscattered and reflected radiation from theatmosphere in the wavelength range between240 nm and 2400 nm. The large wavelengthrange is also ideally suited for thedetermination of aerosols and clouds. The nadir and limb viewing strategy ofSCIAMACHY yields total column values aswell as profiles for trace gases and aerosols inthe stratosphere. This enables, in addition,estimates of global trace gas and aerosolcontent and distribution in the lowerstratosphere and troposphere.

The measurements obtained fromSCIAMACHY will enable the investigation of awide range of phenomena which influenceatmospheric chemistry, i.e.:

• in the troposphere: biomass burning,pollution, arctic haze, dust storms andindustrial plumes,

• in the stratosphere: ozone chemistry,volcanic events and solar proton events.

In order to achieve the scientific objectives,measurements are performed by observing theatmosphere under different viewing angles. In Nadir Mode, the global distribution (totalcolumn values) of atmospheric trace gases andaerosols will be observed. Additionally, cloudmeasurements are obtained. In this mode, theinstrument is scanning across-track, with aswath width of ± 500 km with respect to thesubsatellite track. To obtain the altitudedistribution of trace gases, SCIAMACHYperforms observations in limb over an altituderange of 100 km, with a vertical resolution of3 km. Starting at Earth horizon, the atmosphereis scanned tangentially over a 1000 km wideswath. After each azimuth scan, the elevation isincreased until the maximum altitude of100 km is reached.

Differential Optical Absorption Spectroscopy isapplied in sun and moon occultationmeasurements, where either sun or moon aretracked or a vertical scan over the completesun/moon surface is performed. The obtainedspectra can then be compared with suitablecalibration spectra to yield the differentialabsorption of the atmosphere.

Sub SatelliteTrack

Nad

ir 8

00 k

m

1000 km

16 km x 32 km

TangentialHeight

100

km 0 km

1000 km x 1.3 kmLimb

-

Flight Direction

SCIAMACHY performance and budget data

Thermosphere

Mesosphere

Stratosphere

Stratosphere

Troposphere

O H O NO CO BrO p,T Aerosol100

90

80

70

60

50

40

30

20

10

0

GOMOS MIPAS SCIAMACHY

Ozone layer

3 2 N O2 CH42 NO3 HNO3 CO2

Alt

itu

de

[km

]

38

SCIAMACHY is developed by aGerman/Dutch/Belgian programme underDLR, NIVR and OSTC contract with AstriumGmbH (D) and Fokker Space (NL) as theleading companies.

The figure below shows the altitude rangesover which GOMOS, MIPAS andSCIAMACHY will measure the differentatmospheric constituents. The complementaryobservation among the three instruments – interms of altitude coverage, trace gas retrieved,spectral and spatial resolution – is what gives aunique potential to the ENVISAT atmospheric payload.

SCIAMACHY Flight Model

Primary atmospheric species observed by GOMOS, MIPAS and SCIAMACHY



Ozone and UV Radiation

Many of the factors affecting the globalenvironment are related to changes in thechemical composition of the atmosphere.

ENVISAT will make available globalmeasurements of the many chemical speciesaffecting the climate and will greatly contributeto improving forecasts of the Earth’s climate.

It will, in particular, improve our presentcapabilities to retrieve the global distribution ofozone in the atmosphere. Among many otherapplications, the ozone products, provided byENVISAT, will be assimilated into global ozonemodels. These models are used as the basis forreliable ultraviolet (UV) sunlight forecastsmade available to the public, since it is animportant hazard to be monitored for human health protection.

Ozone Depletion

The reduction in stratospheric ozoneconcentrations since 1960 is the direct result ofthe use of ozone depleting chemicals.Conversely, pollution at the Earth’s surface hasled to increased levels of tropospheric ozone,particularly over industrial areas, withconsequent threats to human health.

The figure alongside shows the time sequenceof the global distribution of total column ozonein the Southern Hemisphere, measured by theGOME instrument on board the ERS-2 satellite. The sequence starts in mid-July 1996 (upperleft) and ends in mid-March 1997 (lower right).Ozone depletion peaks in October, reachingrecord low values around 100 Dobson units.About 20 years ago the total column ozone wasabout 300 DU in this region. (The overheadvertical column of ozone is expressed in termsof the thickness of a sample of pure ozone atstandard temperature and standard pressure:l DU = 0.01 mm)

Clear-sky UV index12 Oct 2000 noon

KNMI/ESA

0 1 2 3 4 5 6 7 8 9 10 11 12 13 >14

Global UV Index forecasting for 15 November 2000, derived from GOME data(Image by courtesy of KNMI)

Southern Hemisphere ozone hole time sequence

15 July 1996

15 October 1996 15 November 1996 15 December 1996

15 March 199716 February 199715 January 1997

Dobson Units100 450

15 August 1996 15 September 1996

40

Aerosol Map

Global aerosol maps, generated by satellitemeasurements, give information about theradiative equilibrium of the Earth's atmospheresystem. Increased levels of stratosphericaerosols can reduce the amount of sunlightentering the Earth's atmosphere. Large volcanic

eruptions (e.g. Pinatubo during June 1991) mayeven globally affect power/fuel consumptionand agriculture.

The attached aerosol map shows high aerosolextinction values, in January 1992, followingthe Pinatubo eruption.

Aerosol map (optical extinction coefficient colour scale) based on SAGE II data, January 1992 after Pinatubo eruption (image by courtesy of BISA)


Greenhouse Effect

The greenhouse effect relates to the warming ofthe troposphere by increasing concentrations ofthe so-called greenhouse gases (carbon dioxide,methane, nitrous oxide, ozone and others). The warming occurs because the greenhousegases are transparent to incoming solarradiation, but absorb infrared radiation fromthe Earth that would otherwise escape from theatmosphere into space. The greenhouse gasesthen re-radiate some of this heat back towardsthe surface of the Earth. The rise in carbondioxide as a result of industrialisation isprimarily responsible for the enhancedgreenhouse gas effect. Current carbon dioxidelevels are more than double pre-industriallevels, and are the focus of international effortsto reduce emissions and offset theconsequences of changed climate patterns, sealevel rise, effects on hydrology, threats toecosystems and land degradation.

Vertical column of NO2 over Indonesia captured by GOME,indicating biomass burning events causing the NO2 generation


Trace Gases and Pollution

Lightning converts a tiny amount of inertnitrogen gas, which makes up 78% of air, intosoluble compounds that plants can take up intheir roots and metabolise. But the combustionof fossil fuels has unleashed a torrent of suchnitrogen compounds into the atmosphere.When oil, gas and coal burn at hightemperatures in engines and electric-powergenerators, they produce nitrogen oxides. Rain and wind carry these soluble compoundsto the earth, further enriching coastal watersalready replete with sewage and agriculturalrunoff. In all, fossil-fuel combustion accountsfor about 15% of the biologically availablenitrogen that human activities add to the worldevery year.

The rising concentration of methane (CH4) inthe atmosphere since the beginning of the 19thcentury is mainly due to changing agriculturalpractice, waste disposal, deforestation andmining. About 80% of the gas is produced bydecomposition in rice paddies, swamps, theintestines of grazing animals and by tropicaltermites. The levels of methane have risen by11% since 1978. The oxidation processes, whichremove methane from the atmosphere, can beimpaired by other emissions, principally thoseof man-made carbon monoxide, but also bynatural hydrocarbons from plants. Up to 40%of the rise in methane concentration is ascribedto this reduction in the natural rate of itschemical decay.

Also the CFC content of the atmosphere willremain a matter of concern for humanity forthe next 50 years, the time it is estimated forthese chemicals to disappear from the upperreaches of the atmosphere. The chemistry ofthe stratosphere is very complex, and theglobal measurement of these species or relatedreactive fragments leads to a betterunderstanding of atmospheric physics and chemistry.

Bromine species play a significant role in theprocess that control’s the amount of ozone inthe lower atmosphere. Since the launch ofGOME in 1995 the global monitoring ofbromine monoxide has become possible, andthese observations will be enhanced by thecoming ENVISAT atmospheric observations.

In addition, to CH4 and BrO, atmosphericconstituents such as SO2, NO2, NO3, N2O, andHNO3 are among the many other trace gasesthat MIPAS, GOMOS and SCIAMACHYwill measure.

Global GOME bromine monoxide map over the South Pole forOctober 1999, showing tropospheric BrO plumes (Image by courtesy BISA)

Global NO2 map measured by GOME

42

Altimetry


The new features of RA-2 enable it to extend toland the measurements of altitude andreflectivity.

The measurements will be used for thedetermination of Earth surface elevation,geological structure and surface characteristics.

RA-2 transmits radio frequency pulses whichpropagate at approximately the speed of light.The time elapsed from the transmission of apulse to the reception of its echo reflected fromthe Earth’s surface is proportional to thesatellite’s altitude. The magnitude and shape ofthe echoes contain information on thecharacteristics of the surface which caused the reflection.

On board the satellite, RA-2 measures withrespect to transmission, power level and timeposition of the samples of the earliest part ofthe echoes from ocean, ice and land surfaces.This result is achieved by one of the newfeatures on RA-2: a model-free tracker in theon-board signal processor that keeps the radarechoes within the sampling window. Windowposition and resolution are controlled byalgorithms developed to suit the trackingconditions. Adaptive height resolutionoperation is implemented by selecting thebandwidth of the transmitted pulses.

Radar Altimeter 2 (RA-2)

The Radar Altimeter 2 is derived from the ERS-1 & 2 Radar Altimeters, providingimproved measurement performance and new capabilities.

The main objectives of the RA-2 are the high-precision measurements of the time delay,the power and the shape of the reflected radarpulses for the determination of the satelliteheight and Earth surface characteristics.

Operating over oceans, these measurements areused to determine the ocean topography, thussupporting the research of ocean circulation,sea floor and marine geoid characteristics.

The processing of the radar echo power andshape on ground enables the determination ofwind speed and significant wave height in theobserved sea area, thus supporting, inaddition, the weather and sea stateforecasting.

Furthermore, the RA-2 is ableto map and monitor sea iceand polar ice sheets.

RA-2 Antenna (Photograph by courtesy of Alenia Spazio (I))


As a result, measurements over ocean arecarried out with improved accuracy at thehighest resolution. Over land, ice or duringtransitions from one kind of surface to another,the tracking is maintained, acceptingsometimes a certain degradation of the heightresolution. Accurate altitude measurementsover the ocean carried out by RA-2 at the mainfrequency of 13.575 GHz are affected byfluctuations in ionospheric characteristics.Measurements at a second frequency channelof 3.2 GHz enable the error to be corrected.

The RA-2 is developed under leadership ofAlenia Spazio (I).

Laser Retro-Reflector (LR)

The Laser Retro-Reflector is mounted on thenadir face of the satellite close to the RA-2antenna to support satellite ranging and RA-2altitude measurement calibration. The LR is apassive device which will be used as a reflectorby groundbased laser-ranging stations usinghigh power pulsed lasers.

The operating principle is to measure onground the time of a round trip of laser pulsesreflected from an array of corner-cubesmounted on the Earth-facing side of thesatellite. The corner-cubes are designed toreflect the incident laser beam back directly,making the reflected beam parallel to theincident beam within a few arcseconds.

The corner cubes are made of the highestquality fused silica optimised for maximumreflectivity at 532 nm and 694 nm. They aresymmetrically mounted on a hemisphericalhousing with one nadir-looking corner-cube inthe centre, surrounded by an angled ring ofeight corner-cubes. This will allow laserranging in the field of view angles of 360° inazimuth and 60° elevation around the nadir.

The LR is developed under leadership ofAlcatel Space Industries (F).

RA-2 performance and budget data


AltitudeBackscatter Coefficient

WaveheightMeasurement Datation

Operating Frequency

Bandwidth

Pulse Repetition Frequency

Pulse WidthIF Bandwidth


764 km to 825 km--10 dB to +50 dB

0.5 m to 20 m+/- 100 µs wrt. UTC

13.575 GHz (Ku-Band)3.2 GHz (S-Band)320 & 80 & 20 MHz & CW (Ku-Band)160 MHz (S-Band)1795.33 Hz (for Ku-Band)448.83 Hz (for S-Band)

interleaved operation20 µs6.4 MHz

continuously over full orbit68 kb/s nom.; 91 kb/s individual echoes111 kg130 W

Range Accuracy

< 4.5 cm (highest res.)< 0.4 dB (bias)< 0.2 dB (residual)< 5 % or 0.25 m

Laser Retro-Reflector FM (Image by courtesy of Alcatel SI (F))

44

Microwave Radiometer (MWR)

The main objective of the MicrowaveRadiometer is the measurement ofatmospheric humidity assupplementary information fortropospheric path correction of theRadar Altimeter signal, which isinfluenced both by the integratedatmospheric water vapour contentand by liquid water. In addition,MWR measurement data are usefulfor the determination of surfaceemissivity and soil moisture overland, for the surface energy budget,investigations to supportatmospheric studies and for icecharacterisation.

The MWR instrument is a derivative of theradiometers used on the ERS-1 & 2 satellites. It is a dual channel, nadir-pointing Dicke typeradiometer, operating at frequencies of23.8 GHz and 36.5 GHz. Differentialmeasurements at two frequencies have to beperformed in order to eliminate Earth’sirradiation.

With one feed horn for each frequency theMWR points via an offset reflector at an angleclose to nadir. The instrument configuration ischosen such that the 23.8 GHz channel ispointing in the forward direction, the 36.5 GHzchannel in the backward direction, with afootprint of about 20 km diameter for each beam.

In nominal Dicke operation, the measuredantenna temperatures are continuouslycompared with an internal reference load at aknown temperature. The measurement rangethus covered is 3 K to 335 K, with a referencetemperature accuracy of better than 100 mKand an absolute radiometric accuracy of betterthan 3 K over the full measurement range.

The MWR is developed under leadership ofAlenia Spazio (I).

Nadir

20 km 25 km

35 km

Sub Satellite Track

Flight Direction

-

Operating Frequencies

Dynamic RangeAbsolute Radiometric Accuracy



23.8 GHz (K-Band)36.5 GHz (Ka-Band)

3 K ... 335 K

1 K at T 300 K, better 3 K at T 85 K … 330 KANT ANT

Continuously over full orbit427 bit/s24 kg10 W

DORIS FM with MWR in the background (Photograph by courtesy of Sextant (F))

MWR performance and budget data



Doppler Orbitography andRadiopositioning Integrated bySatellite (DORIS)

DORIS is an orbit determination system,providing data of the satellite orbit with anaccuracy in the order of centimetres. In conjunction with the Radar Altimeter,DORIS contributes to climatology bymeasuring spatial and temporal ocean surfacetopography changes and variations in icecoverage. In addition, data are provided to:

• help in the understanding of the dynamicsof the solid Earth,

• monitor glaciers, landslides and volcanoes,

• improve the modelling of the Earth’sgravity field and of the ionosphere.

DORIS is based upon the accuratemeasurement of the Doppler shift of radiofrequency signals transmitted from groundbeacons and received on board the satellite.Measurements are made at two frequencies:2.03625 GHz for precise Dopplermeasurements, and at 401.25 MHz forionospheric correction of the propagation delay.

DORIS will allow determination of the satelliteposition with an accuracy of better than 0.05 mradial, and its velocity with an accuracy ofbetter than 0.4 mm/s.

The DORIS system comprises the on-boardinstrument, a beacon network and the DORISControl and Data Processing Centre. The DORIS Control Centre performsinstrument and beacon control on the basis ofmonitoring and telemetry data, and theoperational orbit determination.

DORIS is provided to the ENVISATprogramme by CNES (F).

DORIS Network, ENVISAT elevation: 12 deg, altitude: 800 km

Measurement Frequencyfor Doppler Measurementfor lonospheric Correction

Position AccuracyReal-TimeRestituted

Velocity AccuracyReal-TimeRestituted



2.03625 GHz401.25 MHz

< 1 m0.05 m radial

< 2.5 mm/s 0.4 mm/s

continuously over full orbit16.7 kb/s85 kg (incl. ICU)51 W (incl. ICU)

DORIS performance and budget data

46

Root mean square of sea level anomaly (in cm) obtained from merged ERS and T/P datafrom October 1992 to October 1997. Note the high resolution of the map brought by the

denser ground track mesh of ERS. (Courtesy of PY LeTraon, CLS, F)

Relation between sea floor and sea surface elevation

Wave and WindThe Radar Altimeter is able to measureroutinely wave heights (from the shape of theradar return echo) and wind speed at the oceansurface (from the strength of the returnedpower). Its measurements (together with thoseprovided by the Wave Mode of the SyntheticAperture radar) are commonly assimilated bythe meteorological forecasting centres aroundthe world.

This allows improvements of the wind and wavemodels which contributes to safer off-shoreactivities and more accurate routing of ships.

Ocean Topography and Ocean Circulation

Earth observation satellites, such as ERS-1 & 2,have revolutionised the study of the ocean.They now provide accurate repetitivemeasurements over remote areas of the world,where previously there were only sparseobservations from ships and buoys.

The ocean surface is not flat. The ocean surfacecarries signature of the shape of the sea floor, abumpy surface called geoid. A betterknowledge of the geoid carries informationabout the Earth's history.

The Radar Altimeter is able to measure oceantopography to a formidable degree of accuracy,in the order of centimetres.

Ocean circulation is generated by the combinedeffect of the attraction of the Moon and theSun, by the heating of the water by the Sun, bythe Earth's rotation, and by the winds. The water circulation carries heat from theEquator and the mid-latitudes towards thepolar regions. This giant heat transport processhas a powerful influence on the Earth's climate.

Typical ocean currents translate into oceansurface elevations of several tens of centimetres,easily observable by the Radar Altimeter.Variation of a few centimetres over a width ofseveral hundreds of kilometres correspond towater flow variations of several millions ofcubic meters per second, and therefore hugechanges in the ocean current heat transport. Toquantify the variations of the heat transport,these tiny variations of the surface elevationneed to be observed with the centimetreaccuracy achieved by the Radar Altimeter.

Wave heights as measured by ERS-2 Radar Altimeter in the summer of 1995(Processed by ESA 1996)



Ice TopographyTopography of large ice sheets is measured bythe Radar Altimeter, as illustrated by this mapof Greenland derived from the ERS RadarAltimeter.

The ESA altimetry missions (ERS-1 & 2 andnow ENVISAT), contrary to most altimetrymissions, have the unique capability, thanks tothe polar orbit, to map Antarctica, where mostof the world ice is stored. This is of paramountimportance in establishing if the ocean level isrising or not.

The Radar Altimeter on board ENVISAT (RA-2) has a specially designed tracking mode,with automatic adjustment of its trackingbandwidth to the underlying surface,maximising its capability to measure the iceshelf topography.

El NiñoThe El Niño phenomenon occurs when thenominal equilibrium is broken by theweakening of the trade winds. During an ElNiño event, the trade winds weaken, there isan eastwards flow of warm surface water, a rise of the sea level by up to 30 cm on theeastern side, and an interruption in the up-welling of nutrient rich waters. Fish die ormigrate to higher latitudes, and rainfallpatterns change dramatically, causing heavyrain and floods on the western coast of SouthAmerica and drought in Australia and south-east Asia.

During the last El Niño event, the RadarAltimeter and the ATSR, on board ERS-2,demonstrated very well their complementarycapabilities to measure and track the evolutionof the phenomenon.

The Radar Altimeter is able to measure the riseof the ocean surface due to the anomalouswarming of the water, monitoring thedevelopment and evolution of the El Niñophenomenon. The time series from March 1997to February 2000 illustrates the changes in theocean surface elevation as seen from the RadarAltimeter. The second figure illustrates thecombined use of measurements from the RadarAltimeter and ATSR instruments on board ERS.The Radar Altimeter measurements are shownas an increase of the ocean surface elevation,while the ATSR sea surface temperaturemeasurements are shown in colour code. The high correlation between the twomeasurements is clearly visible.

El Niño and La Nina 1997-2000 events as seen by altimetry

Antartica Ice balance velocitiesestimated from ERS Altimeter (Courtesy of F. Remy, LEGOS, F)

Combined sea surface elevation and sea surface temperature anomalies provided by theERS RA and ATSR during the El Niño event (image processed by ESA)

MARCH 97

DECEMBER 98 JULY 99 FEBRUARY 00

DECEMBER 97 MARCH 98

0 100 200 300in m/y

Filchner-RonneIce Shelf

RossIce Shelf

Byrd Glacier

Slessor Glacier

Lambert GlacierSystem

UK-PAC

F-PAC

DPAC

I-PAC

KIRUNAPDHS, LRAC,S-PAC

SVALBARD

ESRINPDCC, PDHS

E-PAC

ARTEMIS receive antenna at ESRIN

Kiruna Salmijärvi Station

48

G r o u n d S e g m e n t 49

Ground Segment

The Ground Segment provides the means andresources to efficiently manage and control themission, satellite operation and the provisionof services to the users.

The Ground Segment includes two majorelements:

• the Flight Operation Segment (FOS),

• the Payload Data Segment (PDS).

Flight Operation Segment (FOS)

With its Flight Operations Control Centre(FOCC), located at ESOC Darmstadt(Germany), and its two command and controlstations of Kiruna-Salmijärvi and Svalbard, theFOS provides control of the satellite through allmission phases.

The Kiruna-Salmijärvi station is the primarycontrol station for 9 to 10 consecutive orbits perday, the remaining 4 to 5 orbits per day areaccessed via the Svalbard station. For theLEOP, 7 extra stations will complete the stationnetwork to obtain good coverage of the critical events.

The FOCC prepares the satellite operationplans based upon a fixed strategy defined forthe Global Mission, and operation requestsreceived from the PDCC for the RegionalMission, composed of ASAR High Rate andMERIS Full Resolution. It also plans theARTEMIS related operations and interfaceswith the ARTEMIS mission planning facilities.

PDCC ( Payload Data Control Centre) at ESRIN (I)

NRT Services (Global & Regional level 1b and 2 products) - Two PDHS (Payload Data Handling Station) at Kiruna-Salmijärvi (S) and at ESRIN (I) - Two PDAS (Payload Data Acquisition Station) at Fucino (I) and Svalbard (N)

Offline Services (Global & Regional level 1b and 2 products)- LRAC Low Rate Archiving Centre for all level 1b global mission products at Kiruna-Salmijärvi (S)- D-PAC for all atmospheric products (with FMI for GOMOS) and ASAR* at DLR Oberpfaffenhofen (D)- F-PAC for RA-2, MWR and Doris Orbit products at CNES Toulouse (F)- I-PAC for ASAR and MERIS FR products* at ASI Matera (I)- E-PAC for MERIS FR products* at Maspalomas (E)- S-PAC for MERIS RR products, co-located with the LRAC at Kiruna-Salmijärvi (S) - UK-PAC for AATSR and ASAR * at NRSC Farnborough (UK)

Note: *For ASAR and MERIS FR, archive and offline services are shared between several PACs

The PDS centres and stations

The Flight Operation Control facilities arebased on an upgrade of the well-proven SCOS-1B system used for the two ERS missions. This upgrade has been performed withsuccessive deliveries allowing a stepwiseacceptance and validation process. A satellitesimulator, emulating the satellite on-boardsoftware, supports the operational proceduresvalidation and the FOCC operators’ training.

The Flight Dynamics software, derived fromthe ORATOS system already in use for ERS,was upgraded to support star tracker controland monitoring. The orbit prediction, orbitrestitution activities and orbit control/manoeuvre planning will be performed as forERS, with the same software and in-orbitcontrol strategy.

Payload Data Segment (PDS)

The PDS, coordinated by the Payload DataControl Centre (PDCC) located at ESRIN (I),comprises all those elements which are relatedto payload data acquisition, processing andarchiving, as well as those concerning userinterfaces and services. The PDCC builds upsatellite observation scheduling based uponuser requests, and provides it to the FOCC forsatellite operation planning.

With its four stations, the PDS acquiresdirectly, or in deferred mode via on-boardrecorder data dump, all payload data. They areprocessed in Near Real Time (NRT), providingto the users a complete suite of productswithin three hours from observation. For thispurpose, all operation strategies, with orwithout ARTEMIS, ensure that the data storedon board are dumped every orbit in visibilityof one of the ESA PDS stations.

50

G r o u n d S e g m e n t

For providing off-line products, the PDS relieson the Processing & Archiving Centres (PACs),implemented by national funding byparticipating states.

The ESA PDS centres and stations are providedvia a single ENVISAT PDS procurement, ledby Alcatel. The ESA PDS design is based upona modular architecture with building blocks(facilities). The various stations and centres arebuilt by assembly of these facilities.

Since the PACs are providing offline ESAproducts based upon the same processingalgorithms as the NRT products, the PACs arerequested to use the facilities developed for thePDS. These facilities are made available tothem as Generic Elements: each PAC procuresits computer hardware set up, on which thegeneric elements are installed, to build up thespecific configuration required to fulfil itsassigned tasks. With this approach, the usersget, for each instrument, a single suite ofcoherent products in NRT and Offline. ESA iscommitted to guarantee, with the support ofExpert Support Laboratories (ESLs) andthroughout the mission lifetime, continuouscalibration and validation of the PDS products,as well as processing algorithm upgrades asrequired. Consequently, only one set ofprocessors will be maintained and upgraded,ensuring coherency of all the user PDS serviceswhile minimising the corresponding overallmaintenance cost.

PDS Products and ValidationActivities

ESA is committed to provide, with the PDS, acomplete suite of Level 1b products and acomprehensive set of Level 2 products.

Level 1b products are geolocated dataproducts providing engineering quantitiesdirectly derived from the instruments:radiance, reflectance, transmittance,polarisation, radar backscattering values, radarecho time delay. These products are presentedas images for ASAR, MERIS and AATSR. All Level 1b products will be calibrated duringthe in-orbit Commissioning Phase. Varioustechniques will be involved using on-boardcalibration devices and/or specific modes ofthe instruments to observe targets in the sky(sun, moon, stars) or on the Earth (natural

stable targets, like deserts or tropical forests, aswell as specially developed targets, liketransponders or radar corner reflectors).

Level 2 products provide geophysical variablesobtained by processing further the Level 1bproducts using validated geophysicalalgorithms. Level 2 products providequantitative values for atmospheric variables(temperature, pressure, atmosphericconstituents, aerosol and cloud parameters), aswell as marine variables (ocean surface windand waves, ocean and coastal zone waterconstituents, sea surface temperature), andland variables (vegetation indices,temperature, pressure and reflectances).

For each geophysical data product, specificvalidation is required. It will be performed bycorrelation of the obtained data products withdifferent in situ measurements using ground-based, airborne and balloon-borneinstruments. In addition, comparisons will beperformed with other satellite data as well asanalyses based on the use of data assimilationmodels (meteorology, climatology, etc.).

Before the end of the Commissioning Phase, allthe Level 1b products will be released ascalibrated products. Most of the Level 2products will be released with notification tothe user of the corresponding confidences anderror bars. For products obtained fromENVISAT instruments having an ERS heritage,the validation will be performed within 6 months. For novelties such as MERIS and thethree atmospheric instruments, it is recognisedthat the validation will not be completed 6 months after launch.

Launch of a stratrospheric balloon to perform atmosphericin situ measurements

G r o u n d S e g m e n t 51

User Service Screen

The Radar Altimeter Mediterranean Calibration Campaign

User Services

The user services, via Internet, offer:

• a unified user interface, searchmechanism and ordering interface, withoutthe need to know where the data arephysically stored since all stations andcentres are linked by a PDS internalnetwork, (ordering of products requiringspecific data acquisition will be routed tothe PDCC),

• on-line browsing, for all imaginginstruments and the possibility of obtainingdirect on-line delivery of small products,

• ordering on a subscription basis forsystematic delivery of selected producttype(s) in NRT or Offline.

Data Policy

The Data Policy defines two categories of use:

• Category 1 use: for research andapplications development,

• Category 2 use: for operational andcommercial use.

For Category 1 use, 700 proposals, including130 proposals to support product validation,have been selected in response to anAnnouncement of Opportunity issued by ESA

in 1998. Category 1 use will be served directlyby the ESA PDS.

For Category 2 use, two world widedistributors have been selected, viz., SARCOM,led by Spotimage, and EMMA, led byEurimage. Some niche distributors have alsoapplied for specific licences, in accordance withthe provisions laid down in the approvedENVISAT Data Policy. The PDS services anddata products are provided to the distributors.

Structure Model in Hydra at ESTEC

Flight Model being prepared for RFC test at ESTEC

52

Engineering Model being prepared for RFC test at Bristol

O v e r a l l D e v e l o p m e n t a n d V e r i f i c a t i o n 53

The ENVISAT programme has followed aconventional design and developmentapproach, with units, instruments and sub-assemblies being tested to Qualification andAcceptance levels prior to delivery and theirsubsequent participation in the overall systemlevel development activities.

The development approach used for theENVISAT programme included a number ofmeasures implemented to reduce development,risks and costs:

• the physical and functional autonomy ofthe Service and Payload Modules (SM andPLM) allowed them to be developedin parallel,

• the re-use of SPOT-4 equipment in theService Module meant a number of itselectrical units’ designs had already beenqualified. This allowed the development of the SM to be based on a Protoflightapproach,

Overall Development and Verification

CONFIGURATION MODEL– Mechanical Interface Checks– Handling Trials– AIV Assembly & Access Checks

RF MODEL– Receivers & Transmitters Compatibility– Antenna Coupling– Verification of Modelling Techniques

FULL SCALEMOCK-UP

MOCK-UP

ANTENNAS

EMINSTRUMENTS

EM PEB

PFM SMEM PLC

StMINSTRUMENTS

StM SM

StM PLC

StM PEB

FMINSTRUMENTSPFM SM

FM PLC FM PEB

LAUNCH

FLIGHT MODEL (FM)– Flight Model Acceptance– Thermal Math. Model Verification (PLM)– ESOC System Verification

STRUCTURE MODEL (StM)– Mechanical Qualification– Unit Test Level Verification– Structure Math. Model Verification– MGSE and Facility Interface Verification

ENGINEERING MODEL (EM)– Electrical Qualification– EMC/RF Compatibility– H/W and SW Compatibility– EGSE and External l/F Compatibility

System Models: Objectives and build standard

• the ENVISAT payload instruments have maximum functional autonomy from the Polar Platform (PPF). Their development,qualification and acceptance is performed on a stand alone basis against instrument level requirements. This allowed them to be integrated with the PPF relatively late in the schedule for satellite level mechanical,electrical and functional tests,

• satellite qualification and acceptance isachieved by using three basic major satellitemodules depicted in the figure: theStructural Model (StM), Engineering Model(EM) and the Flight Model (FM),

• also, during the early development phase,two additional models were used: theConfiguration Model used to studyaccommodation and access, and the RF Mock-up Model used in support of the overall satellite RF analyses including RFinterference.

54

O v e r a l l D e v e l o p m e n t a n d V e r i f i c a t i o n

Since the ENVISAT instruments range fromcompletely new instruments to rebuilds ofexisting instruments with minimum adaptationfor accommodation on PPF, they had to betreated, from a development and verificationpoint of view, quite individually.

For newly developed instruments, performancerepresentative Engineering Models (EM) havebeen developed to get confidence as early aspossible that the instruments can fulfil theirmission objectives. Instrument EMs were builtflight representative in form, fit and function,and equipped with commercial componentssuitable for thermal vacuum testing.Redundancies were not required for the EMinstrument units.

Design qualification has been performed to themaximum extent possible for the givenprogrammatic constraints on the EM. On selected equipment, Protoflight Modelapproaches were accepted.

Verification has been completely performed atinstrument level against ENVISAT instrumentrequirements prior to their delivery to the PPFprogramme, i.e., as a general rule no satellitelevel tests were needed for instrument designqualification purposes. However, the satellitelevel tests were used to prove that theenvironment under which the instrumentdesign was qualified was compatible with theactual PPF environment.

After the instruments had been integrated onthe satellite, they participated in thecorresponding system level tests as outlinedbelow.

The following instrument hardware modelswere delivered to the spacecraft AIVprogramme:

• RF Mock-ups,

• Structure Models,

• Engineering Models,

• Flight Models.

Instruments

Flight Model following final instrument integration

Instruments


The Structure Model

The Structure Model satellite comprised a fullyrepresentative structural model of the PPF,structural models for those instruments orassemblies with a first eigenfrequency below100 Hz, and mass dummies for others. The programme was successfully completed in1996, and achieved mechanical qualification ofthe structure, verification of mechanical groundsupport equipment and facility interfaces, andverification of handling procedures.

A dedicated follow-on programme ofqualification against ARIANE 5 separationshocks was successfully completed in early2000 by adopting a Protoflight approach on theFlight Model Service Module.

The achievements of the StM test programmewere:

• confirmation of SM & PLM Static LoadCapability,

• confirmation of SM StM Clamp-band andPLM StM Appendage Release shocks,

• establish SM StM Mass Properties,

• confirmation of PPF StM Mass Modalbehaviour,

• qualification of structure at ARIANE 5Acoustic noise and Vibration levels,

• confirmation of PPF StM Alignment,

• fit check of StM PLM in the Large SolarSimulation facility at ESTEC.

Satellite

Structure Model integration at Astrium Ltd., Bristol

56


The Engineering Model

The Engineering Model satellite comprised theProtoflight Service Module, assembled with theEngineering Model Payload Module integratedwith electrically representative models of theinstruments. The Engineering Model satelliteprogramme was successfully completed inApril 1999, and achieved all its objectives toverify the electrical design, to validateassembly, integration and test procedures, and aspects related to the satellite’s operation.

The achievements of the test programmeincluded:

• confirmation of the electrical interfacesbetween the SM and the PLM and thesuccessful integration of all the EMinstruments,

• confirmation of the satellite functionalityincluding Bit Error Rate and Datation tests,

• confirmation of EMC performance,

• confirmation of RFC performance,

• system Validation Tests with ESOC,

• instrument special performance tests forsome instruments,

• development of user test software,

• update software and test procedures inreadiness for the FM programme.

Engineering Model during integration at Bristol


The Flight Model

The Flight Model satellite comprises theProtoflight Service Module and the FlightModel Payload Module equipped with theENVISAT payload complement. The FlightModel PLM structure is assembled from therefurbished StM primary structure fitted withnew secondary structure panels.

Following completion of the EM PPFprogramme, the Service Module underwent aplanned retrofit activity, including upgradingof software and some units.

Following their own design and developmentprogrammes, the Payload Instrumentssuccessfully completed their individualqualification programmes, thus permitting thefinal build of the Flight Models.

Once the Flight Model Instruments and PEBhad successfully completed their verificationtest programmes, they were integrated onto the PLM.

The achievements of the Flight Modelprogramme include:

• integration of the Flight Model PayloadModule (Instruments and PEB),

• thermal Balance and Vacuum testing atPLM level (SM already completed),

• Protoflight qualification for shock,

• integration of the FM PLM to the SM,

• Acceptance level acoustic noise testing,

• end to end release tests of Solar Array, Ka-Band mast and ASAR antenna,

• Acceptance level vibration testing,

• completion of RFC/EMC verification(partially performed already during the EM programme),

• overall system performance testing,

• verification of interfaces with MissionControl Centre, and flight operationsprocedure check-out,

• verification of full functionality ofinstruments and complete satellite by anumber of overall system tests.

Flight Model in preparation for RFC test at ESTEC (instruments protected by covers)

58


For the Flight Operation Segment (FOS), thefollowing approach was followed:

• incremental delivery and integration of theFlight Operation Control Centre (FOCC),

• four System Validation Tests (SVTs) usingsatellite databases delivered according tothe SVT needs,

• production of the Flight OperationProcedures (FOPs) based upon the satellitecontractor deliveries of the Flight OperationManuals (FOMs) and the TM/TCdatabases,

• simulation campaigns at the FOCC, to trainoperators and to verify correctness andcompleteness of the procedures starting 6 months before launch.

For the Payload Data Segment (PDS), a similarincremental integration/validation approachwas followed:

• Factory Acceptance Testing of thefacilities, building blocks of the PDS, priorto their integration on the PDS referenceplatform located in Rome,

• incremental integration and acceptancetesting on the reference platform of thecomplete centre and station configurationsprior to deployment on their final sites,

• on-site deployment and acceptance of PDSversion V1, and later on V2 versions,including their operational communicationnetwork. The PDS V2 version was acceptedin March 2000.

Upgrading to PDS version V3 was initiated to provide:

• capability for the PDS to run on new andmore powerful computers, reducingthe procurement and operation cost of the PACs,

• implementation of updated instrumentprocessing algorithms.

The PDS V3 version was accepted in April2001. This version will support the in-orbitcommissioning.

The Ground Segment Overall Validation(GSOV) completes the pre-launch testingactivities. It comprises:

• all interfaces tested before launch inrealistic operation scenarios. This isparticularly relevant for the missionplanning interfaces between FOS and PDS,

• propagation of test scenarios within theFOS and PDS towards execution of thecorresponding operation plans for end toend validation and operation rehearsalswith the operators,

• verification of the external interfaces withthe Announcement of OpportunityInstrument Providers and the Institutessupporting the instrument calibration andvalidation activities,

• integration testing of the PACs with theESA PDS, leading to PAC acceptance by ESA.

Ground Segment


The last months before launch will be used atFOS and PDS to execute operation simulationcampaigns to validate the procedures and totrain the respective operators for the early in-orbit operations and the CommissioningPhase.

The Calibration and Validation participantshave already participated in rehearsal testcampaigns with access to the User ServiceFacilities and to the ENVISAT campaign database. Simulated ENVISAT PDS products (a setof 10 CDs) have already been widelydistributed to the user community. These CDsare available upon request to the ENVISATHelpdesk: [email protected].

Simulated PDS products on CD

The Ground Segment preparation activities areon schedule:

• to control the satellite throughout thelaunch and early in-orbit operations,

• to support the Commissioning Phaseactivities, leading to availability of calibrated Level 1b and validated Level 2products,

• to respond to user needs with timelydelivery of NRT and Offline ESAcalibrated/validated products.

Further information regarding the ENVISATmission, can be obtained from the ENVISATwebsite: http://envisat.esa.int

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The ENVISAT Earth Observation Satellite hascompleted its design and developmentprogramme, achieving the objectivesestablished at the time of its approval.Exhaustive testing over the last two years hasdemonstrated compliance with all satellitedesign and performance requirements for afive year multi-disciplinary polar orbitingmission. The Launch Campaign will lead toENVISAT in space by the late summer of 2001.


61O v e r a l l D e v e l o p m e n t a n d V e r i f i c a t i o n 61

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Acknowledgement

The ENVISAT programme is carried out onbehalf of the European Space Agency by aconsortium of over 120 companies fromEurope, Canada and Australia.

ESA and Astrium acknowledge the work of allparties involved in contributing to thesuccessful development of ENVISAT. The spiritof common interest on customer and industrysides is very much appreciated.

Design and Print

Harley – The Communications Agency Bristol UK

May 2001

Documents

Flight Model in ﬁnal preparation for RFC test at ESTEC