Products IGS

8/10/2019 Products IGS

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Jan Kouba

Geodetic Survey Div.

NRCan

Canada

IGS Products and Applications


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Content

IGS Combined Products

Objectives

Description

Precision/availability

Consistency

Use of IGS Products

Relative Positioning

Precise Point Positioning/Navigation

Compatibility

Scientific Applications

IGS Products Limitations and Solutions

Future Developments


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IGS PRODUCTS

Support practical positioning and scientific applications of GPS, such as

surveying, navigation and national geodetic control networks

monitoring of Earth rotation, deformation and atmosphere (trop. & ion.)

easy access and contributions to ITRF, time transfers, etc.

Provides convenient and precise IGS reference system through

the core IGS combined products: orbits, Earth rotation parameters (ERP), station

positions/velocities and satellite/station clocks

additional combined products, consistent with the core products: tropospheric

zenith path delays (ZPD), ionospheric TEC (total electron count) maps and

associated rec./satellite diff. calibration biases (DCB)

IGS combined orbits (since 1994) ; clocks and ERP (since 1995); station

positions (since 1996) and tropospheric ZPD (since 1997)

IGS Products are more precise and reliable than the individual AC solutions

(up to 8 Analysis Center solutions combined)


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IGS Product Description

Core Combined Products: orbits/clocks/ ERP/station positions

IGS Final orbit, clock and ERP combined solutions (12 day delay)

IGS Rapid orbit, clock and ERP combined solutions (17 hour delay)

IGS Predicted orbit and clock combined solutions (1 hour before the observation day) Nine Associate ACs (AACs) produce regional station position solutions in SINEX format

Up to eight ACs, AACs contribute global orbit, ERP, global station position (SINEX)

solutions and up to five ACs clock solutions

Combined Zenith Path Delay (ZPD)

seven ACs, produced by GFZ, since Jan. 1997

Weekly files by site, 2 hour resolution (four weeks delays)

Combined Global Ionosphere Maps of Total Electron Content (TEC)

Five ACs, AACs, Combined TEC and DCBs (Differential Code Biases) in IONEX format,

produced by ESA since June 1998

Daily files, 2 hour resolution (four weeks delay)


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Analysis Center Functions

IGS Analysis Centers (AC): are the basis of all IGS products, improved IGSproducts are largely due to AC improvements

Typically performs continuously (daily): three types of global solutions(Predicted, Rapid and Final) utilizing complex and sophisticated software, often

developed in house over many years

Conforming to IGS/IERS standards, but innovations are encouraged.

Documentation on an each AC

) approach is at the IGS CB Archives:

http://igscb.jpl.nasa.gov/igscb/center/analysis/

ccc

.acn

Continuously involved in research & developments: striving for the bestsolutions and sharing scientific results amongst AC colleagues

Helpful and healthy competitions amongst all ACs

Associate Analysis Centers (AACs):

typically do not perform all global solutions, e.g. the Rapid only, or only certainspecific solution products, such as:

RNAAC (Regional Network AAC), GNAAC (Global Network AAC), IAAC(Ionospheric AAC) etc.


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IGS PRODUCT Table

IGS Combined Product Precision

Product Available Interval Precision

Satellite Orbits&clocks orbits clocks

Predicted Real-time 15 min 50 cm 30 ns

Rapid 17 hours 15 min 10 cm .5 ns

Final 12 days 15 min 5 cm .3 ns

IGS Combined (Prelim.) Station Positions Velocities

Weekly solutions 2-4 weeks 7 days 3-5 mm 1-3mm/y

Earth Rotation Parameters parameters rates/LODRapid PM 17 hours 1 day .2 mas. .4 mas/d

Final PM 12 days 1 day .1 mas .2 mas/d

Rapid UT /LOD 17 hours 1 day .10 ms .06 ms/d

Final UT /LOD 10 days 1 day .05 ms .03 ms/d

Tropospheric ZPD


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IGS Orbit Improvement

1994 to Mid 1999


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IGS PRODUCTS (AC performance)

BROADCAST (BRD), IGS PREDICTED (IGP) and IGS UTRA_RAPID

(IGU) ORBIT RMS WITH RESPECT TO THE IGS RAPID (IGR)

ORBITS

0

1

2

3

4

5

6

7

16-Nov-99 16-Dec -99 15-Jan-00 14-Feb-00 15-Mar-00 14-Apr-00 14-May-00

DATE

WEIGHTEDRMS(m)

brd

igp

igu


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IGS Orbit Comparison


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Earth Rotation Parameters


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Consistency of IGS Products

Consistent with the current international conventions

International Earth Rotation Service (IERS) Conventions 1996

International Terrestrial Frame (ITRF)(currently ITRF97)

IGS CORE products (orbits/clock/ERP/stations) are mutually consistent

Since December 1998, combination of minimally constrained AC solutions

Nearly exact ITRF transformations (e.g. for the ITRF97-ITRF96 and the future

changes)

ITRF realizations used for IGS Products (for more details see the presentationon: IGS ITRF Realization and Transformations) :

ITRF92 - Jan 2, 1994(Wk 0730) to Dec 31, 1994 (Wk 0781) ITRF93 - Jan 1, 1995(Wk 0782) to Jun 29, 1996 (Wk 0859)

ITRF94 - Jun 30, 1996(Wk 0860) to Feb 28, 1998 (Wk 0946)

ITRF96 - Mar 1, 1998(Wk 0947) to July 31, 1999 (Wk1020)

ITRF97 - Aug 1, 1999(Wk 1021) to present (since Feb 27, 2000 IGSITRF97 (SINEX))

IGS satellite clock solutions are aligned to the GPS time via broadcast clockcorrections:


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USE of IGS PRODUCTS

IGS Products greatly enhance and simplify (no need for complex global

GPS solutions) all GPS analyses and applications such as:

Positioning/navigation

Global, Regional and Local

Relative positioning with respect to the IGS station Polyhedron of about 200 stations atthe mm/ppb level (IGS orbits/ERP and station positions can be fixed even for

baselines 2000 km and longer). No need for precise satellite clocks (nearly

eliminated)

Absolute, precise point positioning ppp) worldwide, with respect to the IGSReference Frame IGS orbit/clocks/ERP held fixed) at mm precision level

Absolute, precise point navigation worldwide (ground, air, LEO satellites - no basestations needed ), at a cm precision level

Global Change Monitoring: solid Earth, atmosphere and oceans

ERP monitoring

plate motion and crustal deformation monitoring, volcanoes, etc.

monitoring of atmosphere (troposphere and ionosphere)

Precise time and freq. transfers (future contributions to UTC)


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Relative position precision at ppb/mm

IGS Orbits, ERP, base station position solutions can be held fixed at the IGS

solutions for all, even extreme, baseline lengths at ppb/mm precision level (in

ITRF insensitive to ERP)

When using double differencing, potentially more robust (than precise point

positioning), the IGS products ease data cleaning, ambiguity fixing

Complete covariance/correlation matrix available (e.g. for in SINEX format)

Suitable for continental, regional, national ITRF densification (e.g. EUREF -

normal equation matrix stacking of RNAAC SINEX solutions)

Warning: fixing IGS orbits/ERP implies very precise reference orientation and scale

even for (SINEX) unconstrained solutions (I.e. no stations fixed)

For long baselines (~ 1000km) ITRF orientation/scale changes need to be taken into

account prior normal matrix stacking

Insensitive to incompatibilities and clock errors

Insensitive to clock errors and all small (cm) ITRF changes for baselines


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Relative Positioning Rrequirements for cm Precision ( double differenced phase data with, or without phase

ambiguity fixing ; ~ 1 h occupancy)

IGS Products/ Baseline < 10 km 10 100 km 100 1000 km >1000 km

IGS Orbits No (Broadcast) IGS Rapid IGS Rapid/Final IGS Final

IGS ERP**** No No No NoIGS Sat Clocks No No No IGS Rapid/Final

IGS Iono Delays IGS iono* IGS iono* No** No**

IGS Tropo Delays Nominal/IGS tropo IGS tropo/ estimate Estimate Estimate

IGS ITRF Trasform No No No Yes

ERROR MODELS

IGS Ant phase center No Yes*** Yes*** Yes

Solid Earth tides No No Yes Yes

Ocean loading No No Yes YesRelativity correction No No Yes Yes

Sat phase wind up No No No Yes

Single frequency data; ** Two frequency data; *** For different antenna types only;

**** IGS ERP implied by IGS Orbits


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Precise Point Positioning

IGS combined Orbits, clocks held fixed in single point solutions

Equivalent to back substitution into complex, global (IGS) solutions

An efficient, flexible and convenient interface/access to the IGS reference frame

mm precision level for static point positioning worldwide, no base (IGSPolyhedron) station positions/data required

cm precision level for (epoch by epoch, ground, air, LEO sarellite) navigation, no

base (DGPS) station positions/data required.

Efficient and precise solutions for station clocks and tropospheric ZPDs

Disadvantages (wrt to double differencing/relative positioning)

More difficult to clean/edit data and/or to fix integer phase ambiguities

Sensitive to clock errors and to incompatibilities (see below) and even small

reference (ITRF) changes; orbits/clocks/ERP must be consistent

Correlation/variance matrix (amongst stations) lost and not available, thus not

well suited for national/continental ITRF (SINEX) densification


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Precise Point Positioning

Static Point Positioning Requirements (undifferenced phase/pseudorange data; < 1 h occupancy)

IGS Products/precision < 1 cm 1 10 cm 10 100 cm >100 cm

IGS Orbits IGS Final IGS Rapid/Final IGS Rapid/UltraR No (Broadcast)

IGS ERP*** No No No No

IGS Sat Clocks IGS Final IGS Rapid/Final IGS Rapid/UltraR No (Broadcast)

IGS Iono Delays No** No** IGS iono* IGS iono*

IGS Tropo Delays Estimate Estimate/IGS tropo IGS tropo/estimate Standard/nominalIGS ITRF Trasform Yes No No No

ERROR MODELS

IGS Ant phase centre Yes Yes No No

Solid Earth tides Yes Yes Yes No

Ocean loading Yes Yes No No

Relativity corrections Yes Yes Yes Yes

Sat phase wind up Yes Yes No No

* Single frequency data; ** Two frequency data; *** IGS ERP implied by IGS Orbits

Note:in near future,the Ultra Rapid IGS orbits (Ultra R )


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Precise Point Positioning (PPP)


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Precise Navigation

Navigation/Kinematic Point Positioning Requirements (undifferenced phase and pseudorange data;

instantaneous occupancy)

IGS Products/ precision < 10 cm 1050 cm 50500 cm >500 cm

IGS Orbits IGS Final IGS Rapid/Final IGS Rapid/Final No (Broadcast)

IGS ERP *** No No No No

IGS Sat Clocks IGS Final IGS Rapid/Final IGS Rapid/Final No (Broadcast)

IGS Iono Delays No** No** IGS iono* IGS iono*

IGS Tropo Delays Estimate Estimate/IGS tropo IGS tropo/estimate Standard/nominal

IGS ITRF Trasform Yes No No No

ERROR MODELS

IGS Ant phase centre Yes No No NoSolid Earth tides Yes Yes No No

Ocean loading Yes No No No

Relativity corrections Yes Yes Yes No

Sat phase wind up Yes No No No

* Single frequency data; ** Two frequency data *** IGS ERP implied by IGS Orbits


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Compatibility

IGS CORE products (orbits/clock/ERP/stations)

Mutually compatible and consistent since Dec 1998

Consistency of orbits and clocks is of utmost importance for precise point positioning

IGS station (SINEX) solutions are compatible/consistent with IGS antenna offsets (station logfiles) and the antenna calibration (phase center) tables (IGS_01.pcv) at IGSCB Archives

IGS satellite clock solutions are based on/compatible with the following

assumptions/conventions:

Periodical special relativistic correction : - 2 . X .V/c2 applied

Cross correlation type of pseudoranges : C/A; P2= C/A + P2-P1)

: P1, P2 (After April 2, 2000, Wk 1056)

Adopted satellite antenna offsets (X,Y,Z m)

Block II/IIA : 0.279 0.000 1.023 (in the satellite fixed frame)

Block IIR : 0.000 0.000 0.000

no L1-L2 satellite/receiver calibration delayed applied

Ionospheric TEC grid maps, satellite/receiver calibration biases must be of the same solutions

and

corresponding mapping function and DCBs must be used for all ionospheric applications to derive

slant ionospheric delays)


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Compatibility

Solid Earth tides have once and twice daily periods; can reach up to 300 mm in height and

up to 50 mm in latitude and longitude.


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Compatibility

Ocean Loading Effects have once and twice daily periods; can reach up to 50 mm in height

and up to 10 mm in latitude and longitude.


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Earth Orientation Parameter (EOP) monitoring

IGS Polar Motion rates of unprecendeted precision (0.1 mas/day) and resolution

(1 day, or even 2 hours for CODE AC solutions )

Continuously available with delays of less than 24h (IGS Rapid)

Independent short period (


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Correlation between Polar Motion Rates (Xrt, Yrt (not shown)) and OAM+AAM is nearly always better

than 0.8 (except for the low signal period at or below 0.25 mas/d)


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Water Vapor Estimates Comparison

at Station Potsdam

Partial Water Vapor (PWV) from GPS at IGS station POTS (Germany) agrees with

Water Vapor Radiometer (WVR), well within one mm (Courtesy of GFZ).


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Limitations and Solutions

IGS Combined Orbits :

In 24 h files with 15 min sampling (0-23:45 GPS time); can be easilyconcatenated to span daily boundaries; easily be fitted with low order

polynomials for continuous representation

Small daily discontinuities (at the dm level)

Possible orbit origin offsets (biases at the cm level)

Improvements at the AC level, I.e. smaller daily AC orbit discontinuities

(


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Recent Changes and Improvements

IGS Preliminary SINEX Combined Products became official

From Feb 20/00 (GPS Week 1050), aligned to ITRF97 ( using min. constraints)

SeeIGS Mail 2740

for more details

New IGS ITRF97 realization (through the IGS SINEX combined solution

IGS00P04.snx

product)

From Feb 27/00 (GPS Week 1051); delay increased from 10 to 12 days

Improved ITRF97 realization for the IGS Final orbits/ERP/clocks

No noticeable changes to the IGS users (no transformation, no steps )

SeeIGS Mail 2750

and

2751

for more details

New Pseudorange bias convention

starts on Apr 02/00(wk 1056)

P1, P2replace the current convention: C/A, P2= C/A + (P2-P1)

Important forIGS clock users (precise point positioning, time transfers)

SeeIGS Mail 2744

for more details and the adopted C/A-P1 biases

IGS Ultra-Rapid Comb. Orbits/clocks

testing started Mar 2/00


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Future Developments

Improved IGS ITRF realization (see the next presentation)

Weekly, Preliminary SINEX combinations, official since Feb 20, 2000

Up to 250 IGS Polyhedron stations IGS Combined SINEX solutions

Continuous plate motion monitoring/quality check (under way)

Ultra Rapid products Pilot Project (


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QUESTIONS?

Jan Kouba

Geodetic Survey Division

Natural Resources Canada (NRCan)

615 Booth Street

Ottawa, Canada K1A OE9

[email protected]

Tim Springer (The IGS AC Coordinator)

Astronomical Institute, Univ. Bern

[email protected]

For details on IGS Products, see the IGS Annual Reports

http://igscb.jpl.nasa.gov/overview/pub.html

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