Global Greenhouse Gas Observation by Satellite

Global Greenhouse Gas Observation by Satellite

1 Greenhouse gases Observing SATellite Project

The Greenhouse Gases Observing Satellite (GOSAT)

will be the world’s fi rst satellite to observe the con-

centrations of carbon dioxide and methane, two major

greenhouse gases, from space. (Fig. 1)

Analyses of GOSAT observation data will make it pos-

sible to ascertain the global distributions of carbon di-

oxide (CO2) and methane (CH

4) and the geographical

distribution of and seasonal and inter-annual variations

in the fl ux (i.e., emission and absorption) of greenhouse

gases. The results of the analysis will not only contrib-

ute to a deeper scientifi c understanding of the behaviors

of the causative agents

of global warming, but

will also provide fun-

damental information

for refi ning climate

change prediction and

formulating global

warming countermea-

sures. The GOSAT

Project is a joint effort

of the Ministry of the

Environment (MOE),

the National Institute

for Environmental

Studies (NIES), and the Japan Aerospace Exploration

Agency (JAXA) (Fig. 2).

Greenhouse gasesObservingSATellite

Figure 1. Overview of GOSAT (©JAXA)

NIES: National Institute for Environmental StudiesDeveloping and improving

methods to derive green-

house gas concentrations

from satellite and auxiliary

data

Higher-level processing,

validation, and distribution of data products to exter-

nal parties

Estimating carbon fl ux using models

Cooperating with JAXA activities

MOE: Ministry of the EnvironmentDeveloping sensors (in collaboration with JAXA)

Validating processed products

Contributing to international efforts to reduce carbon

emissions through scientific application of GOSAT

observation data.

Figure 2. Role Sharing in the GOSAT Project

NIESNIES JAXAJAXA

MOEMOE

JAXA: Japan Aerospace Exploration Agency

Developing sensors (in collaboration with MOE)

Developing, launching and operating the satel-

lite

Acquiring satellite observation data, including

data reception and recording

Level 1 processing of data and its calibration

Cooperating with MOE and NIES activities

Shared ResponsibilitiesManaging the Science

Team and promoting

data utilization

2

Goals of the GOSAT Project

Emissions of CO2 have increased drastically

over the past century as a result of the mass consumption of

fossil fuels due to the expansion of industrial activities re-

sulting in dramatic increases in atmospheric concentrations

of CO2 (Fig. 3). CO

2, which is a greenhouse gas, leads to an

increase in atmospheric temperatures. In addition to CO2,

species such as CH4, nitrous oxide (N

2O), and halocarbons

were designated as greenhouse gases subject to restrictions

by the Kyoto Protocol; however, CO2 and CH

4 account for

81% of the total greenhouse effect caused by these gases

(Fig. 4). The growing concentration of greenhouse gases in

the atmosphere not only raises the temperature but can also

cause droughts where rainfall is already scarce and fl oods

in places where precipitation is already abundant, so there

are concerns that, without intervention, signifi cant damage

will occur.

That being the case, the global community is moving to-

ward reducing greenhouse gas emissions. Under the United

Nations Framework Convention on Climate Change, the

Kyoto Protocol, which defi nes targets for emission reduc-

tions by developed nations, was agreed upon in 1997 and

came into force in February 2002. In order for every nation

on the globe to adopt measures for reducing greenhouse gas

emissions, it is essential to set rational goals based on ac-

curate predictions of climate change and its impact. At the

same time, it is important to determine emission levels per

country, and to evaluate various reduction measures based

on that knowledge.

The foremost purpose of the GOSAT Project is to produce

more accurate estimates of the fl ux of greenhouse gases on

a subcontinental basis (several thousand kilometers square).

This is expected to help contribute to environmental admin-

istration efforts such as ascertaining the amount of CO2 ab-

sorbed or released per region and evaluating the carbon bal-

ance in forests. Furthermore, by engaging in research using

the GOSAT data, we will accumulate new scientifi c knowl-

edge on the global distribution of greenhouse gases and its

temporal variations, and the mechanism of the global carbon

cycle and its effect on climate, which will prove useful in

predicting future climate change and assessing its impact.

Additionally, the Project will expand upon existing earth-

observing satellite technologies, develop new methodologies

to measure greenhouse gases, and promote the technological

development necessary for future earth-observing satellites.

CO2

conc

entra

tion

(ppm

) N2O

conc

entra

tion

(ppb

)

400

350

300

250

Year0 500 1000 1500 2000

2000

1800

1600

1400

1200

1000

800

600

CH4

conc

entra

tion

(ppb

)Carbon dioxide (CO2)Methane (CH4)Nitrous oxide (N2O)

Figure 3. Changes in concentrations of primary greenhouse gases in the atmosphere (Modifi ed from the IPCC Fourth Assessment Report)

Halocarbons13%

Nitrous oxide (N2O) 6%

Methane(CH4)18%

Carbon dioxide (CO2)63%

Figure 4. Contributions of the primary greenhouse gases to the increase in air temperature

(The above figures are based on the best-estimates of radiative forcing gases from 1750 to 2005, modifi ed from the IPCC Fourth Assessment Report)

Figure 5. The data obtained through GOSAT is expected to allow for this kind of computation of the global dis-tribution of CO2 fl ux

(Simulation, (a) February, (b) August, carbon con-version [gC/m2/day])

(b) A

ug

us

t

(a) F

eb

ru

ary

← Absorption Emissions →

Goals of the GOSAT Project1


GOSAT Sensors and Observation Methods

GOSAT will observe infrared light reaching

its sensors from the earth’s surface and the atmosphere

and give spectra which can be used to calculate the col-

umn abundances of CO2 and CH

4. The column abun-

dances are expressed as the total number of molecules

of target gases over the unit surface area or as the ratio

of target gas molecules to the total number of molecules

in dry air per unit surface area.

GOSAT will orbit the earth in roughly 100 minutes at an

altitude of approximately 666 km and return to the same

orbit in three days (Fig. 6). The observation instrument on-

board the satellite is called the Thermal And Near-infrared

Sensor for carbon Observation (TANSO). TANSO is com-

posed of two sensors: a Fourier Transform Spectrometer

(FTS) and a Cloud Aerosol Imager (CAI). Tables 1 and 2

summarize the target species, bands, and other specifi ca-

tions of the two sensors.

TANSO-FTS utilizes optical interference, which is in-

duced by splitting the incoming light into two optical paths

to create an optical path difference between the two, and

then recombining them. A light intensity distribution as

a function of wavelength (spectrum) can be obtained by

conducting a mathematical conversion called the Fourier

transform on the signals observed while changing the opti-

cal path difference little by little.

Bands 1 to 3 of FTS will provide the spectra of sunlight

refl ected from the earth’s surface in the daytime and band

4 will observe light emitted from the atmosphere and the

earth’s surface throughout the day and night. The charac-

teristics of sunlight refl ection differ greatly between land

and water surfaces. Seawater and freshwater absorb light

which makes detection of the refl ection diffi cult. However,

in certain directions, sunlight is refl ected as specular re-

fl ection and glitters brightly, so the sensor will target such

points for observation over large water surfaces.

TANSO-CAI will observe the state of the atmosphere and

the ground surface during the daytime in image form. The

imagery data from TANSO-CAI will be used to determine

the existence of clouds over a wide area including the fi eld

of view of FTS. When aerosols or clouds are detected,

the characteristics of the clouds and the aerosol amounts

are identifi ed. This information is used to correct for the

effects of clouds and aerosols on the spectra obtained by

FTS.

Over a three-day period, TANSO-FTS will take spectra

from several tens of thousands points distributed uniform-

ly over the surface of the earth. Since analysis can only be

done on cloud-free areas, only approximately 10 percent of

the total number of observation points can be used for cal-

culating the column abundances of CO2 and CH

4. Even so,

the number of data points signifi cantly surpasses the cur-

rent number of ground measuring points (currently under

200), and will serve to fi ll in areas where measurement has

not been conducted to date.

Ascending

Descending

5000km（on the Equator）Figure 6. Conceptual diagram of GOSAT observation and the satellite orbits (three days, 44 orbits)

GOSAT

10km diameter

666 km

Sunlight

GOSAT Sensors and Observation Methods 2

Band 1 Band 2 Band 3 Band 4

Spectral coverage [μm] 0.758~0.775 1.56~1.72 1.92~2.08 5.56~14.3

Spectral resolution [cm-1] 0.6 0.27 0.27 0.27

Target species O2 CO2 · CH4 CO2 · H2O CO2 · CH4

Instantaneous field of view/ Field of observation view at nadir

Instantaneous fi eld of view: 15.8 mradField of view for observation (footprint): diameter of app. 10.5 km

Single-scan data acquisition time

1.1, 2.0, 4.0 seconds

* 1 μm = 1/1000 mm

Table 1. Specifications of the Fourier Transform Spectrometer (FTS) sensor

Table 2. Specifications of the Cloud and Aerosol Imager (CAI) sensor

Band 1 Band 2 Band 3 Band 4

Spectral coverage [μm]

0.370~0.390 (0.380)

0.668~0.688 (0.678)

0.860~0.880 (0.870)

1.56~1.68 (1.62)

Target substances Cloud, Aerosol

Swath [km] 1000 1000 1000 750

Spatial resolution at nadir [km]

0.5 0.5 0.5 1.5

4

Analysis Methods of GOSAT data

The data taken by the FTS and CAI sensors

will be processed as shown in Figure 7. FTS-observed

values provide spectra while CAI-based data will be used

to generate cloud and aerosol information. These data

will be combined together to calculate the CO2 and CH

4

column abundances at observation points with no or only

thin clouds and aerosol layer present. Furthermore, an at-

mospheric transport model will be used with the obtained

distribution of column abundance of CO2 to estimate the

global distribution of CO2 fl ux as well as the three-dimen-

sional distribution of CO2 concentrations.

CO2 and CH

4 absorb light with particular wave-

lengths. Therefore, by measuring how much

light was absorbed by these molecules, the

amounts of CO2 and CH

4 existing through the

optical paths can be calculated . Fig. 8 provides

an example of spectra that are expected to be

obtained from observation by FTS. The spec-

tra structures like teeth of a comb indicate the

absorption by gases, such as CO2 and CH

4, and

the depths correlate with their column abun-

dances.

Among spectra obtained with FTS, only those

spectra with no clouds in the fi eld of view of the

FTS will be identifi ed with the use of images

from CAI. This is possible because the spatial

resolution of CAI is high enough to detect cloud contami-

nation in the fi eld of view of FTS. The spectra with no

clouds will then be analyzed using a numeric calculation

method called the retrieval method based on

the characteristics of absorption by gas, and

the column abundances of CO2 and CH

4 will be

derived. The CO2 absorption bands near 1.6μm

and 2.0 μm are quite important because they

provide us with a large amount of information

near the earth’s surface where the changes in

CO2 concentrations are most apparent. The ab-

sorption band near 14 μm is used for obtain-

ing information mainly at altitudes of 2 km and

above.

Once enough points of data are accumulated,

the acquired column abundances of CO2 and

CH4 can be averaged on a monthly and quar-

terly basis, and mapped out globally. The next step in

data processing is the estimation of the fl ux of CO2 using

the acquired column abundances of CO2. We effectively

“reverse” the atmospheric transport model to trace the

origins of the CO2 detected by GOSAT, and estimate the

fl ux of CO2 on a sub-continental scale (Fig. 5). The cur-

rent method of estimating fl ux of CO2 depends solely on

ground-based observation data, which results in signifi cant

errors in estimations for regions such as Africa and South

America, where observation points are scarce. GOSAT is

capable of acquiring observation data almost uniformly

around the globe and hence is expected to reduce errors in

estimated CO2 fl ux. Furthermore, using the distribution of

CO2 fl ux obtained

in this manner and

the atmospheric

transport model, it

will be possible to

simulate the global

distribution of CO2

in three dimen-

sions.

Interferogram

Cloud/aerosol distribution

SpectrumTANSO-FTS sensor

(provided by JAXA)

TANSO-CAI sensor (provided by JAXA)

CO2 flux

April August

355 357 359 361 363 365 367 369 371 373 (ppm)

? Low density High density ?

Sensors Processed productsObservation data

3D distribution of CO2

Column abundances of CO2 and CH4

Rad

ianc

e(W

/m2 /

mic

ron/

str)

0 30 60 90 120 150 180 210 240 270 300 330 360Longitude(deg.E)

-90

-45

0

45

90

Latit

ude(

deg.

N)

FTS SWIR Pseudo DataSun Zenith Angle = 80 deg. Count = 26346

Copyright (c) 2007 NIES

Wavelength(μm)

3

2

1

01.6 1.7

Figure 7. Outline of GOSAT data processing

Analysis Methods of GOSAT data3

6 8 10 12 140

2

4

6

8

10

5 7 9 11 13 15

2000 1500 1200 1100 1000 900 800 700

Wavenumber (cm-1)

Rad

ianc

e(W

/m2 /

mic

ron/

str)

Rad

ianc

e(W

/m2 /

mic

ron/

str)

Wavelength (μm) Wavelength (μm) Wavelength (μm)

Band 2 Band 3

2000015000 12000 10000 8000 7000 6000 5000 400020

15

10

5

00.5 1.0 1.5 2.0 2.5

10

0

3

2

1

0

1

0

13200cm-1 12900cm-1 6400cm-1 5800cm-15200cm-1 4800cm-1

0.76 0.77 1.6 1.7 1.95 2.00 2.05

Band 1

Rad

ianc

e(W

/m2 /

mic

ron/

str)

Wavenumber (cm-1)

Wavelength (μm)

Wavelength (μm)Band 4

O2

CO2CH4

H2OCO2 CO2

CO2 CO2H2O CH4

Absorption band of water vapor(H2O)Absorption band of carbon dioxide(CO2)Absorption band of methane(CH4)Absorption band of oxygen(O2)Absorption band of ozone(O3)

O3

H2O CO2

Figure 8. Examples of spectra obtain-

able through GOSAT ob-servation and the absorption bands of CO2

and CH4


Evaluation of Data Analysis Methods and Validation of Products

The GOSAT Project conducts research

on analytical methods for decreasing uncertainty in

the calculation of column abundances and evalu-

ates the validity of the methods by conducting simu-

lations. Furthermore, we are planning to validate

the analytical methods and the products processed

from GOSAT data after the satellite is launched.

Based on the results of the validation, we will con-

duct further research into improving our methods.

We have already performed a number of

experiments to simulate satellite observa-

tion. One example of these simulations

involved retrieving CO2 concentration by

installing a Fourier transform spectrom-

eter, which functions on the same princi-

ples as TANSO-FTS, near the top of Mt.

Tsukuba at an altitude of approximately

800 m and observing the sunlight refl ected

on the farmland at the foot of the mountain

(Fig. 9). At the same time, a small aircraft

with CO2 and CH

4 in-situ instruments took

aerial measurements between the near-

ground level of the farmland and an alti-

tude of 3,000 m. The results of these two

observations were compared and found

to be basically in agreement,

proving the reliability of our

method of evaluating the CO2

column abundance. Further

simulation tests are planned

on an ongoing basis so as to

assess and improve the anal-

ysis methods.

After the launch, the GOSAT

data will be processed into

products which will provide

information on CO2 and CH

4

columns, CO2 fl ux, and the

3D distribution of CO2 (Fig.

7). These products will be

verifi ed and evaluated us-

ing highly accurate data

independently obtained by

ground platforms or aircraft

(Fig. 10). The column abundances of CO2 and CH

4 will

be compared to observation data taken by high-resolu-

tion Fourier transform spectrometer or by direct obser-

vation using the instruments installed on the ground or

in aircraft, while cloud and aerosol data will be validated

using ground-based remote sensing instruments such as

lidar or a sky radiometer. The amounts of CO2 fl ux and

3D distribution of CO2 will also be evaluated.

Figure 9. Outline of simulation tests conducted at Mt. Tsukuba in 2005

Mt.Tsukuba

Max.3,000ｍ

CO2CH4

instrumentinstrument

in-situin-situ

Farmland

FTS

Evaluation of Data Analysis Methods and Validation of Products4

Figure 10. Schematic illustration of post-launch product validation experiments

GOSAT

FTS onboard the airplane

Sky radiometer

Ground-basedhigh-resolution FTS

Lidar

Aerosols Concentration measurement at various altitudes

Laser beam

onboard the airplaneIn-situ instrument

In-situ instrument installed at the terrestrial station

Scattered light

6

Data Distribution

NIES has been developing the GOSAT

Data Handling Facility (DHF), which will process

GOSAT data (Fig. 11). After data reception and Level

1 processing by JAXA, GOSAT observation data will

be transferred to the GOSAT DHF via Tsukuba WAN, a

high-speed network in Tsukuba. At the GOSAT DHF,

the GOSAT data and reference data from other sources

will be used to generate the column abundances of CO2

and CH4, CO

2 fl ux, and the 3D distribution of CO

2 with

the cooperation of external computing centers.

Table 3 shows the standard products that the GOSAT

DHF will provide. Level 1 data to be provided by

JAXA (L1B of FTS observation) and higher-level prod-

ucts to be generated by NIES (L1B and L1B+ of CAI

and L2, L3, L4A and L4B of FTS) will be available for

use and searching by the general public by accessing the

GOSAT DHF via networks. The provision of GOSAT

products to the general public is scheduled for after the

validation phase following the launch of the satellite.

In addition, the GOSAT DHF will compile observation

requests from users and forward them to JAXA.

Data Distribution5

Figure 11. Workfl ow of GOSAT data processing

NIES/DHFGOSAT Data Handling Facility

Data at each level

L1data

L2,L3,L4data

Validation and experiment data

Data users

Computing center Computing center

Entities providing validation and

experiment data

Entitiesproviding

reference data

JAXA

Computationresults

Input data,parameters

Computationresults

Input data,parameters

Referencedata

(From JAXA Website)

Product Level Sensor Description

L1B FTS Spectrum data obtained by the Fourier transform of interferogram data

CAI Radiance data including parameters for band-to-band registration and geometric correction (before map projection)

L1B+ CAI Radiance data including parameters for band-to-band registration, geometric correction and map projection

L2 FTS CO2 column abundances (TBD)

CH4 column abundances (TBD)

L3 FTS CO2 column concentrations projected on a map (Monthly and quarterly averages)

CH4 column concentrations projected on a map (Monthly and quarterly averages)

L4A - Amount of CO2 fl ux per region, for each of 64 regions (Monthly averages)

L4B - CO2 global distribution data (3D, Monthly averages)

Table 3. Standard products to be provided by the GOSAT DHF. See Figure 7 for how each product type will be generated

Organization and Schedule

GOSAT is scheduled to be launched

in early 2009, with full-fl edged data acquisition to

start three to six months after the launch.

NIES has formed a project unit (Fig. 12) for carry-

ing out the GOSAT Project. This unit will develop

methods for calculating the CO2 and CH

4 column

abundances from the GOSAT data, develop mod-

els for estimating CO2 fl ux, validate and evaluate

the results. At the same time, it will develop and

operate the GOSAT DHF which will process the

data, and provide information to users.

Figure 12. GOSAT Project at NIES (as of March 2008)

(Project promotion)(Climate Change Research Project)

Development of data processing techniques

Ground- and aircraft-based experiments for validation

Development of carbon balance models

Osamu Uchino, Manager Validation

Computing centers, method development, validation, research on data utilization, etc.

Cooperative organizations outside NIES

Validation, research on data utilization, etc.

Cooperative sections in NIES

Center for Global Environmental Research

Tatsuya Yokota, LeaderNIES GOSAT Project

CooperationCore Research Project 2

Public relations, other activities

Development and operation of DHF

Hiroshi Watanabe, Office Manager

Tatsuya Yokota, LeaderShamil Maksyutov, Sub-leader

NIES GOSAT Project Office

Yasuhiro Sasano, Director

Organization and Schedule6

GOSAT Project

環境省

Ministry of the Environment

独立行政法人　国立環境研究所

National Institute for Environmental Studies

独立行政法人　宇宙航空研究開発機構

Japan Aerospace Exploration Agency

Published by the Center for Global

Environmental Research, National

Institute for Environmental Studies

2008.5. 2000

For more information, please contact:

GOSAT Project Offi ce

Center for Global Environmental Research

National Institute for Environmental Studies

16-2 Onogawa, Tsukuba-shi, Ibaraki

305-8506 Japan

TEL: +81-29-850-2966 FAX: +81-29-850-2219

E-mail: [email protected]

URL: http://www.gosat.nies.go.jp/index_e.html

Documents

Global Greenhouse Gas Observation by Satellite