7th Edition (July 2016)

Global Greenhouse Gas Observation by Satellite

GOSAT
Project

Greenhouse gases
Observing
SATellite

Figure 1. Exterior view of GOSAT (©JAXA)The Greenhouse Gases Observing Satellite“IBUKI” (GOSAT) is the world’s first spacecraft tomeasure the concentrations of carbon dioxide and methane, the two major greenhouse gases, from space (Figure1). The spacecraft was launched successfully on January
23, 2009, and has now been continuing observation after
completing its five years’ nominal operation.
Through analyzing the GOSAT observational data,
scientists will be able to ascertain the global distributionof carbon dioxide (CO2) and methane (CH4), and how

the sources and sinks of these gases vary with seasons,
years, and locations. These new findings will enhancescientific understanding on the causes of global warming. Also, they will serve as fundamental information
for improving climate change prediction and establishing sound plans for mitigating global warming.
The GOSAT Project is a joint effort of the Ministryof the Environment (MOE), the National Institute forEnvironmental Studies (NIES), and the Japan Aerospace
Exploration Agency (JAXA) (Figure 2).

MOE: Ministry of theEnvironment
・Developing sensors (in collaboration with JAXA)
・Validating processed data products・Contributing to international efforts to
reduce carbon emissions through scientific application of the GOSAT observational data.

SharedResponsibilities
Managing the Science Teamand promoting data utilization

MOE

JAXA: Japan Aerospace
Exploration Agency

NIES: National Institute forEnvironmental Studies
・Developing and improving the methods
to derive greenhouse gas concentrations from satellite and auxiliary data
・Producing, validating , and distributing
the higher-level data products
・Estimating carbon fluxes using numericalmodels・Supporting the undertakings of MOE and JAXA

NIES

JAXA

・Developing sensors (in collaboration with
MOE)
・Developing, launching, and operating the satellite
・Receiving and recording the observational data
・Processing and calibrating Level 1 data
・Supporting the undertakings of MOE and NIES

Figure 2. Role Sharing in the GOSAT Project.
1

Greenhouse gases Observing SATellite ProjectGoals of the GOSAT Project1

Goals of the GOSAT ProjectDue to mass consumption of fossil fuels in the expansion of industrial activities, worldwide emissions of CO2
increased considerably during the past century. As shownin Figure 3, atmospheric CO2 concentrations are rising very
rapidly. CO2 has a potential to warm the atmosphere andhence an increase in the concentrations leads to a rise inatmospheric temperatures. CO2 and other chemical compounds, such as CH4, nitrous oxide, and halocarbons, aredesignated as greenhouse gases that are subject to emission
regulations under the Kyoto Protocol. CO2 and CH4 together account for near 90 percent of the total warming effectcaused by these gases (Figure 4). The increased amount ofgreenhouse gases in the atmosphere is thought to cause not
only rises in global average temperatures but also severe
droughts and frequent floods. Such climatic changes may
result in enormous damages.
For these reasons, the international community ismoving toward reducing greenhouse gas emissions. In
the Kyoto Protocol under the United Nations Framework
Convention on Climate Change, emissions reduction targets for developed nations were agreed in 1997 and cameinto effect in February 2005. For promoting greenhouse gas
reductions worldwide, it is essential to set rational reduction
goals based on sure projections of climate change and its
potential influences. At the same time, it is important to obtain accurate information on greenhouse gas emissions on
national basis and evaluate their reduction measures basedon that knowledge.
The primary purpose of the GOSAT Project is to estimate emissions and absorptions of the greenhouse gases ona subcontinental scale (several thousand kilometers square;
see Figure 5) more accurately and to assist environmental
administration in evaluating the carbon balance of the land
ecosystem and making assessments of regional emissions
and absorptions. Through analyzing the GOSAT data, scientists will accumulate new knowledge on the global distribution and temporal variation of the greenhouse gases, aswell as the global carbon cycle and its influence on climate.
These new findings will be utilized for predicting future climate change and assessing its impact. The Project also aims
to expand existing earth observing satellite technologies,
develop new methodologies for greenhouse gas measurement, and promote technological development necessary
for future earth-observing satellites.

Figure 3. Changes in atmospheric concentrations ofprimary greenhouse gases. (Source: IPCC Fourth
Assessment Report)

Figure 4. Contributions of primary greenhouse gases tothe increase in atmospheric temperatures. The
above figures are based on the best estimatesof radiative forcing from 1750 to 2011. (Source:
IPCC Fifth Assessment Report)

Figure 5. Sample estimates of global CO2 sources and sinks(gC/m2/day). February (upper), August (lower),
2012.
2

GOSAT Instruments and Observational Methods

2

GOSAT Instruments and Observational Methods

GOSAT observes infrared light reflected and emitted
from the earth’s surface and the atmosphere. Column
abundances of CO2 and CH4 are calculated from the observational data. The column abundance of a gas species is expressed as the number of the gas molecules ina column above a unit surface area.
GOSAT flies at an altitude of approximately 666 km
and completes one revolution in about 100 minutes. The satellite returns to the same point in space in three days (Figure 6).
The observation instrument onboard the satellite is called the
Thermal And Near-infrared Sensor for carbon Observation(TANSO). TANSO is composed of two subunits: the Fourier
Transform Spectrometer (FTS) and the Cloud and Aerosol
Imager (CAI). Tables 1 and 2 summarize the target gas species, spectral coverage, and other specifications of these two
instruments.

condition of FTS viewing direction and the position of thesun, FTS is able to catch the specular reflection of sunlighton water surface.
CAI visualizes the state of the atmosphere and theground surface during the daytime. The image data from CAI
are used to determine the cloud existence over an extended
area that includes the FTS’s field of view (FOV). When clouds
and aerosols are detected in FOV, cloud characteristics andaerosol amounts are calculated. The information is used tocorrect the effects of the clouds and the aerosols on the spectra obtained with FTS.
During the three-day period, FTS takes fifty-six thousand measurements, covering the entire globe. Since theanalysis is limited to areas under clear sky conditions, only
two to five percent of the data collected are usable for calculating column abundances of CO2 and CH4. Nevertheless,the number of data points significantly surpasses the current
number of ground monitoring stations, which is about 200.
GOSAT serves to fill out the blanks in the ground observation network.

FTS is an instrument that utilizes optical interference.
Within the instrument the incoming light is split into two
beams which propagate in separate optical paths to create
an optical path difference between the two. These beams arethen recombined to cause interference. FTS measures the intensity of the interference by continuously changing the opti- Table 1. Specifications of FTS
cal path length difference. A spectrum, which is distribution
Band 1of light intensity over a span of wavelength, is obtained via Spectral coverage (μm) 0.758-0.775
performing mathematical operation called the Fourier trans- Spectral resolution (cm-1) 0.2
form on that measured data.
Polarized lightobservation

Performed

Band 2

Band 3

Band 4

1.56-1.72

1.92-2.08

5.56-14.3

0.2

0.2

0.2

Performed Performed

Not
Performed

O2
CO2 · CH4 CO2 · H2O CO2 · CH4
FTS observes sunlight reflected on the earth’s surface Targeted gases
and light emitted from the atmosphere and the surface. The Angle of instantaneous 15.8 mrad.(corresponds to 10.5 km when projectedon the earth's surface)former is observed in the spectral bands 1 through 3 of FTS in field of view
4.0 , 2.0 , or 1.1 (depending on the scanning modeTime
necessaryforathe daytime, and the latter is captured in band 4 during both
single scanning (sec.) being used)the day and the night. Prior to reaching the detectors of the* 1 μm = 1/1000 mm
instrument, the light in the bands 1 through 3 (SWIR: ShortWavelength InfraRed) is split into two orthogonally-polar- Table 2. Specifications of CAI
ized components (P and S components) and measured indeBand 1
Band 2
Band 3
Band 4pendently. The light in the band 4 (TIR: Thermal InfraRed), Spectral coverage 0.370-0.390 0.664-0.684 0.860-0.880 1.56-1.65
however, is not split. The instrument thereby observes the (μm)(0.380)(0.674)(0.870)(1.60)
incoming light in seven different channels. The reflection Targeted substances Cloud and aerosol
character of sunlight over land and that of over water differ Swath (km)
1000
1000
1000
750
significantly. As seawater or lakes absorb the sunlight, FTS/ Spatial resolution
0.5
0.5
0.5
1.5
SWIR is not suitable to observe these areas. Under a certain at nadir (km)Figure 6. Left: schematic illustration of how GOSAT makes observations. Center: locations of ground-based monitoring stations(source: World Data Centre for Greenhouse Gases, as of October 2015). Right: Ground track of GOSAT for 3 days (44 revolutions).
3

Greenhouse gases Observing SATellite Project©Japan Aerospace Exploration Agency, JAXA

Introduction
The GOSAT Project is a joint effort of three parties: the Japan Aerospace
Exploration Agency (JAXA), the National Institute for Environmental Studies(NIES), and the Ministry of the Environment (MOE).
Thanks to the GOSAT observations in addition to the around 200* ground-based
stations existing today, the total observation points have increased, improving theretrieval accuracy of the global distribution of CO2 and CH4 concentrations and theestimation of sinks and sources as well as the estimation of seasonal/interannual
variation of sink/source distributions. These observation results are not only usefulfor research on how CO 2 and CH 4 behave, but are also utilized as basic
information for improving future climate change projections and making global
Dataobtained with FTS and CAI are processed inwarming countermeasures.
2 product)
based
Column-averaged
volumemixing ratios
CO2 and CH4 (Leveltheflow shownin Figure
7.ofAbsorption
spectraareon SWIR data under cloud-free conditions have been estimated at NIES sinceobtainedfromroutine
the data
FTSprocessing
observationaldata.
The CAI
April 2009 whenbegan, followedby estimationof theglobal distribution of CO2 and CH4 fluxes as well as their three-dimensional
data
provide information on clouds and aerosols.
distributions (Level 4 product). The Level 2 products have been re-processed by
These
data
are andused
to calculate
columnan improved
algorithm
thesetogether
version 2 products
as well as Level
4 products
have been released to the public. Thus, we are making efforts for improving theabundances
of
CO
and
CH
over
observation
points2 of information
4 provided to the data users.
accuracy and completeness

3

180˚

210˚

240˚

270˚

300˚

330˚

0˚

30˚

60˚

90˚

120˚

150˚

180˚

Methods of Analyzing GOSAT Data
60˚

30˚

30˚

0˚

0˚

-30˚

-30˚

-60˚

-60˚

-90˚

The data obtained by FTS and CAI are processed as shown in Figure 4. Theinterferogram data obtained from FTS are processed into spectra. Since spectra
include information on atmospheric absorption, CO2 and CH4 concentrations and
The spectral data are analyzed as follows. Among
their fluxes are calculated by analyzing this information. CAI provides cloudeliminate inadequate
data andto ensureof dataallinformation
spectratoobtainedwith FTS,
only
those accuracy
measured
processing. CAI also provides information on global vegetation index.

under no cloud interference within FOV are selected
for further
processing.
This screening
uses the images
GOSAT
data provisionand distribution
from CAI. Based on the absorption characteristics of the
The NIES GOSAT Project has established the Data Handling Facility (DHF) forgases,
spectraare1 processing
analyzed,byusing
a numeriroutinethe
dataselected
processing.
After Level
JAXA, GOSAT
data aretransferred to DHF via Tsukuba-WAN, a high-speed network in Tsukuba, to be
calprocessedcalculation
schemecalledtheretrievalmethod,tointo higher-level data products. Table 1 lists the standard data products
available tocolumn
the generalpublic. For more
our website
calculateabundances
ofinformation,
CO2 andplease
CH4.visit
Changes(www.gosat.nies.go.jp/index_e.html).
in CO2 concentration are most obvious near the surfaceof the earth. The CO2 absorption bands near 1.6 µm and【Contact】 GOSAT Project Office
Center for Global Environmental Research (CGER) National Institute for Environmental Studies (NIES)
2.0 μmareimportant sinceE-mail:absorptionsin these bands
Website:www.gosat.nies.go.jp/index_e.html
gosat-prj1@nies.go.jp

210˚

240˚

270˚

300˚

330˚

0˚

30˚

60˚

90˚

120˚

150˚

140˚

50˚

50˚

40˚

40˚

30˚

30˚

-90˚
180˚

130˚

180˚

140˚

150˚

Figure 2: GOSAT orbits (daytime, 3 days, 44 orbits) (left)
Figure 3: Example of GOSAT observation points over Japan and its vicinity during daytime (right)

Sensors

TANSO-FTS sensor© JAXA

where
interferencesby clouds
anddataaerosols
areData* The numberof ground-based observation
points providing
to WDCGG: World
Center for Greenhouse Gases.
small.
Sources and sinks as well as three-dimensional GOSAT
distributionsof COandandCH4 concentrations
equipment
observational
system2
are estimated using a global atmospheric transport
The observational equipment onboard GOSAT is called Thermal And
model.
Near-infrared Sensor for carbon Observation (TANSO). TANSO is composed offeature in the spectra indicates light absorption by gases
such asData
CO2 processing
and CH4, and the depression depth correlateswith column abundances (see Note 3) of Table 3).

150˚

90˚

60˚

Methods of Analyzing GOSAT Data

two sensors, a Fourier Transform Spectrometer: FTS (“TANSO-FTS”) and a Cloudand Aerosol Imager: CAI (“TANSO-CAI”).
GOSAT
observes
near-infrared
light reflectedon theinearth’s
and thermalThemoleculesof CO
and CHthe surface
atmosphere24infrared radiance emitted from the Earth to retrieve the CO 2 and CH 4
absorblightofparticular
wavelengths.
Hence,
the atconcentrations in the atmosphere. GOSAT orbits the Earth in about 98 minutes
analtitudeofapproximately
666
km
and
returns
to
the
same
orbit
after
havingamounts of CO2 and CH4 in an optical path can be calcumade 44 circulations in three days. GOSAT makes observations basically in a
lated
throughovermeasuring
howwatermuchlightspecular
is absorbed
lattice-patternland, while overit targets
reflection by
points(called “sun-glint”) where reflectance is sufficient. Figure 2 shows the global
thesemolecules.
Figure8shows
anexampleofabsorpobservation pattern and Figure 3 shows the pattern around Japan in a closer look.
Figure3 includes
thearevalidationsites suchas Tsukuba
and some
airports, wheretion
spectrathatobtained
with
FTS. The
sawtoothed
data are collected for GOSAT data validation.

130˚

90˚

Observation data

Processed productsInterferogram

Spectrum

July 2012

TANSO-CAI sensor

Radiance distribution© JAXA

Column abundances of CO2
Column abundances of CH4

Land
Ocean
Sink

3D distribution of CO2

CO2 flux

3D distribution of CH4

Ground-based
observation data

SourceCH4 flux

4: Outline of GOSAT data processing
Figure 7. Outline Figureof GOSAT
data processing.
Table 1: List of GOSAT data products

Processing Sensor/
Level
Band

as of March 2015

Product Name

Description

Unit

FTS

FTS L1B data

Radiance spectral data obtained by performing
Fourier transform on interferogram data

FTS sceneCAI

CAI L1B data

Radiance data (band-to-band and geometriccorrections applied / data mapping not performed)

CAI

CAI L1B+ data

Radiance data (band-to-band and geometriccorrections applied / data mapping performed)

Formatprovide information on the near-surface concentrations.
The absorption band around 14 μm is used for obtaining
information mainly at altitudes above 2 km.
L1B

L1B+

CAI frame

HDF5

L2 CO2 column amount CO2 column abundance data retrieved from
(SWIR)SWIR radiance spectral data

FTS
SWIR

L2 CH4 column amount(SWIR)

CH4 column abundance data retrieved from
SWIR radiance spectral data

L2 H2O column amount H2O column abundance data retrieved from
SWIR radiance spectral data
(SWIR) *1

L2

L2 CO2 profile (TIR) *2

CO2 vertical profile data retrieved from TIR
radiance spectral data

L2 CH4 profile (TIR) *2

CH4 vertical profile data retrieved from TIR
radiance spectral data

1 – multiple scans

The column abundances of CO2 and CH4 are thenaveraged on a monthly or seasonal basis and processed
into global distribution maps. The CO2 and CH4 global
distribution data are used in the estimation of sources andsinks of CO2 and CH4 on a subcontinental scale (Figure5). The sources and sinks are calculated by an inverse
modeling using an atmospheric transport model.
FTS TIR
CAI

FTS
SWIR

CAI

L4B

Cloud coverage data

L3 global CO2
distribution (SWIR)

CO2 column-averaged mixing ratio data projected
on a global map

L3 global CH4
distribution (SWIR)

CH4 column-averaged mixing ratio data projected
on a global map

L3 global reflectance
distribution

Clear-sky radiance data (composed only ofclear-sky segments from a month worth of data)

L3 NDVI

Vegetation index global distribution data(cloudy segments excluded)

L3 global radiancedistribution

L3

L4A

L2 cloud flag--

Global radiance distribution data (3 days’ worth,including data for cloudy segments)

L4A global CO2 flux

CO2 flux per each of 64 global regions(monthly average)

L4A global CH4 flux

CH4 flux per each of 43 global regions(monthly average)

L4B global CO2
distribution

Three-dimentional global distribution of CO2
concentration

L4B global CH4
distribution

Three-dimensional global distribution of CH4
concentration

CAI frame

HDF5

Global(monthly average)

GlobalLat. 30° × Lon. 60°

64 regions across the globe,
1° mesh (annual)
Text /
43 regions across the globe, Net CDF
1° mesh (annual)Global 2.5° mesh(monthly)

Net CDFThe estimation of CO2 and CH4 sources and sinks
once relied solely on ground-based observational data.
Estimation errors were particularly large in Siberia, Asia,
Africa, and South America where ground monitoring stations are located sparsely. GOSAT iscapable of collecting observational data consistently over the clear-sky regions of the globe
and hence is able to reduce errors in the estimates of their sources and sinks. Further, using
these source and sink distribution data of CO2
and CH4 and the atmospheric transport model,
the global distributions of CO2 and CH4 in three
dimensions are simulated.
*1 This product is newly defined as a standard product.
*2 “FTS TIR L2 CO2 profile” and “FTS TIR L2 CH4 profile” newly include “FTS TIR L2 temperature profile” and “FTS TIR L2 H2O profile”
correspondingly.

Figure 8.
Sample of FTS radiance spectra showing
absorption bands of CO2 and CH4. Shown in the
top panel is a model-simulated spectrum. Panels
below present FTS Level 1B radiance spectra(explained in Chapter 5).
4

Data Processing and Data Product Distribution

4

Data Processing and Data Product Distribution

The GOSAT observational data
are routinely processed at the
GOSAT Data Handling Facility(DHF), and the data products
are distributed to general users
through the GOSAT data product distribution website.
The development of the
GOSAT DHF was completed inlate 2008, and NIES has been maintaining it for the routine processing of the GOSAT data (Figure 9).
GOSAT DHF collects the specificpoint observation requests fromthe qualified researchers (explainedin Chapter 7). GOSAT DHF collates the observation requests of
NIES and transfers them to JAXA.
JAXA coordinates all observation
requests to make the satellite operational plan and performs it as aroutine task.

Registered Users

Researchers
Level 1
Data

Observation
Plan

GOSAT Data Handling Facility(NIES/GOSAT DHF)

Observation
Requests

Observation
Requests
Standard Data
Products

JAXA

Data

Higher-Level
Data Products

GOSAT
Computer System

Reference
Data

Reference Data Providers

Data
Transfer

Data Storage

Processed
data

Computing Facilities

Figure 9. Workflow of GOSAT data processing.

The FTS and CAI data collected by the satellite arereceived and processed at JAXA Tsukuba Space Center.
Then, these data are transferred to GOSAT DHF via ahigh-speed wide area network in Tsukuba. GOSAT DHF
also collects some reference data, such as meteorological
data necessary for the higher-level data processing, fromthe cooperating institutions. Using these reference data,
the FTS observation data sent from JAXA are processed
into column abundances, sources and sinks, and threedimensional distributions of CO2 and CH4. Reference
data used for validating the data products are also stored
in this facility. All together, the amount of the data archived in seven years since 2009 will be around 900
terabytes.
The GOSAT data products are distributed throughthe GOSAT Data Archive Service (GDAS), a website for
GOSAT data distribution (Figure 10). Prior user registration is required for accessing the data products, andit can be done on the User Authentication page reached

5Greenhouse gases Observing SATellite Project

Figure 10. GOSAT Data Archive Service (GDAS).
(https://data2.gosat.nies.go.jp/index_en.html)

from the Login page of GDAS. Details on the data products are listed in Chapter 5.

m

al Andsed ofCloudhermald CH 4utes athavingly in apointsglobaler look.
where

4. Thepectrans andcloud
f dataHF) forta are, to beoductsebsiteIES)

July 2012

TANSO-CAI sensor© JAXA

5

GOSAT Data Products

Radiance distribution

GOSAT Data Products

Column abundances of CO2
Column abundances of CH4

Data products distributed from GOSAT DHF
ta products) store retrieved physical quantities such as
Table 3 lists all types of the GOSAT data prodthe atmospheric concentrations of CO2 and CH4. Data
ucts provided for general users. The Level 1 data (FTS
users can download these data products by accessing
Land
Ocean
Sink
SourceLevel 1B, CAI Level 1B, and CAI Level 1B+ data) conGDAS (Figure10). Also thereGround-based
are some tools introduced
CO2 flux
3D distribution of CO2
observation data
tain spectra and radiances acquired by the satellite. The
on “Tools” of GDAS (https://data2.gosat.nies.go.jp/in3D distribution of CH4CH4 flux
higher level data products (FTS Level 2, CAI Level 2,
dex_en.html) for users to read, check, and visualize theFTS Level 3, CAI Level 3, Level 4A, and Level 4B daGOSAT data products.
Figure 4: Outline of GOSAT data processing
Table 1:beListof GOSAT
products
Table 3. List of GOSAT data products distributed/to
distributed
fromdata
GOSAT
DHF to general users (as of March 2015).
Processing Sensor/
Level
Band
L1B
L1B+

as of March 2015

Product Name

Description

Unit

FTS

FTS L1B data

Radiance spectral data obtained by performing
Fourier transform on interferogram data

FTS sceneCAI

CAI L1B data

Radiance data (band-to-band and geometriccorrections applied / data mapping not performed)

CAI

CAI L1B+ data

Radiance data (band-to-band and geometriccorrections applied / data mapping performed)

CAI frame

FormatHDF5

L2 CO2 column amount CO2 column abundance data retrieved from
(SWIR)SWIR radiance spectral data
FTS
SWIR

L2 CH4 column amount(SWIR)

CH4 column abundance data retrieved from
SWIR radiance spectral data

L2 H2O column amount H2O column abundance data retrieved from
SWIR radiance spectral data
(SWIR) *1

L2
FTS TIR
CAI
FTS
SWIR
L3
CAI

L4A

-

L4B

-

L2 CO2 profile (TIR) *2

CO2 vertical profile data retrieved from TIR
radiance spectral data

L2 CH4 profile (TIR) *2

CH4 vertical profile data retrieved from TIR
radiance spectral data

L2 cloud flag

Cloud coverage data

L3 global CO2
distribution (SWIR)

CO2 column-averaged mixing ratio data projected
on a global map

L3 global CH4
distribution (SWIR)

CH4 column-averaged mixing ratio data projected
on a global map

L3 global radiancedistribution

Global radiance distribution data (3 days’ worth,including data for cloudy segments)

L3 global reflectance
distribution

Clear-sky radiance data (composed only ofclear-sky segments from a month worth of data)

L3 NDVI

Vegetation index global distribution data(cloudy segments excluded)

L4A global CO2 flux

CO2 flux per each of 64 global regions(monthly average)

L4A global CH4 flux

CH4 flux per each of 43 global regions(monthly average)

L4B global CO2
distribution

Three-dimensional global distribution of CO2
concentration

L4B global CH4
distribution

Three-dimensional global distribution of CH4
concentration

1 – multiple scans

CAI frame

HDF5

Global(monthly average)

GlobalLat. 30° × Lon. 60°
64 regions across the globe,
1° mesh (annual)
Text /
43 regions across the globe, Net CDF
1° mesh (annual)Global 2.5° mesh(monthly)

Net CDF*1 This product is newly defined as a standard product.
*1 Thisproduct is newly defined as a standard product. (March, 2015)*2 “FTS TIR L2 CO2 profile” and “FTS TIR L2 CH4 profile” newly include “FTS TIR L2 temperature profile” and “FTS TIR L2 H2O profile”*2 “FTS correspondingly.
TIR L2 CO2 profile” and “FTS TIR L2 CH4 profile” newly include “FTS TIR L2 temperature profile” and “FTS TIR L2 H2Oprofile” correspondingly.

Notes:
1) The details on the data processing flow are presented in Chapter 3.
2) SWIR and TIR stand for Short-Wavelength InfraRed and Thermal InfraRed, respectively. SWIR radiations are detected in the
bands 1, 2, and 3 of FTS, and the band 4 captures TIR.
3) The column abundance of gas species is defined as the number of the gas molecules in a vertical unit column stretchingfrom the ground surface to the top of the atmosphere.
4) An FTS scene and a CAI frame are equivalent to 1/60 of one orbital revolution.
5) HDF5 and netCDF are the types of the data file format used for distributing the data products. HDF 5 : Hierarchical Data
Format 5 ; netCDF: Network Common Data Form.
6) NDVI stands for Normalized Difference Vegetation Index.

6

GOSAT Data Products

Level 1B and 1B+ data
The FTS Level 1B data (Figure 8) are radiancespectra that are obtained by performing the Fouriertransformation on the signals detected by FTS. The degrees to which the targeted gas species absorb the reflected and emitted light in each of the spectral bands can beseen on the data. A single data file of the FTS Level 1B
data contains the radiance spectra obtained during 1/60
of an orbital revolution (defined as “one scene”).
The CAI Level 1B data (Figure 11) are pixel-bypixel radiances, which are converted from the digitalcounts of CAI by multiplying the given calibration factors.
The CAI Level 1B+ data (Figure 12) hold the same
Level 1B radiance data, but the geographical locations of
the image pixels are corrected for the skewness causedby the topographical roughness of the ground surface
and are projected onto a map of the earth using interpolation. Each product file of the CAI Level 1B and Level
1B+ data contains the radiance data obtained during
1/60 of an orbital revolution (defined as “one frame”).

Figure 11.
CAI Level 1B data collected on July 17,2010 over the vicinity of mainland Japan.

7

Level 2 data products
The FTS SWIR Level 2 data products store thecolumn abundances of CO2 and CH4 retrieved from theradiance spectra in the band 1 through 3 of FTS. The column abundance of a gas species is defined as the numberof the gas molecule in a vertical unit column stretchingfrom the ground surface to the top of the atmosphere.
Figures 13 and 14 show the column-averaged mixing
ratios of CO2 and CH4. The column-averaged mixing
ratio of a gas species is given by dividing the column
abundance of the gas by that of dry air. For improving
the quality of the data products, the Level 2 data processing algorithm has continuously been updated. The
validation of the Level 2 data products is also ongoing(explained in Chapter 6).
The FTS TIR Level 2 data products are verticalconcentration profiles of CO2 and CH4 derived from theradiance spectra in the band 4 of FTS.
The CAI Level 2 cloud flag data product (Figure15) stores the clear-sky confidence levels that are calculated from the CAI Level 1B data.

Figure 12.
CAI Level 1B+ data collected on July 17,2010 over the vicinity of mainland Japan.

Figure 15.
CAI Level 2 cloud flag for July 17, 2010,
overlaid with CAI Level 1B data (seeFigure 11). Black indicates clouds.

Figure 13.
FTS SWIR Level 2 CO2 column abundance (2.5 deg mesh)
for August 2013 derived for cloud-free regions. Blanks inwhite denote no available data.

Figure 14.
FTS SWIR Level 2 CH4 column abundance (2.5 deg mesh)
for August 2013 derived for cloud-free regions. Blanks inwhite denote no available data.

Figure 16.
FTS SWIR Level 3 global CO2 distribution for August 2013
(in 2.5 deg mesh). Blanks in white denote data grids morethan 500 km away from the nearest GOSAT scans.

Figure 17.
FTS SWIR Level 3 global CH4 distribution for August 2013
(in 2.5 deg mesh). Blanks in white denote data grids morethan 500 km away from the nearest GOSAT scans.

Greenhouse gases Observing SATellite Project

GOSAT Data Products

Level 3 data products
The FTS SWIR Level 3 data products (Figures 16
and 17) store the monthly global distributions of CO2
and CH4 that are calculated from the FTS SWIR Level 2
column-averaged mixing ratios of CO2 and CH4. A geostatistical calculation technique called Kriging method
is applied to estimate values for blank regions in the FTS
SWIR Level 2 distributions. Values gridded into 2.5degree cells are provided.
The CAI Level 3 global radiance distribution data
product (Figure 18) is processed for every three consecutive days; the CAI radiance data collected during thedays are assembled to give a global cloud distribution
map.
The CAI Level 3 global reflectance distribution
data product (Figure 19) shows the feature of the groundsurface globally. These data are processed by selecting
the least cloudy images from the CAI data collected in amonth and consolidating them on a global map.
The Level 3 normalized difference vegetation in-dex (NDVI) (Figure 20) data are generated by contrasting the CAI radiances in band 3, which are sensitive toground surface vegetations, to those in band 2, which areless sensitive to the vegetations.

Figure 18.
CAI Level 3 global radiance distribution obtained between July 15
and 17, 2010.

Figure 19.
CAI Level 3 global reflectance distribution synthesized fromcloud-free data obtained between July 1 and 31, 2010.

Figure 20.
CAI L3 NDVI Product. Global map of normalized difference
vegetation index (NDVI) for August 2013.

Figure 21.
L4A global CO2 flux. A sample map of regional CO2 flux estimates,
August 2012.

Figure 23.
L4B global CO2 distribution. A sample map extracted from global
three-dimensional CO2 distribution, at an altitude of approx. 800
m (0.925 level on a hybrid sigma-pressure coordinate), August
2012.

Figure 22.
L4A global CO 2 flux. A sample map of regional CO 2 flux
uncertainties, August 2012.

Level 4 data products
The Level 4A data products (Figure 21, 22 for CO2)
shows monthly averaged source/sink strengths (fluxes)of CO2 and CH4 in 64 and 43 regions respectively with
their uncertainties that are inversely estimated from theFTS SWIR Level 2 column-averaged mixing ratios,
ground-based observational data, and other meteorological data such as wind direction and velocity, using a
global atmospheric transport model.
The Level 4B data products (Figure 23 for CO2)
presents global CO2 and CH4 concentrations in three dimensions calculated from the Level 4A data product using the atmospheric transport model. The data producthas a horizontal resolution of 2.5˚×2.5˚ and a time stepof six hours.

8Validation of GOSAT Data Products

6

Validation of GOSAT Data Products

In order for the GOSAT data products to be utilized
meaningfully in the science community, uncertainties associated with the data products need to beclarified through validation. High-precision data obtained independently by ground-based instruments
and aircrafts are used to validate the data products.
Improvements in the data processing algorithms
are made based on the validation results.

National Oceanic and Atmospheric Administration’s
airborne measurement program. The results of the comparison (as of May 2014) indicated that the retrieved
Level 2 CO2 and CH4 column abundances were slightly

lower than the reference values, and the latitudinal distribution pattern (i.e., zonal mean) of the Level 2 data
were broadly consistent with those of the reference values. The data product validation activities are continued,
and the results acquired are used for reference in thefurther continued improvement of the data processing
algorithms.

Validation of the GOSAT data products acquired
through the routine processing of the GOSAT observational data (Figure 7) is necessary in order for the data
products to be used meaningfully in the science community. The precision and bias of thedata products must be clarified. To this end,
the GOSAT data validation team has been utilizing high-precision reference data obtained
through ground-based and airborne measurements (Figure 24). For validating the Level 2
column abundances of CO2 and CH4, the teamuses data from ground-based high-resolution
Fourier transform spectrometers and in-situ
observation instruments installed on aircrafts.
Properties of clouds and aerosols calculated in
the routine data processing are checked against
the data obtained with remote sensing instruments such as ground-based sky radiometers
and lidars. The estimated source/sink strengths
Figure 24.
and three-dimensional distributions of CO2 andSchematic illustration of the data product validation experimentCH4 are compared with other model outputs.
As of October, 2015
The data validation team has carried out
Ny Ålesund
EurekaPoker Flat
Sodankylä
a series of data validation activities and comEast Trout Lake
Moshiri
Bialystok
Oxfordshire
pared the Level 2 data products to the groundPark Falls
Anmyeondo
Paris
BremenRikubetsu
Orléans
Edwards
Indianapolis
Heifeibased and airborne reference data. Figure 25
Tsukuba
Pasadena
~
Izana
Saga
Karlsruhe
Garmisch
Philippines
shows the sounding locations of the groundFour
Corners
based high-resolution Fourier transform
ManausLamontDarwinAscension
Islandspectrometers in the Total Carbon Column
RéunionWollongong
Observing Network and other independent
Laudersites (http://tccon.ornl.gov/). Data obtained inJapan, Europe, Oceania, and North America
Operational TCCON Sites
Future TCCON Sites
Previous TCCON Sites
have been used in these validation activities.
Figure 25.
Also, those data have been employed whichSounding locations of the ground-based high-resolution Fouriertransform spectrometers in the Total Carbon Column Observing
are collected in Japan Airlines’ CONTRAIL
Network. Sites shown in red have been used for the data validation.
(Comprehensive Observation Network forTrace gases by Airliner) project and the US
9Greenhouse gases Observing SATellite ProjectProject Information and Research Announcements

7

Project Information and Research Announcements

The latest information is posted on the GOSAT
Project website and in the Project’s newsletter.
Back issues of the newsletter are available on thewebsite. The GOSAT Project has solicited research
proposals from scientists around the world to encourage further use of the GOSAT data.
The website of GOSAT Project (Figure 26) posts
the latest news of the project as well as other information such as technical details, project results, GOSAT
research announcements, and back issues of GOSATPROJECT NEWSLETTER.
Data users can download GOSAT data products
at GDAS, the GOSAT data product distribution site
(Figure 10). There, the users can also view selected data
products plotted on global maps.
Figure 27 shows the project website of the upcoming successor GOSAT-2, where the latest information
is provided such as requirements for the spacecraft andinstruments.

Through research announcements for ten times
from 2008 to 2016, the GOSAT Project solicited research proposals from scientists worldwide in the following five research areas: instrument calibration, dataprocessing algorithm development, carbon balance estimation and atmospheric transport modeling, data validation, and data application. A total of 126 proposals has
been selected (Table 4). The lists of selected proposals
are posted on the Project website (http://www.gosat.
nies.go.jp/eng/proposal/proposal.htm). Scientists not
only in Japan but also around the world responded to
the research announcements, showing active interests in
the Project. Table 5 shows the number of the selected
research proposals per nation. The meetings of principal
investigators were held at Tokyo, Japan in 2008, Kyoto,
Japan in 2010, Edinburgh, UK in 2011, Pasadena, USA
in 2012, Yokohama, Japan in 2013, Tsukuba, Japan in
2014,Pasadena, USA in 2015, and Kyoto, Japan in 2016.
Attended scientists shared the latest information on theirresearches and discussed their progresses.
Table 4. Number of selected research proposals per research area.
2008

2009

2010

2011-16

Total

11

7

2

2

22

Data Validation

15

7

1

7

30

Source-Sink Estimation

6

8

3

0

17

Data Application

16

14

9

11

50

Calibration

4

Data Processing Algorithm

4

Data Application / Validation2

Source-Sink Estimation /Data Application
Total

2

1
52

36

18

1
20

126

Table 5. Number of selected research proposals per nation.

Figure 26. Top page of GOSAT Project Website(http://www.gosat.nies.go.jp/)

Figure 27. Top page of GOSAT-2 Project Website(http://www.gosat-2.nies.go.jp/)

CountryJapan
USA
Germany
China
CanadaFranceNetherlands
UK
RussiaFinland
Australia
India
Italy
Korea
Spain
Indonesia
BelgiumBrazilCzech
New Zealand
NorwaySingapore
Malaysia
Taiwan, ROC
Belarus
Total

2008
23
7
6
1
3
2
3
2
4

2009
8
8
2

2
1
3
2
1
2
1
1

2010
1
3
2
2
1
1

1
2
1
1
1
1

2011-16
4
4
2
3

1
1

1

1
1
1
1
1
1

1
1
1

52

36

18

1
20

Total
36
22
10
6
5
5
5
5
4
4
3
2
2
2
2
2
1
1
1
1
2
1
1
1
1
126

10

Organization and Plans

8

Organization and Plans

GOSAT has been operating properly since thespacecraft was placed in orbit on January 23, 2009. The
initial calibration and validation of the instruments onboard started three months later, and the routine observation has been continued since July 28. The distributionof the Level 1 data to the general public was initiated on
October 29 of the same year. This was followed by therelease of the Level 2 and Level 3 data products in 2010,and Level 4 products in 2012.
A project unit in NIES carries out the GOSAT
Project. This unit implements the primary tasks of the
GOSAT Project, which include developing algorithms
for calculating column abundances of CO2 and CH4 fromthe GOSAT observational data, validating and evaluating the results, and developing and improving numerical models for estimating the sources and sinks of CO2

and CH4. The unit also operates GOSAT DHF and provides information to data users (Chapter 4). In FY2016,
Satellite Observation Center was newly established tostrengthen the administrative and operational structurefor GOSAT and GOSAT-2 (Figure 28).
The CO2 and CH4 Level 4 data products have beenreleased since December 2012 and July 2014, respective-

ly. For updating the released data products, the Projectwill continue the tasks of renewing the data processing
algorithm, processing and re-processing the observational data with the improved algorithms, and validating
the acquired data products.

Figure 28. Satellite Observation Center organization(as of July. 2016).

Ministry of the Environment
環境省
National Institute for Environmental Studies

GOSAT Project

国立研究開発法人

国立環境研究所

Japan Aerospace Exploration Agency
国立研究開発法人

宇宙航空研究開発機構

For more information, please contact:
Satellite Observation Center
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: gosat-prj1@nies.go.jp
URL: http://www.gosat.nies.go.jp/index_e.html● For inquiries on the distribution of the GOSAT data products,

please visit our website at...http://data2.gosat.nies.go.jp/
or contact us at....................gosat-support@nies.go.jp

Published bySatellite Observation Center

This publication is printed on paper manufactured entirely from recycled material (Rank A) , in accordance with the Law
Concerning the Promotion of Procurement of Eco-Friendly Goods and Serviced by the State and Other Entities.

2016. 7 (Partly revised on: 2021. 6)