global greenhouse gas observation by satellite
TRANSCRIPT
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
3 Greenhouse gases Observing SATellite Project
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
5 Greenhouse gases Observing SATellite Project
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