Global Greenhouse Gas Observation by Satellite - Planet Action

Global Greenhouse Gas Observation by Satellite

Greenhouse gases
Observing
SATellite
Figure 1. Overview of GOSAT (©JAXA)
The Greenhouse Gases Observing Satellite (GOSAT)
will be the world’s first satellite to observe the concentrations
Studies (NIES), and the Japan Aerospace Exploration
Agency (JAXA) (Fig. 2).
of carbon dioxide and methane, two major
greenhouse gases, from space. (Fig. 1)
MOE: Ministry of the Environment
Analyses of GOSAT observation data will make it possible
to ascertain the global distributions of carbon dioxide
(CO 2
) and methane (CH 4
) and the geographical
distribution of and seasonal and inter-annual variations
Developing sensors (in collaboration with JAXA)
Validating processed products
Contributing to international efforts to reduce carbon
emissions through scientific application of GOSAT
observation data.
in the flux (i.e., emission and absorption) of greenhouse
gases. The results of the analysis will not only contribute
to a deeper scientific understanding of the behaviors MOE
Responsibilities
Shared
of the causative agents
Managing the Science
Team and promoting
of global warming, but NIES: National
data utilization
will also provide fundamental
Institute for
information Environmental
for refining climate Studies
Developing and improving
NIES
JAXA
change prediction and
JAXA: Japan
methods to derive greenhouse
gas concentrations
Aerospace
formulating global
warming countermeasures.
from satellite and auxiliary
Exploration
The GOSAT
Agency
data
Higher-level processing,
Developing sensors (in collaboration with MOE)
Project is a joint effort validation, and distribution of data products to external
parties
Developing, launching and operating the satellite
of the Ministry of the
Estimating carbon fl ux using models
Environment (MOE),
Acquiring satellite observation data, including
Cooperating with JAXA activities
data reception and recording
the National Institute
Level 1 processing of data and its calibration
for Environmental
Cooperating with MOE and NIES activities
Figure 2. Role Sharing in the GOSAT Project
1 Greenhouse gases Observing SATellite Project

Goals of the GOSAT Project
1
Goals of the GOSAT Project
Emissions of CO 2
have increased drastically
over the past century as a result of the mass consumption of
fossil fuels due to the expansion of industrial activities resulting
in dramatic increases in atmospheric concentrations
of CO 2
(Fig. 3). CO 2
, which is a greenhouse gas, leads to an
increase in atmospheric temperatures. In addition to CO 2
,
species such as CH 4
, nitrous oxide (N 2
O), and halocarbons
were designated as greenhouse gases subject to restrictions
by the Kyoto Protocol; however, CO 2
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 floods
in places where precipitation is already abundant, so there
are concerns that, without intervention, significant damage
will occur.
That being the case, the global community is moving toward
reducing greenhouse gas emissions. Under the United
Nations Framework Convention on Climate Change, the
Kyoto Protocol, which defines targets for emission reductions
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 accurate
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 flux of greenhouse gases on
a subcontinental basis (several thousand kilometers square).
This is expected to help contribute to environmental administration
efforts such as ascertaining the amount of CO 2
absorbed
or released per region and evaluating the carbon balance
in forests. Furthermore, by engaging in research using
the GOSAT data, we will accumulate new scientific knowledge
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 earthobserving
satellite technologies, develop new methodologies
to measure greenhouse gases, and promote the technological
development necessary for future earth-observing satellites.
CO 2 concentration (ppm) N 2 O concentration (ppb)
400
350
300
Carbon dioxide (CO 2 )
Methane (CH 4 )
Nitrous oxide (N 2 O)
2000
1800
1600
1400
1200
1000
800
250
0 500 1000 1500
600
2000
Year
Figure 3. Changes in concentrations of primary greenhouse
gases in the atmosphere (Modified from the IPCC
Fourth Assessment Report)
Halocarbons
13%
Nitrous oxide
(N 2 O) 6%
Methane
(CH 4 )
18%
Carbon dioxide
(CO 2 )
63%
Figure 4. Contributions of the primary greenhouse gases to
the increase in air temperature
(The above figures are based on the bestestimates
of radiative forcing gases from 1750 to
2005, modified from the IPCC Fourth Assessment
Report)
(a)
February
(b)
August
Absorption
Figure 5. The data obtained through GOSAT is expected to
allow for this kind of computation of the global distribution
of CO 2 flux
(Simulation, (a) February, (b) August, carbon conversion
[gC/m 2 /day])
CH 4 concentration (ppb)
Emissions
2

GOSAT Sensors and Observation Methods
2
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 column
abundances of CO 2
and CH 4
. The column abundances
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 onboard
the satellite is called the Thermal And Near-infrared
Sensor for carbon Observation (TANSO). TANSO is composed
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 specifications
of the two sensors.
TANSO-FTS utilizes optical interference, which is induced
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 optical
path difference little by little.
Bands 1 to 3 of FTS will provide the spectra of sunlight
reflected 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 characteristics
of sunlight reflection differ greatly between land
and water surfaces. Seawater and freshwater absorb light
which makes detection of the reflection difficult. However,
in certain directions, sunlight is reflected as specular reflection
and glitters brightly, so the sensor will target such
points for observation over large water surfaces.
GOSAT
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 field
of view of FTS. When aerosols or clouds are detected,
the characteristics of the clouds and the aerosol amounts
are identified. 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 uniformly
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 calculating
the column abundances of CO 2
and CH 4
. Even so,
the number of data points significantly surpasses the current
number of ground measuring points (currently under
200), and will serve to fill in areas where measurement has
not been conducted to date.
Table 1. Specifications of the Fourier Transform Spectrometer
(FTS) sensor
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 O 2 CO 2 · CH 4 CO 2 · H 2 O CO 2 · CH 4
Instantaneous field of
view/ Field of observation
view at nadir
Single-scan data
acquisition time
* 1 μm = 1/1000 mm
Instantaneous fi eld of view: 15.8 mrad
Field of view for observation (footprint): diameter
of app. 10.5 km
1.1, 2.0, 4.0 seconds
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)
Target substances Cloud, Aerosol
Swath [km] 1000 1000 1000 750
Spatial resolution
0.5 0.5 0.5 1.5
at nadir [km]
1.56~1.68
(1.62)
Sunlight
Descending
666 km
10km diameter
Ascending
Figure 6. Conceptual diagram of GOSAT observation and the satellite orbits (three days, 44 orbits)
5000km(on the Equator)
3 Greenhouse gases Observing SATellite Project

90
45
0
-45
-90
0 30 60 90 120 150 180 210 240 270 300 330 360
Longitude(deg.E)
Copyright (c) 2007 NIES
Analysis Methods of GOSAT data
3
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 CO 2
and CH 4
column abundances at observation points with no or only
thin clouds and aerosol layer present. Furthermore, an atmospheric
transport model will be used with the obtained
distribution of column abundance of CO 2
to estimate the
global distribution of CO 2
fl ux as well as the three-dimensional
distribution of CO 2
concentrations.
CO 2
and CH 4
absorb light with particular wavelengths.
Therefore, by measuring how much
light was absorbed by these molecules, the
amounts of CO 2
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 spectra
structures like teeth of a comb indicate the
absorption by gases, such as CO 2
and CH 4
, and
the depths correlate with their column abundances.
Radiance (W/m 2 /micron/str)
Radiance(W/m 2 /micron/str)
Radiance (W/m 2 /micron/str)
Sensors
TANSO-FTS sensor
(provided by JAXA)
TANSO-CAI sensor
(provided by JAXA)
April
terly basis, and mapped out globally. The next step in
data processing is the estimation of the flux of CO 2
using
the acquired column abundances of CO 2
. We effectively
“reverse” the atmospheric transport model to trace the
origins of the CO 2
detected by GOSAT, and estimate the
flux of CO 2
on a sub-continental scale (Fig. 5). The current
method of estimating flux of CO 2
depends solely on
ground-based observation data, which results in significant
errors in estimations for regions such as Africa and South
America, where observation points are scarce. GOSAT is
August
Observation data
Interferogram
Cloud/aerosol distribution
Processed products
1.6 1.7
Wavelength(μm)
Spectrum
3D distribution of CO 2
Column abundances of CO 2 and CH 4
Radiance(W/m 2 /micron/str)
Latitude(deg.N)
3
2
1
0
FTS SWIR Pseudo Data
Sun Zenith Angle = 80 deg. Count = 26346
? Low density High density ?
355 357 359 361 363 365 367 369 371 373 (ppm)
Among spectra obtained with FTS, only those
spectra with no clouds in the field of view of the
FTS will be identified with the use of images
CO 2 flux
Figure 7. Outline of GOSAT data processing
from CAI. This is possible because the spatial
resolution of CAI is high enough to detect cloud contamination
in the field of view of FTS. The spectra with no
clouds will then be analyzed using a numeric calculation
capable of acquiring observation data almost uniformly
around the globe and hence is expected to reduce errors in
estimated CO 2
flux. Furthermore, using the distribution of
method called the retrieval method based on
Wavenumber (cm -1 )
20000 15000 12000 10000 8000 7000 6000 5000 4000
the characteristics of absorption by gas, and
20
CO 2
flux obtained
in this manner and
Absorption band of water vapor(H2O)
15
Absorption band of carbon dioxide(CO2)
the column abundances of CO 2
and CH 4
will be
the atmospheric
Absorption band of methane(CH4)
10
Absorption band of oxygen(O2)
derived. The CO 2
absorption bands near 1.6μm
transport model, it
Absorption band of ozone(O3)
5
and 2.0 μm are quite important because they
will be possible to
0
0.5 1.0 1.5
provide us with a large amount of information
Wavelength (μm)
2.0 2.5
simulate the global
13200cm
near the earth’s surface where the changes in
12900cm -1 6400cm-1 5800cm -1 5200cm
3
4800cm -1
O2
H2O CO2 CO2 CO2 distribution of CO 2
10
2
1 H2O
CO 2
concentrations are most apparent. The absorption
band near 14 μm is used for obtainsions.
1
in three dimen-
CO2
CH4
0
0
0
0.76 0.77 1.6 1.7 1.95 2.00 2.05
Wavelength (μm) Wavelength (μm) Wavelength (μm)
Band 1
Band 2 Band 3
ing information mainly at altitudes of 2 km and
Wavenumber (cm -1 )
2000 1500 1200 1100 1000 900 800 700
10
above.
H2O
8
CH4
O3 CO2
CO2 Figure 8. Examples of
6
spectra obtainable
through
4
Once enough points of data are accumulated,
GOSAT observation
and
2
the acquired column abundances of CO 2
and 0
5 6 7 8 9 10 11 12 13 14 15
the absorption
Wavelength (μm)
CH 4
can be averaged on a monthly and quar-
bands of CO
Band 4
2
and CH 4
4

Evaluation of Data Analysis Methods and Validation of Products
4
Evaluation of Data Analysis Methods and Validation of Products
The GOSAT Project conducts research (Fig. 10). The column abundances of CO 2
and CH 4
will
on analytical methods for decreasing uncertainty in be compared to observation data taken by high-resolution
Fourier transform spectrometer or by direct obser-
the calculation of column abundances and evaluates
the validity of the methods by conducting simulations.
Furthermore, we are planning to validate in aircraft, while cloud and aerosol data will be validated
vation using the instruments installed on the ground or
the analytical methods and the products processed using ground-based remote sensing instruments such as
from GOSAT data after the satellite is launched. lidar or a sky radiometer. The amounts of CO 2
flux and
Based on the results of the validation, we will conduct
further research into improving our
3D distribution of CO 2
will also be evaluated.
methods.
We have already performed a number of
experiments to simulate satellite observation.
One example of these simulations
involved retrieving CO 2
concentration by
installing a Fourier transform spectrometer,
which functions on the same principles
as TANSO-FTS, near the top of Mt.
Tsukuba at an altitude of approximately
800 m and observing the sunlight reflected
on the farmland at the foot of the mountain
(Fig. 9). At the same time, a small aircraft
with CO 2
and CH 4
in-situ instruments took
aerial measurements between the nearground
level of the farmland and an altitude
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 CO 2
column abundance. Further
simulation tests are planned
on an ongoing basis so as to
assess and improve the analysis
methods.
After the launch, the GOSAT
data will be processed into
products which will provide
Farmland
CO 2
in-situ instrument
CH 4
in-situ instrument
FTS
Mt.Tsukuba
Max.3,000m
Figure 9. Outline of simulation tests conducted at Mt. Tsukuba in 2005
Aerosols
GOSAT
FTS onboard
the airplane
Scattered light
In-situ instrument
onboard the airplane
Concentration measurement
at various altitudes
information on CO 2
and CH 4
columns, CO 2
flux, and the
3D distribution of CO 2
(Fig.
7). These products will be
verified and evaluated using
highly accurate data
independently obtained by
ground platforms or aircraft
Ground-based
high-resolution FTS
Laser beam
Lidar
Sky radiometer
In-situ instrument installed at the terrestrial station
Figure 10. Schematic illustration of post-launch product validation experiments
5 Greenhouse gases Observing SATellite Project

Data Distribution
5
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 CO 2
and CH 4
, CO 2
flux, 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 products
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.
Table 3. Standard products to be provided by the GOSAT DHF. See Figure 7 for how each product type will be generated
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 CO 2 column abundances (TBD)
CH 4 column abundances (TBD)
L3 FTS CO 2 column concentrations projected on a map (Monthly and quarterly averages)
CH 4 column concentrations projected on a map (Monthly and quarterly averages)
L4A - Amount of CO 2 fl ux per region, for each of 64 regions (Monthly averages)
L4B - CO 2 global distribution data (3D, Monthly averages)
L1data
NIES/DHF
GOSAT Data Handling Facility
Data at
each level
JAXA
L2,L3,L4
data
(From JAXA Website)
Data users
Reference
data
Input data,
parameters
Computation
results
Input data,
parameters
Computation
results
Validation and
experiment data
Entities
providing
reference data
Computing center
Computing center
Entities providing
validation and
experiment data
Figure 11. Workfl ow of GOSAT data processing
6

Organization and Schedule
6
Organization and Schedule
GOSAT is scheduled to be launched
in early 2009, with full-fledged data acquisition to
start three to six months after the launch.
NIES has formed a project unit (Fig. 12) for carrying
out the GOSAT Project. This unit will develop
methods for calculating the CO 2
and CH 4
column
abundances from the GOSAT data, develop models
for estimating CO 2
flux, 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.
Center for Global Environmental Research
Yasuhiro Sasano, Director
(Climate Change Research Project)
Core Research Project 2
Tatsuya Yokota, Leader
Shamil Maksyutov, Sub-leader
Development of data
processing techniques
Ground- and aircraft-based
experiments for validation
Development of carbon
balance models
NIES GOSAT Project
Tatsuya Yokota, Leader
Cooperation
Hiroshi Watanabe,
Office Manager
Development and
operation of DHF
(Project promotion)
NIES GOSAT Project Office
Validation
Osamu Uchino, Manager
Public relations,
other activities
Figure 12. GOSAT Project at NIES
(as of March 2008)
Cooperative sections in NIES
Validation, research on data utilization, etc.
Cooperative organizations
outside NIES
Computing centers, method development,
validation, research on data utilization, etc.
Ministry of the Environment
National Institute for Environmental Studies
GOSAT Project
Japan Aerospace Exploration Agency
For more information, please contact:
GOSAT Project Office
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: gosat-prj1@nies.go.jp
URL: http://www.gosat.nies.go.jp/index_e.html
Published by the Center for Global
Environmental Research, National
Institute for Environmental Studies
2008.5. 2000