橡 GCOM (Global Change Observation Mission)

GCOM (Global Change Observation Mission)

1. Background

In the late 20th century, it has been pointed out that changes of the globalenvironment could alter the living environment for mankind. Such globalenvironmental changes include climatic warming, rise of the sea level, decrease offorests, desertification, depletion of the ozone layer, acid rain and the decreaseddiversification of species. What makes global environmental changes different fromconventional natural fluctuations is that many of them have been taking place due toman-made causes. Although these changes have not yet reached the stage of directlyaffecting the life of mankind, there is a possibility that they will have major impacts inthe 21st century.

For the protection and survival of mankind’s future generations, it is essentialto predict the future courses of these global environmental changes so that efforts canbe made to eliminate or at least reduce the adverse impacts of these changes. It must besaid, however, that the prediction of global environmental changes is extremelydifficult. In the case of the notion of global warming caused by an increase of theatmospheric CO2, while most scientists agree with the general concept, there is nocommonly agreed quantitative prediction of how and when this phenomenon willmanifest itself.

The reasons for this lack of a common prediction lie with the extreme diversityof the factors determining the global climate and the complicated interaction of thesefactors on which little scientific knowledge has yet been established. For example, onlythe approximate distribution is known in the case of clouds even though clouds are saidto significantly affect the climate. There are many unsolved issues, including the globalcloud distribution by altitude, the reason for the seemingly global stability of cloudcoverage at the present level and the cloud formation and disappearance processes.Neither is there sufficient understanding of the global distribution of aerosols whichare said to have the effect of lowering the atmospheric temperature. These are only afew of the as yet unsolved questions. Any adequate understanding of globalenvironmental changes must be based on an approach which regards the earth as asingle system within which various global geophysical parameters, processes affectingeach parameter and the interaction between parameters are understood.

The establishment of various global geophysical parameters usingconventional observation and measurement methods primarily based on fieldcampaigns, however, has been found to be extremely difficult if not impossible. Assatellite observation is capable of gathering data on various geophysical parameters ina truly global and constant manner, it makes those types of observation, which areimpossible by field campaigns possible. This clearly indicates that satellite observationis essential for any attempt to solve global environmental problems.

When an attempt is made to measure a geophysical parameter from a satellite,one type of sensor may not necessarily be sufficient to measure the said geophysicalparameter. In the case of observing a phenomenon at sea or a land area, theelectromagnetic waves from the surface are subject to absorption and scattering by theatmosphere before reaching the satellite sensor. Because of this, the combination of asensor designed to measure electromagnetic waves with a sensor designed to measurethe atmosphere often plays an important role in improving the measurement accuracywhen the measurement subject is either the sea or a land area. It is also true to say thatmany phenomena relating to the global environment involve a number of interactions.Facing such a situation, it is essential to simultaneously measure all of the geophysicalparameters affecting these interactions. In the case of the measurement of the energyflux between the atmosphere and the sea, it is necessary to measure four geophysicalparameters, i.e. sea wind velocity, sea surface temperature, atmospheric temperatureimmediately above the sea surface and water vapour. To make it possible to conduct therequired measurement, a satellite with multiple sensors must be launched and themeasurements conducted by these sensors must be integrated.

Global environmental changes are not only due to man-made causes but also tonatural fluctuations. Long-term observation covering the period of natural fluctuationsis essential in order to distinguish the natural fluctuation components from man-madecomponents. It is against this background that the NASDA has been continuouslydeveloping the ADEOS II with a view to its launch in fiscal 2000, following the launchof the ADEOS in 1996.

Satellite observation alone is not totally sufficient to elucidate all phenomenarelating to the global environment. Satellite observation can only achieve its objectivesthrough its combination with field campaign efforts, including the calibration andvalidation of the geophysical parameter data measured by sensors, observation ofphenomena (for example, deep sea and underground phenomena) which cannot bemeasured by a satellite and the development of a model which is capable of relating thegeophysical parameter data observed by a satellite to actual phenomena.

The present document describes the mission concept as well as components ofthe GCOM to achieve such objectives.

2. GCOM Mission Concept

2.1 Subjects of GCOM

The GCOM aims at continuing and improving the observation conducted bythe ADEOS and ADEOS II with a view to accumulating the scientific knowledgenecessary to elucidate global environmental problems. GCOM (Global ChangeObservation Mission) is not a name of satellites but a name of a mission. The purpose ofGCOM is to continue the observation of geophysical parameters related to its missionconcept at least 15 years from the start of ADEOSII.

In regard to global warming, the GCOM intends the measurement of mostfactors involved in the energy cycle and material cycle, which are the main mechanismsdetermining climate change, and also analysis of the relevant processes. While themeasurable geophysical parameters are detailed in 2.2, the parameters directly relatedto the energy cycle are temperature, water vapour, clouds, aerosols, albedo, heatradiation from the atmosphere and estimated air-sea energy flux, etc. Within thematerial cycle, the water cycle is directly related to the energy cycle. In regard to thewater cycle, the measurement of precipitation and estimation of evaporation areimportant.

In addition to the water cycle, measurement of the carbon cycle is a key subjectregarding the material cycle. In this particular field, apart from the measurement ofsuch greenhouse gases as CO2, CH4 and O3, the GCOM aims at estimating the primaryproduction as well as carbon flux based on measurement data on land vegetation andphytoplankton.

In regard to ozone changes in the atmosphere, monitoring of the stratosphericozone, particularly ozone in the polar regions, will continue. Moreover, efforts will bemade to measure the tropospheric ozone which is thought to affect the acid rain andwarming processes and to analyze the ozone-related chemical processes in theatmosphere.

In regard to changes of the land environment, the measuring subjects aretropical forests and the global distribution of vegetation and its changes. In regard tothe cryosphere, the size and albedo of ice coverage and snow coverage are measuredand their interaction with the climate is analyzed.

2.2 Expected Achievements of GCOM

As a succeeding satellite in the ADEOS series beginning with the launch of thefirst ADEOS in 1996, the first generation satellites of GCOM are expected to make thefollowing achievements by the end of its mission (around 2010).

2.2.1 Measurable and Estimable Geophysical Parameters

(1) Atmosphere

o Air-sea interaction

- Energy flux

Target accuracy : approximately 10% (monthly mean)

Required geophysical parameters :

sea surface temperature;

sea surface wind velocity;

water vapour immediately above sea surface;

atmospheric temperature immediately above sea surface

Required sensors : TIR; μscat, FTIR

o Clouds

- Horizontal distribution :

type;

top height;

optical thickness

Required sensor : VNTIR

o Water vapour

- Total horizontal distribution

Accuracy : approximately 10%

Required sensor : μrad

- Three-dimensional distribution (night time; day time)

Accuracy : approximately 10% (clear sky)

Required sensors : FTIR; μsounder

o Temperature

- Vertical profile

Accuracy : 1 K - 3 K 3 - 5 layers


Accuracy : 1 K 20 layers (clear sky)

Required sensor : FTIR

o Cloud Water Content

Accuracy : 0.05 kg/m2 (sea area)


o Precipitation

Accuracy : approximately 10% (sea area)

approximately 100% (land area)


o Aerosols

- Optical thickness of sea area : global

type; optical thickness; radius distribution

o Ozone

- Vertical profile in polar regions :

global, three-dimensional distribution (every day)

Target accuracy : 2%

Required sensors : UVVIS; FTIR; IR limb sounder

o Trace Gases

- Horizontal distribution :

sink/source of GHGs

stratospheric ozone

tropospheric GHG distribution

tropospheric oxidizing gases

Required sensor : FTIR

(2) Ocean

o Ocean Colour

- Chlorophyll-a :

primary production of ocean

- Extinction constant : SS; C-DOM

- Land : ocean material flux

Required Sensor : VNIR

o Sea surface wind

- Sea surface wind vector

Accuracy : 10%

Required sensor : μscat

o Sea surface temperature

- Distribution of sea surface temperature

Accuracy : 0.5 K - 0.3 K

Required sensors : TIR; μrad

o Air-sea interaction

- Water flux (including precipitation)

Accuracy : same as precipitation for the atmosphere


(3) Land

o Vegetation

- Vegetation distribution (several tens of different vegetation types)

Accuracy : 70%

Required sensor : VNIR

- Speed of forest decrease

Accuracy :

Required sensors : VNIR; (scan SAR)

- APAR; LAI; biomass; NPP


o Land cover

- Global land cover (several tens of different categories)

- Albedo


o Hydrology

- Surface water content over non-vegetated area


o Cryosphere

- Sea ice concentration

Required sensor : μrad; μscat

- Snow cover area

Required sensor : μrad; VNSWTIR

- Wet and dry snow classification over non-vegetated area


- Water content of dry snow over non-vegetated area


- Ice cover area

Required sensors : μrad; VNSWTIR

- Snow and ice surface temperature

Required sensor : TIR

o Snow and ice surface temperature and emissivity

Required sensor : TIR

o Volcano

- Volcanic fume

Required sensor : VNTIR; UV

o Wetland

Required sensor : VNTIR

o Biomass burning

Required sensors : VNTIR; FTIR

2.2.2 Possible Contribution to Understanding of Global Changes

(1) Global Warming

o Understanding of the reality of the phenomenon: global and long-termmeasurement data on various parameters which significantly affect global warming,except for some parameters (evapotranspiration, etc.) related to the water cycle, can beretrieved.

o Separation between natural fluctuations and trends: using the data set coveringthe 15 year period from the launch of the ADEOS or the 10 year period from the launchof the ADEOS II covering one sun spot cycle and two or three ENSO cycles, it will bepossible to separate the natural fluctuation components of the climate and trends.

o Understanding of the sinks/sources of GHGs

(2) Monitoring of Atmospheric Ozone

o Monitoring of the stratospheric ozone

o Monitoring of the tropospheric ozone

(3) Change of Land Environment

o Understanding of global forest dynamism

o Understanding of snow and ice changes

2.3 Sensors Required for GCOM

The planned measuring operation by the GCOM demands a radiometercovering a wide spectrum from ultraviolet to infrared, a microwave scatterometer and amicrowave radiometer as shown in 2.2.1. In order to ensure development continuityfrom previous sensors, the following sensors are considered primary candidates toperform the required measuring operation.

< Sensor Name (Tentative) > < Candidate Provider >

SGLI (GLI follow on) NASDA

AMSR follow on NASDA

ODUS NASDA

IMG follow on NASDA/MITI

ILAS II follow on JEA

SeaWinds follow on NASA/JPL

GPS occultation NASDA/?

If satellite payload is still available after the loading of the sensors, a furtherAO will be made with a view of adding extra sensors which are deemed effective tocomplete the mission of the GCOM.

3. The First Generation Satellites of GCOM

After the assessment of ADEOS failure, NASDA has decided to use small ormedium scale satellites rather than to use large scale satellites for Earth observation.In accordance to this policy, the first generation of GCOM satellite was divided to twosatellites, called GCOM-A1 and GCOM-B1.

GCOM-A1 will have an inclined orbit and observes mainly greenhouse gases,ozone and ozone related trace gases. On the other hand, GCOM-B1 will have a sun-synchronous orbit, which will be similar to those of ADEOS and ADEOSII, and mainlyobserves geophysical parameters related to atmospheric dynamics, ocean and land.

GCOM-A1 will have the following characteristics.

Orbit : 700km altitude, 70degree inclination angle

Mass : 1-1.5 ton

Core Instruments : ODUS, ILASII F/O

Launch date : Feb. 2005

GCOM-B1 will have the following characteristics.

Orbit : 800km altitude, sun-synchronous orbit

Mass : 2-2.5 ton

Core Instruments : SGLI, AMSR F/O, SeaWinds F/O, POLDER F/O

Launch date : Aug. 2005

4. GCOM-A1 SENSORS

4.1 ODUS (Ozone Dynamics Ultraviolet Spectrometer)

4.1.1 Objectives of ODUS

The ODUS has the following main objectives.

- Global mapping of atmospheric total ozone

- Measurement of top cloud height and global mapping of atmospheric aerosols

- Measurement of nitrogen dioxide (NO2) and sulfur dioxide (SO2) as urban airpollutants

4.1.2 Specifications of ODUS

The ODUS is an ultraviolet spectrometer designed to measure total ozone andis the successor to the TOMS. Compared to the TOMS, it has the following improvedcharacteristics.

o Simultaneous measurement of scattered light spectra thanks to the adoption ofarray detectors

→accuracy increase of ozone retrieval, induction of aerosol amount

o Higher spatial resolution than TOMS

　　　→understanding of stratospheric dynamics, decrease of cloud contamination

o Addition of total NO2 measurement (400 - 420 nm band)

o Measurement of cloud top height (ring effect of 393.4, 396.9 n m)

Tentative Specifications

Type : diffraction grating spectrometer, Fasty-Ebert mounting

Optics : focal length of collimation mirror: 25 cm (TBR)

Wavelength : 306 - 420 nm

Spectral Resolution : 0.5 nm

Duration of Spectrum Measurement : 30 msec

FOV

Along Track : 1.6° (at nadir)

Cross Track : 120° (at nadir)

Cross Track Scanning Duration : less than 3.5 sec

IFOV : 1.6° x 1.6° (horizontal resolution at nadir: 20 km x 20 km)

Detector : linear array detector (228 elements)

S/N Ratio : larger than 200

On-Board Calibration

Radiance : sun diffuser (three diffusers will be used with a different duty factorand will trace the long-term trend of diffusion efficiency)

Wavelength : mercury lamp (will also trace sensitivity changes of thespectrometer using a fluorescence plate)

Polarization Sensitivity : less than 5% (use of depolarizing plate)

Data Rate : 92 Kbps (12 bits A/D) + ancillary data

Power : 70 W (max) (TBR)

Weight : less than 40 kg (TBR)

Size : 30 x 50 x 50 cm (TBR)

4.1.3 Standard Products and Higher Products of ODUS

(1) Standard Products

- Total ozone

- Optical thickness of atmospheric aerosols

- Cloud top height

(2) Optional

- NO2 and SO2 as urban air pollutants

- SO2 in volcanic eruptions

(3) Higher Level Products

- Daily global distribution of standard as well as optional products

4.2 ILAS II F/O

4.2.1 Objectives of ILAS II F/O

Since the discovery of the ozone hole, observation and research havedemonstrated that the depletion of stratospheric ozone has been caused by increase ofthe atomic chlorine density in the atmosphere due to the increased use of man-madechlorofluorocarbons (CFCs), etc. With the worldwide enforcement of restrictions on theuse of CFCs, etc., an almost leveling of the CFC, etc. density in the troposphere hasbeen reported. Consequently, the destruction of the ozone layer in the stratosphere willease after the year 2000 and it is expected that the state of the atmosphere prior to therelease of chlorofluorocarbons will gradually be restored. In order to validate theeffectiveness of the unprecedented international environmental control efforts, it willbe necessary for Japan to further promote the monitoring of and research on the ozonelayer by means of the ILAS through the ILAS II F/O.

The Framework Convention on Climate Change appeals to all of the world’scountries to strengthen their atmospheric and ocean observation and studies related toclimate change. Frequent measurement of the three-dimensional distribution of GHGsin the upper troposphere and lower stratosphere is believed to be of extremeimportance for the study of the global warming phenomenon.

4.2.2 Specifications of ILAS II F/O

The ILAS II F/O will basically inherit the functions of the ILAS II as itssuccessor and new specifications will be set for the efficient monitoring of GHGs in theupper troposphere and lower stratosphere.

Tentative Specifications

Wavelength Range : (TBD)

Channel No. Wavelength (μm)

1 6.21 - 11.76

2 3.0 - 5.7

3 12.78 - 12.85

4 0.753 - 0.784

Wavelength Resolution : almost equivalent to ILAS II (TBD)

Absolute Accuracy : 03: 1%, H2O: 5% (cloud top - 60 km)

CH4, N2O, CO2: 5% (cloud top - 40 km)

CFC 11, CFC 12: 10% (cloud top - 20 km)

HNO3, NO2: 10% (10 - 30 km)

ClONO2: 20% (15 - 30km)

pressure, temperature: 0.5% (cloud top - 60 km)

aerosols and PSC: TBD

Cooling : mechanical cooler

Weight : 130 kg (TBD)

Power : 120 W (TBD)

Size : equivalent to ILAS II (TBD), requiring heat radiation field of view for thecooling unit

Observation Direction : sunrise and sunset from the satellite

Duty : 100%

Data Rate : max 5 Mbps (TBD), 440 Mbytes/rev

Lifetime : five years

4.2.3 Standard Products of ILAS II F/O

The standard products of the ILAS II F/O will be the vertical profile (1 kminterval for the 5 - 70 km region) of the following geophysical parameters and there willbe 28 measuring points (14 points between 55°N and 72°N in the northern hemisphereand 14 points between 60°S and 85°N in the southern hemisphere) per day.

Note: The accuracy figures are targets in the altitude range in which the bestaccuracy can be obtained.

5 GCOM-B1 SENSORS

5.1 SGLI

5.1.1 Objectives of SGLI

Multi-band medium spatial resolution imagers such as the GLI and MODISare classified as general-purpose radiometers capable of serving various earthobservation missions because of their versatile application. The advancement of remotesensing technologies means that wide ranging remote sensing data is now available tomake more accurate products regarding the middle as well as lower atmosphere, ocean,land and cryosphere. In fact, any accurate product regarding a specific sphereincreasingly demands products related to other spheres. For example, atmosphericaerosol and cloud products are now important for the remote sensing of ocean colour.There are strong expectations that new products will emerge through the combinationof an imager and microwave radiometer. One example is of a high resolution visualband imager playing the important role of assisting the analysis of microwaveradiometer data as part of remote sensing activities vis-a-vis the cryosphere.

The SGLI sensor will be a multi-purpose, multi-band, medium resolution,visual infrared imager and an advanced version of the GLI. Its main characteristic willbe the possession of many channels of which the wavelength specifications and field ofview are optimized for a specific target. It will also be a stable and versatile radiometersystem through thorough systematization and size reduction and will be capable ofmany new functions, which are beyond the capability of the GLI. It is designed toconduct detailed monitoring of the ground surface as well as the middle and loweratmosphere and will be capable of measuring ocean colour, land use and vegetation,snow and ice, clouds, aerosols and water vapour, etc.

The mission of the SGLI will be the natural successor and advancement of theGLI mission. While global-scale monitoring over a long period of time is essential toobserve changes of the global environment, including global warming, associated withhuman activities, the GLI provides the opportunity to conduct such monitoring and toobtain wide ranging data in a huge quantity regarding geophysical parameters relatedto the atmosphere, ocean, land and cryosphere which should prove extremely useful forthe relevant research. The SGLI mission will inherit and further advance this globalenvironment monitoring with a view to producing data sets over some 10 years. Inregard to ocean colour and aerosols, time series data for some 13 years will be producedif the data retrieved by the OCTS is included. Analytical and modeling research tointerprete such long-term observation data will also constitute important pillars of theSGLI mission.

5.1.2 What is the SGLI?

(1) Definition

The SGLI is a general-purpose visual infrared, medium resolution radiometer.

(2) Components

The required specifications of the SGLI will depend on the specific subject forobservation. In the case of ocean colour, a tilting function will be required while thisfunction will be unnecessary for other types of observation. The required groundresolution will also depend on the specific subject. For example, the measurement ofland vegetation demands a minimum resolution of 250 m. Given these requirements,the SGLI (tentative name) will not be a single sensor and will have the followingcomponents.

a. Ocean colour imager (OCI)

b. Atmosphere and land imager (ALI)

c. Infrared imager (IRI)

5.1.3 Specifications of SGLI

(1) OCI

- The OCI will have a high S/N ratio of not less than 800 to the low input radiance inthe visible band for the measurement of ocean colour.

- The OCI will have an observation angle of ± 25° in the along-track direction toavoid sun glitter.

Tentative Specifications of OCI

Ch. No.　 Wavelength(nm)　Width(nm)　 St. Rad.　 Max. Rad.　 S/N

O1 412 10 65 130 800

O2 443 10 54 109 800

O3 490 10 43 86 800

O4 520 20 31 64 800

O5 565 20 23 47 800

O6 625 20 17 33 800

O7 680 20 12 24 1000

08 710 20 7 14 800

09 749 10 7 14 800

10　 865 20 5 9 800

Note: The unit for radiance is W/m2/sr/μm.

FOV : ± 43°

IFOV : 750 m

Quantization Number : 12 bits

Weight : TBD

Power : TBD

Data Rate : 2.31 Mbps

Duty Factor : 50% (day-time operation)

Pending Issues:

- Selection of the optimum wavelength

- Adoption of a polarisation filter

- Far wind cut-off: 10-5

(2) ALI

- The ALI will have a wide dynamic range for measurement of the atmosphereand land.

- The ALI will have three observation angles of 0° and ± 45° in the along-trackdirection.

Ch. No.　 Wavelength(nm)　Width(nm)　 St. Rad.　 Max. Rad. S/N IFOV(m)

A1 380 10 60 400 500 750

A2 400 10 60 400 500 750

A3 443 10 50 600 800 750

A4 460 10 50 650 800 750

A5 545 20 30 550 600 750

A6 678 20 12 450 400 750

A7 710 20 10 350 400 750

A8 763 8 6 350 400 750

A9 　 865 20 5 304 400 750

A10 460 50 40 624 400 250

A11 545 50 25 549 400 250

A12 678 50 15 150 400 250

A13 865 50 20 257 400 250

A14 940 20 10 200 400 750

A15 1050 20 8 203 400 750


FOV : ± 43°


Weight : TBD

Power : TBD

Data Rate : 30.12 Mbps (TBD)

Duty Factor : 50% (day-time operation)

Pending Issues:

- Selection of the optimum wavelength

- Averaging to obtain the 250 m and 750 m bands due to the use of a two-dimensional CCD (TBD)

- Compression of 250 m channel data (TBD)

- Multi-directional measurement (TBD)

- Use of a non-linear amplifier for ocean-measurement channels (TBD)

- Far wing cut-off: 10-5

(3) IRI-a

Ch. No.　 Wavelength(nm)　Width(nm)　 St. Rad.　 Max. Rad. S/N IFOV(m)

S1 1.24 0.02 5 138 400 750

S2 1.38 0.04 1.5 94 150 750

S3 1.64 0.2 5 69 150 250

S4 2.21 0.1 1.3 50 400 250


FOV : ± 43°


Weight : TBD

Power : TBD

Data Rate : to be included in ALI (TBD)

Duty Factor : 100%

(4) IRI-b (TMX)

　　　Ch. No.　 Wavelength(μm)　Width(μm) TLW DTL TST DT TMX

T1 3.7 0.3 250 0.5 300 0.1 340

T2 6.7 0.5 200 0.5 300 0.1 340

T3 7.3 0.5 200 0.5 300 0.1 340

T4 7.5 0.5 200 0.5 300 0.1 340

T5 8.6 0.5 180 0.5 300 0.1 340

T6 10.8 0.7 180 0.5 300 0.1 340

T7 12.0 0.7 180 0.5 300 0.1 340

TLW : Low standard temperature

TST : Standard temperature

TMX : Maximum temperature

DT : NEDT at standard temperature

DTL : NEDT at low standard temperature

FOV : ± 43°


Weight : TBD

Power : TBD

Data Rate : 6.45 Mbps (TBD)

Duty Factor : 100%

(5) Subjects Under Discussion for SGLI

- Two black bodies on board the IRI-b

- On-board calibration source for the OCI and ALI

- Possible unification of the OCI and ALI

- Interband registration: 0.1% (TBR)

- Sensitivity deviation between bands

o Instrument: (TBD)

o After ground processing: 0.1% (TBR)

- Overshoot and undershoot: less than 1% (TBR)

- Stray light: less than 0.015 (TBR)

- Polarization sensitivity: less than 2% (TBR)

- Absolute accuracy (3σ)

o Visible, near infrared and shortwave infrared: 3% (TBR)

o Thermal infrared: 0.1 K (TBR)

- Thermal infrared detector temperature: lower than 80 K (TBR)

- Total weight: less than 200 kg

- Total power: TBD

- Total data rate

o 40 Mbps (day-time)

o 6.6 Mbps (eclipse)

5.2 AMSR F/O

5.2.1 Objectives of AMSR F/O

The AMSR F/O will be the successor to the AMSR on board the ADEOS II andwill aim at achieving the quantitative almost all-weather measurement of the followingeight geophysical parameters.

- Column water vapour

- Column cloud water content

- Precipitation

- Sea surface temperature

- Sea wind velocity

- Ice sea distribution/density

- Snow cover

- Soil moisture

5.2.2 Specifications of AMSR F/O

Tentative Specifications (Baseline)

Type : parabolic antenna, conical scanning (TBD)

Antenna Aperture : 2 m (TBR)

Swath Width : 1,600 km (TBR)

Quantization Number : 12 bits (TBR)

Incidence Angle : 55°

Cross Polarization Characteristics : less than -20 dB

Dynamic Range : 2.7 - 340 K

Absolute accuracy : 1 - 3 K

Weight : 300 kg

Power : 400 W

Data Rate : 130 Kbps (TBD)

Frequency (GHz) IFOV (km) Band Width (MHz) NEdT (K) Quantization

6.9 50 350 0.3　　 12

　　　 10.65 50 100 0.6 12

18.7 25 200 0.6 12

23.8 25 400 0.5 12

36.5 15 1000 0.5 12

89.0 5 3000 1.0 12

50.3 10 200 1.7 12

52.8　 10 400 1.3 12

In order to improve the measurement accuracy of each geophysical parameter,the following options will be examined and feasible additions or alterations will bemade.

(1) Increase of 50 GHz bands to 3 - 4 channels

Retrieval of 2 - 3 layer vertical profile of temperature ? accuracy increase ofcolumn water vapour and cloud water content

(2) Addition of 183 GHz band

Retrieval of 3 layer vertical profile of water vapour ? accuracy increase of columnwater vapour

(3) Simultaneous observation of 22.235 and 23.8 GHz

Retrieval of 2 layer vertical profile of water vapour ? accuracy increase of columnwater vapour; one frequency each will be used in tropical zones or frigid zones

(4) Transfer of 6.025 GHz to 4.0 - 4.2 GHz band

Avoidance of interference of ground radio waves; antenna aperture should be 2.2to 2.5 m to maintain spatial resolution

5.2.3 Application of Measurement Data and Expected Results

The following three types of application will be feasible for the quantitative,all-weather type data retrieved by the AMSR F/O.

(1) Improved Weather Forecasting

All of the eight geophysical parameters mentioned earlier are essential asinitial data for weather forecasting. If this data can be input to a forecasting modelwithin two hours to one day of measurement (the time delay in input varies from onegeophysical parameter to another), the accuracy of weather forecasting is expected toimprove. The actual application fields for this data are likely to include the locationingof depressions and typhoons, etc. and evaluation of the flux exchange between theatmosphere and ocean based on sea ice data, between the atmosphere and land basedon snow and soil moisture data and between the atmosphere and ocean based on seasurface temperature and sea wind velocity data, etc. with a view to improving theaccuracy of weather forecasting.

(2) Analysis of Climate

If data on these eight geophysical parameters can continuously be retrievedover a long period of time (several years to more than a decade), it should prove usefulfor quantitative analysis of the flux exchange between the ocean and atmosphere andbetween land and the atmosphere, typical examples of which are El Nino and monsoon,and also for elucidation of the exchange mechanism.

(3) Assimilation to Climatic Models

Continuous data over a long period of time can be used as assimilation data toclimatic models. Here, the assimilation technology established in (1) above and theanalysis results of (2) above should prove useful. Through this assimilation, thereliability of climatic models is expected to improve. 3.1.2 AMSR II

5.3 SeaWinds F/O

5.3.1 Objectives of SeaWinds F/O

- Global measurement of sea surface wind velocity and wind direction

- Measurement of sea ice distribution

- Vegetation distribution

5.3.2 Specifications of SeaWinds F/O

Frequency : 13.4 GHz

Spatial Resolution : 20 km (normal mode)

20 x 2 km (high resolution mode)

Antenna : type: bifocal offset, Couder type

aperture: 1.2 x 1.5 m

rotation speed: 20 rpm

suspension: magnetic bearing

Performance

Wind Speed : range: 2 - 30 (40) m/s

accuracy: ± 2 m/s: 2 - 20 m/s; ± 10%: higher than 20 m/s

Wind Direction : ± 20° (1σ) (TBR)

Weight : 240 kg

Power : 275 W

Data Rate : 250 Kbps

Options

Simultaneous measurement with microwave radiometer

o Incidence angle: 45°, 53°, 65°

o 18, 22, 37 GHz

o Full polarimetric for 18 and 37 GHz

o 22 GHz is used for water vapour correction

5.4 POLDER F/O

5.4.1 Objectives of POLDER F/O

5.4.2 Specifications of POLDER F/O

6. Other Candidate Sensors on GCOM Satellites

6.1 IMG F/O

6.1.1 Objectives of IMG F/O

(1) Measurement of Horizontal Distribution of GHGs

Characteristic spectra of CO2, CH4, CO, N2O, H2O and O3 emerging in theatmospheric radiation spectrum in the thermal infrared region will be retrieved andthe densities will be quantized to establish the global horizontal distribution andvertical column structure of gas density.

(2) Measurement of Temperature and Water Vapour

The vertical profiles of temperature and water vapour will be measured with ahigher accuracy (temperature: 1 K, water vapour: 10%) than that of conventionalmeteorological satellites. The global measurement of these parameters will enablemonitoring of the warming phenomenon in the upper troposphere.

(3) Measurement of Microphysical and Radiation Characteristics of Cirrus

The particle distribution and infrared radiation characteristics of cirrus whichare difficult to detect by conventional sensors will be measured.

(4) Measurement of Horizontal Distribution of Total Ozone

The horizontal distribution of total ozone will be measured. A highermeasurement accuracy than that of conventional meteorological satellite sensors willbe achieved, particularly at nighttime. It will also be possible to separate thetroposphere and stratosphere components of ozone.

(5) Highly Accurate Measurement of Infrared Radiation Spectrum

The total region of the heat infrared radiation spectrum from the atmosphere,clouds, land surface or sea surface will be measured with high accuracy.

(6) Highly Accurate Measurement of Sea Surface Temperature

In the heat infrared region, the radiation spectrum will be measured in manyatmospheric transmission wave number regions to achieve the highly accuratemeasurement of sea surface temperature.

(7) Detection of Pollution Gases and Particles

Using a measurement method with high wave number resolution, trace gases(CO and others) and particles which are released by volcanic eruptions or biomassburning (field fires and slash and burn farming practices), etc. will be detected.

6.1.2 Specifications of IMG F/O

Type : Michelson-Fourier interferometric infrared spectrometer

Wave Number Resolution : 0.05 cm-1 (before apodization)

Wave Number Accuracy : 0.001 cm-1

Wavelength Range : 3μm - 16μm (TBR)

Dynamic Range : 180 - 350 K

Absolute Accuracy : long-term: 0.5 K (3σ), short-term: 0.2 K (3σ)

Stability of Laser Wavelength : 3 x 10-7

Number of Bands : 3 - 4

Focal Plane Temperature : lower than 80 K

Interband Registration : less than 0.05 pixels

IFOV : 8 km

FOV

Wide Swath : 1,000 - 1,500 km

Narrow Swath : 200 - 400 km

IMC

Motion Compensation Accuracy : less than 0.5% of IFOV (TBR)

Pointing Angle (Narrow Swath) : ±45°

On-Board Black Body and Deep Space Observation

Long Duration Observation Capability (TBD)

Duration of One Measurement : less than 3 sec (TBR)

Calibration : on-board black body, deep space

On-Board Black Body : number: TBD

emissivity: more than 0.99

Calibration Frequency : TBD

Quantization Number : 16 bits (TBR)

Data Rate : LESS THAN 2 Mbps (TBR)

BER : less than 10-8 (total)

Cloud Detector : TBD

IFOV : less than 1% of main instrument

FOV : larger than FOV of main instrument

Bands : VNIR: 3, IR: 2

Duty Cycle : 100%

Life-Time : five years (survivability after five years: more than 70%) (TBD)

Weight : less than 150 kg (TBR)

Power : less than 200 W (TBR)

Size : TBD

NESR (nW/cm2srcm-1)

Wavelength(μm)　3.3　　 4.3　　4.5　　4.7　　 7　　8　　10　　14　　 16

　　 Requirements　0.015 0.2 1 4 20 24 20 30 30

6.2 GPS Occultation

6.2.1 Objectives of Occultation Observation Using GPS

Recent years have seen growing popularity of research to retrieve verticalprofile data on temperature and water vapour by means of occultation observationusing the receiver system for the position of the satellite-borne GPS, etc. Compared toother occultation observation methods, the use of such a receiver system has theadvantage of being capable of measuring the global vertical columns of temperatureand water vapour without adding hardly any extra resources because of the largenumber of subject signal sources (18 for only the GPS) and the availability of such apositioning system on almost all earth observation satellites launched in 1998 andthereafter. Given such promising prospects, occultation observation using the GPSshould be carried out by the GCOM.

6.2.2 Specifications of GPS

Apart from the US-operated GPS (Global Positioning System), the RussianGLONASS will soon become operational as a satellite-based positioning system. TheGPS alone is believed to enable 500 measuring operations per day. Given the essentialfeature of occultation observation where the number of measuring points increaseswhen the number of signal sources increases, it is highly desirable for a receiver whichis capable of receiving both GPS and GLONASS signals to be used.

At present, the GPS-based occultation observation of the temperature mainlytakes place in the altitude range of 5 - 40 km. Above an altitude of 40 km, there areproblems concerning the accuracy of initial guess and diffraction by the ionosphericlayer. Below an altitude of 5 km, there is an occurrence of multiple paths because of thesudden change of the altitudinal gradient of the refraction index, in turn caused by achange of the water vapour amount.

Radio delay time (converted to distance) of temperature and water vapourchanges in an exponential manner vis-a-vis altitude: approximately 1 mm for analtitude of 85 km, approximately 1 cm for 70 km, approximately 1 m for 35 km,approximately 10 m for 20 km and approximately 100 m for 10 km. Depending on thetarget height, the accuracy level required of a GPS receiver considerably differs.

Considering the measurement accuracy for temperature and the expectedcontribution to meteorological and climatic research, the reasonable baselinespecification at present is a temperature measurement of 3 - 30 km in altitude.

Detailed Specifications : TBD

7 Expected Results of Multiple Sensors On Board GCOM

7.1 Preparation of Data Sets Using Multiple Sensors

One major characteristic of the ADEOS series is the mounting of many sensorsfor simultaneous measurement to retrieve geophysical parameter data, which cannotbe retrieved, by independent sensors. There are largely two targets for the use ofmultiple sensors, one of which is improvement of the measurement accuracy of eachparameter while the other is the retrieval of data on parameters which is beyond thescope of independent sensors.

7.2 Higher Accuracy of Geophysical Parameter Data by Use of Multiple Sensors

(1) Sea Surface Water Temperature: SGLI; IMG F/O; AMSR F/O

While the SGLI is the main sensor for measurement of the sea surface watertemperature, its combined use with the IMG F/O will achieve a higher accuracy ofabsolute calibration and also a higher accuracy in the retrieval of sea surfacetemperature data through measurement of the water vapour. In addition, the combineduse of the SGLI and AMSR F/O will enable measurement of the sea surfacetemperature in cloud-covered sea areas.

(2) Water Vapour: IMG F/O; AMSR F/O; SGLI; GPS

The use of the IMG F/O will enable measurement of the global vertical profileof water vapour. Its combined use with the AMSR F/O will enable water vapourmeasurement in areas covered by clouds. Moreover, the combined use of the IMG F/Oand GPS, which provides the prospect of vertical profile measurement with highresolution, will improve the accuracy of global three-dimensional water vapourdistribution data to an unprecedented level.

(3) Temperature: IMG F/O; GPS; AMSR F/O; ILAS II F/O

As in the case of water vapour, the combined use of the IMG F/O with the GPSand AMSR F/O will play a central role. In polar regions, however, the ILAS II F/O canbe expected to make a contribution.

(4) Ocean Colour: SGLI; SeaWinds F/O

It is likely that the combination of ocean colour measurement by the SGLI andwhite cap correction by the SeaWinds F/O will improve the accuracy of ocean colourmeasurement.

7.3 New Geophysical Parameters Hitherto Unretrievable by a Single Sensor

(1) Air-Sea Interaction: SGLI; SeaWinds F/O; IMG F/O; AMSR F/O

The measurement of flux requires data on the sea surface temperature, seasurface wind velocity and water vapour amount as well as temperature immediatelyabove the sea surface. Such data can be retrieved by the SGLI, SeaWinds F/O and IMGF/O.

(2) Aerosols: SGLI; ODUS

The SGLI and ODUS will measure aerosols above the ocean and landrespectively. Global aerosol distribution data can be retrieved through the combinationof this data.

(3) Clouds: SGLI; IMG F/O; ODUS

There is much hitherto unretrieved parameter data regarding clouds. TheSGLI will provide data on cloud cover, optical thickness, cloud top height, cloud toptemperature and effective diameter, etc. while the IMG F/O will provide data on cirrus.In addition, the ODUS will provide data on the cloud top height. The combination ofthis data will definitely increase the knowledge on clouds.

(4) Three-Dimensional Ozone Distribution: ODUS; ILAS II F/O, IMG F/O

The ODUS will measure the horizontal distribution of daytime total ozonewhile the ILAS II F/O will measure the vertical column of ozone in the polar regions. Inthe case of the IMG F/O, although the subject measurement areas are scattered, it canmeasure ozone in terms of several layers regardless of it being day or night. Thecombination of this data will establish the global three-dimensional ozone distribution.

(5) Cryosphere: AMSR F/O; SeaWinds F/O; SGLI

Both the AMSR F/O and SeaWinds F/O can measure the cryosphere with ahigh measurement frequency. While the SeaWinds II has better spatial resolution, thecombination of these two sensors will enable the highly accurate classification of thecryosphere. In comparison, the SGLI can conduct measurement with much betterresolution even though it is subject to occultation by clouds. The combination of thesethree sensors will enable measurement of the cryosphere with unprecedented accuracy.

Documents

橡 GCOM (Global Change Observation Mission)