Global Change Observation Mission

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An artist's rendering of GCOM-W1.

GCOM (Global Change Observation Mission), is a JAXA project of long-term observation of Earth environmental changes. As a part of Japan's contributions to GEOSS (Global Earth Observation System of Systems), GCOM will be continued for 10 to 15 years with observation and utilization of global geophysical data such as precipitation, snow, water vapor, aerosol, for climate change prediction, water management, and food security. On May 18, 2012, the first satellite "GCOM-W1" (nickname "Shizuku") was launched. On December 23, 2017, the second satellite "GCOM-C1" (nickname "Shikisai) was launched.

GCOM-W1[edit]

Launch of GCOM-W1 aboard a H-IIA rocket.

GCOM-W1 (Global Change Observation Mission - Water "SHIZUKU") is the first in the GCOM-W series. Its mission is to observe the water cycle. The satellite carries the AMSR2 (Advanced Microwave Scanning Radiometer 2) instrument, the successor to the AMSR-E carried by Aqua. This microwave radiometer will observe precipitation, water vapor, wind velocity above the ocean, sea water temperature, water levels on land areas, and snow depths. GCOM-W1 was approved in 2006, and development of the satellite started in 2007 with a mission budget of 20 billion Yen (200 Million USD). Mass of the satellite is 1990kg.[1][2]. Planned lifespan is 5 years. Polar orbit (altitude 700 km) with equator crossing local time on the ascending orbit is 13:30PM +/- 00:15.

GCOM-W1 was launched on May 17, 2012 via a H-IIA rocket, and it flies in a sun-synchronous orbit as part of the "A-train" satellite constellation. It successfully began collecting data on July 4, 2012. Its planned lifespan of 5 years means that the satellite is set to operate until 2017, although JAXA hopes that it will last longer.[3]

GCOM-C1[edit]

GCOM-C1 (Global Change Observation Mission - Climate "SHIKISAI"), the first satellite in the GCOM-C series, will monitor global climate change by observing the surface and atmosphere of Earth over the course of 5 years. Through use of its SGLI (Second generation GLobal Imager) optical instrument, it will collect data related to the carbon cycle and radiation budget, such as measurements of clouds, aerosols, ocean color, vegetation, and snow and ice. From its sun-sychronous orbit (altitude 798 km), SGLI will collect a complete picture of Earth every 2-3 days with a resolution of 250-1000m, across the UV, visible, and infrared spectrums. Mass of the satellite is 2020 kg.[4] Equator crossing local time on the descending orbit is 10:30AM +/- 00:15.

GCOM-C1 was launched on December 23, 2017 via a H-IIA rocket.

Sensors[edit]

AMSR2[edit]

AMSR2 (Advanced Microwave Scanning Radiometer 2) is an improved version of AMSR (aperture 2.0 m) on ADEOSII and AMSR-E (aperture 1.6 m) on NASA's Aqua satellite. By rotating a disc antenna (diameter 2.0 m) in 1.5 s period, it scans the Earth surface along an arc of 1450 km length. Reliability is better than AMSR and AMSR-E. Planned lifetime is extended from 3 years to 5 years. Altough technical innovation is little, the accuracy is better because of improvement of calibrations.

New microwave bands, namely 7.3 GHz band and 89.0 GHz band, have been added. The 7.3 GHz band is for duplication and calibration of 6.925 GHz band. 89.0 GHz band is for precipitation and sea ice density. On the other hand, 50.3 GHz band and 52.8 GHz band have been eliminated. They had been used for air temperature monitoring. The 89.0 GHz band had been installed on AMSR-E but the accuracy was degraded because of malfunctions.

At the moment of July 2008, AMSR series is the best microwave radiometers in the world, without competing sensors.

AMSR2 observation frequency
parameter / requency (GHz) 6.925/
7.3
10.65 18.7 23.8 36.5 89.0 comments
column vapor        
column precipitable water        
precipitation    
sea surface temperature      
sea surface wind speed      
sea ice density   89 GHz is only for cloudless area
snowpack    
soil moisture  

Note: ◎ means the most important band for that purpose.

SGLI[edit]

SGLI (Second-generation Global Imager) is a multi-band optical radiometer and the successor of GLI sensor on ADEOS-II. It consists of two sensors: SGLI-VNR (an electronic scan) and SGLI-IRS (a mechanical scan). SGLI-VNR successes technology of MESSR on MOS-1, OPS/VNIR on JERS-1, AVNIR on ADEOS, and AVNIR-2 on ALOS.

The number of channels of SGLI is 19, which is much less than GLI (36 channels). This is because SGLI carefully selected the essential bands for observations.

The swath size is 1150 km for SGLI-VNR and 1400 km for SGLI-IRS. Although a little reduction from GLI (all channels were mechanical scan with 1400 km swath), it has more bands with high-resolution (250 m). Polarimetry function has been added to SGLI-VNR, which helps detection of size of aerosol particles, enabling detection of source of the aerosols.

The lesson of GLI sensor's too big and too complicated structure, SGLI is divided to two simple systems, and the number of channels have been minimized to really essential bands, aiming at better reliability and survivability.

SGLI observation channels
instruments channel wavelength resolution target
SGLI-
VNR
non-
polarization
VN1 380 nm 250 m terrestrial aerosol, atmospheric correction, ocean color, snow & ice
VN2 412 nm vegetation, terrestrial aerosol, atmospheric correction, oceanic aerosol, photosynthetic active radiation, snow & ice
VN3 443 nm vegetation, oceanic aerosol, atmospheric correction, photosynthetic active radiation, ocean color, snow & ice
VN4 490 nm ocean color (chlorophyll, suspended sediments)
VN5 530 /nm photosynthetic active radiation, ocean color (chlorophyll)
VN6 565 nm ocean color (chlorophyll, suspended sediments, colored dissolved organic matters)
VN7 673.5 nm vegetation, terrestrial aerosol, atmospheric correction, ocean color
VN8 673.5 nm
VN9 763 nm 1000 m liquid cloud geometric thickness
VN10 868.5 nm 250 m vegetation, terrestrial aerosol, atmospheric correction, ocean color, snow & ice
VN11 868.5 nm
polarization P1 673.5 nm 1000 m vegetation, terrestrial aerosol, atmospheric correction, ocean color
P2 868.5 nm vegetation, terrestrial aerosol, atmospheric correction, ocean color, snow & ice
SGLI-
IRS
short wave infrared
(SWIR)
SW1 1050 nm 1000 m liquid cloud optical thickness, particle size
SW2 1380 nm detection of clouds over snow & ice
SW3 1630 nm 250 m
SW4 2210 nm 1000 m liquid cloud optical thickness, particle size
thermal infrared
(TIR)
T1 10.8 μm 250 m surface temperature of land , ocean, snow & ice. Fire detection, vegetation water stress
T2 12.0 μm

History[edit]

In 1998, NASDA (later JAXA) started a study on a successor satellites of ADEOS 2 and {ALOS]]. In August 1999, Ministry of Education and Science's Space Development Committee approved initiation of research and development of GCOM and ozone senor ODUS. The discussion about the specifications, involving the science community, ended up with a proposal of the first mission which consisted of GCOM-A1 (ozone & green house gas monitoring satellite) and GCOM-B1 (climate change observation satellite). In parallel, the Ministry of Environment studied about SOFIS, which was a successor of the GHG sensor ILAS-II which had been on board ADEOS-2.

In April 2000, in response to the failure of launch of H-II rocket No. 8, NASDA decided to integrate GCOM and ODUS, and focus on development of tree sensors: a successor of GLI (visible and infrared multi-band radiometer for aerosol, vegetation, ocean color), a successor of AMSR (microwave radiometer for water vapor and surface temperature), and OPUS (UV sectrometer for ozone and atmospheric pollutants). Meanwhile, NASDA called for participation of foreign countries' sensors, and decided to deploy ESA's SWIFT sensor (for tracking stratosphere pollutants).


References[edit]