Global Change Observation Mission

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-W" (nickname "Shizuku") was launched. On December 23, 2017, the second satellite "GCOM-C1" (nickname "Shikisai) was launched.

An artist's rendering of GCOM-W1.

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

GCOM-W (Global Change Observation Mission – Water "Shizuku") is the first in the GCOM 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-W was approved in 2006, and development of the satellite started in 2007 with a mission budget of 20 billion Yen (US$200 Million). Mass of the satellite is 1990 kg.[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-W 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

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-synchronous 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-C was launched on December 23, 2017 via a H-IIA rocket.

Sensors

AMSR2

AMSR2 (Advanced Microwave Scanning Radiometer 2) is an improved version of AMSR (aperture 2.0 m) on ADEOS II 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 has been extended from 3 years to 5 years.

A new microwave band, namely 7.3 GHz, has been added. The 7.3 GHz band is for duplication and calibration of 6.925 GHz band. AMSR2 continues the legacy of AMSR-E, which also observed as part of the A-Train constellation.

AMSR2 observation frequency
parameter / frequency (GHz)6.925/
7.3		10.6518.723.836.589.0comments
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

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 succeeds the 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
instrumentschannelwavelengthresolutiontarget
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

See also

References
  1. GCOM-W1 at NSSDC
  2. GCOM-W at JAXA
  3. "SHIZUKU Observation Data Acquired by AMSR2". JAXA. Retrieved 2 July 2014.
  4. "JAXA: Global Change Observation Mission – Climate (GCOM-C)". Retrieved 2 July 2014.
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