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Global Change Observation Mission (GCOM) is a follow on mission of ADEOS, ADEOS2 and TRMM. It is under phase A study in JAXA (Japan Aerospace Exploration Agency). GCOM is not a series of satellites but a mission and its concept is to continuously monitor geophysical parameters which are critical to understand global change phenomena, especially phenomena related to climate change. Those parameters include, but not limited to, optical thickness of aerosols and clouds, water and energy fluxes, carbon fluxes, sink and source of greenhouse gases, etc. The measurements of geophysical parameters will continue more than 15 years after the launch of ADEOS2. The first generation satellites of GCOM after ADEOS2 is now composed of 3 satellites, i.e. GOSAT, GCOM-B1, and GPM core satellite. The target of GOSAT is to monitor tropospheric greenhouse gases and clarify sources and sinks of these gases with the aid of atmospheric inverse models. ADEOSΠwas launched on Dec., 2002. However, after about 10 months operation, it has lost most of its power due to the solar paddle failure. The exact cause of the accident is not apparent at this time, JAXA is now considering to launch a satellite as a substitute of ADEOSΠ. Up to now, candidate sensors on board this satellite is 3, i.e. GLI follow on, AMSR follow on and SeaWinds follow on. Further, ADEOSΠ F/O will be dividedd into two satellites, i.e. GCOM-C which will carry GLI F/O and GCOM-W which will carry AMSR F/O and SeaWinds F/O. The GLI F/O will be rather different from GLI. The main targets of GLI F/O are atmospheric aerosols, coastal zone and land. In order measure aerosols over both ocean and land, it will have ultra violet channels, as well as polarization and bi-directional observation capability. For, coastal zone and land observation, the IFOV of GLI F/O for these targets will be around 250m. The instrument will be composed of several components. The shorter wavelength region will adopt push broom scanners, while long wave region will use a conventional whisk broom scanner. AMSR F/O will be very similar to AMSR on ADEOSΠ and AMSR-E on EOS-Aqua. SeaWinds F/O will be also similar to SeaWinds on ADEOSΠ with some modifications. There are two options on the orbit. One is the same to that of ADEOSΠ, i.e. around 800km altitude. Another is a higher orbit to allow faster turn around. The target launch date is fiscal 2008. JAXA has other satellite series, starting from MOS-1 to JERS-1. The next satellite to follow the JERS-1 is ALOS (Advanced Land Observing Satellite), which will be launched in 2005. The mission of ALOS is to provide sufficient data, which enable to generate 1 to 25,000 scale base maps all over the world.
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