Greenhouse gases Observing SATellite (GOSAT) of Japan is planned to be launched in
2008. GOSAT will be equipped with a FTS to monitor CO2 column
density globally. The FTS has three near infrared bands which cover 0.76 µm, 1.6
µm, and 2.0 µm spectral regions, respectively. Retrieval algorithms to estimate
CO2 and CH4 column densities from these bands data are
now being developed. We have investigated retrieval algorithms under the
non-clear sky conditions. As one of these cases, a cirrus cloud parameter
estimation was researched. The cirrus vertical profile (i.e., existing height)
is estimated from the 0.76 µm band data. Strong water vapor absorption area is included
in the 2.0 µm spectral band, so that the reflected radiance from a ground
surface is absorbed completely by H2O in this area. Thus the signal
in this area is considered as path radiance caused by the cirrus clouds
reflection, because there is little water vapor above the cirrus cloud top. By
using this signal, the cirrus optical depth can be estimated, and then column
densities of CO2, CH4 and H2O are retrieved
precisely.
Author: T. Yokota, A. Higurashi, T. Aoki, I. Morino, H. Oguma, et al (yoko at nies dot go dot jp)
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