温室効果ガス観測技術衛星（GOSAT）の熱赤外波長における二酸化炭素鉛直プロファイル導出アルゴリズム

抄録

The Greenhouse Gases Observing Satellite (GOSAT) will be launched in 2008 for global observations of greenhouse gases such as CO₂ and methane. This study examines the feasibility of retrieving CO₂ vertical profiles from spectra from 700 to 800cm^-1 (referred to as “CO₂ 15-μm band”) of the GOSAT/Thermal And Near infrared Sensor for carbon Observation (TANSO)-FTS band 4. Retrieval simulations in which the non-linear maximum a posteriori (MAP) method was applied to pseudo-spectra at CO₂ 15-μm band (signal to noise ratio of 300) showed that retrieved CO₂ profiles agreed with true CO₂ profiles to within ±1% above 800hPa without strongly depending on a priori when atmospheric conditions such as temperature were known. These simulation results confirm the validity of CO₂ retrieval at CO₂ 15-μm band of TANSO-FTS. Differences between retrieved and true CO₂ concentrations greatly increased if atmospheric data, especially temperature data, used in the retrieval included some bias and random errors; even 1K bias of temperature yielded as many as 9% bias in retrieved CO₂ concentrations. However, treating such uncertainties in atmospheric conditions as part of measurement noise and selecting retrieval channels on the basis of the information contents of CO₂ retrieval could reduce the discrepancies between retrieved and true CO₂ concentrations; the effect of bias in atmospheric conditions decreased by almost half and that of the random error decreased to be negligible. Furthermore, channel selection could cut the computational cost for the retrieval depending on the number of the selected channels. It depends on seasons and regions how many channels should be selected in the retrieval; therefore, it should be needed to examine the method of the channel selection for each atmospheric condition.