GOSAT-2搭載TANSO-FTS-2の熱赤外バンドによる温室効果ガス観測

抄録

Greenhouse Gases Observing Satellite (GOSAT)-2, which is the successor of GOSAT, was launched on 29^th October, 2018. Thermal And Near infrared Sensor for carbon Observation (TANSO)- Fourier Transform Spectrometer (FTS)-2 on board the GOSAT-2 has two thermal infrared (TIR) bands (Bands 4 and 5) with which to observe the vertical profiles of atmospheric temperature and greenhouse gases such as carbon dioxide (CO₂) and methane (CH₄). We adopted a non-linear maximum a posteriori (MAP) method with linear mapping to retrieve the temperature and gas concentrations. The current TANSO-FTS-2 retrieval system developed before the GOSAT-2 launch utilizes the CO₂ absorption bands at around 9, 10, and 15μm (690-750cm^－1, 790-795cm^－1, 930-990cm^－1, and 1040-1090cm^－1) to retrieve CO₂, water vapor, ozone, and temperature, and utilizes the CH₄ and N₂O absorption bands at around 7 and 8μm (1140-1370cm^－1) to retrieve CH₄, N₂O, water vapor, ozone, and temperature. The signal-to-noise ratio (SNR) values of the TIR bands of the TANSO-FTS-2 are expected to be significantly larger than those of the TANSO-FTS, which gives the TANSO-FTS-2 higher sensitivity to gas concentrations. According to a preliminary retrieval simulation, the degree of freedom (DF) of the CO₂ observations of the TIR bands of the TANSO-FTS-2 is 2.44 in low latitudes, while the DF value of the TANSO-FTS TIR CO₂ observations is 2.06 under the same atmospheric conditions. The DF values of the TANSO-FTS-2 TIR CH₄ and N₂O, observations are 3.07 and 1.84, respectively, which are much higher than those of the TANSO-FTS TIR observations (0.50 and 0.14).