Comparisons between XCH₄ from GOSAT Shortwave and Thermal Infrared Spectra and Aircraft CH₄ Measurements over Guam

抄録

The Thermal and Near-infrared Sensor for Carbon Observation Fourier Transform Spectrometer (TANSO-FTS) on board the Greenhouse Gases Observing Satellite (GOSAT) simultaneously observes column abundances and profiles of CH₄ in the same field of view, from the shortwave infrared (SWIR) and thermal infrared (TIR) bands, respectively. We compared CH₄ column-averaged dry-air mole fractions (XCH₄) derived from the SWIR band, XCH₄ calculated from the TIR CH₄ profiles, and XCH₄ calculated from the CH₄ data obtained over Guam airport by commercial aircraft. The difference between the SWIR-XCH₄ and aircraft XCH₄ values (SWIR - aircraft) was −8 ppbv on average, and the 1σ standard deviation was 10 ppbv. The average difference between the TIR-XCH₄ and aircraft XCH₄ values (TIR - aircraft) was −5 ppbv, and the 1σ standard deviation was 15 ppbv. The ranges of uncertainties in the calculated aircraft XCH₄ values were estimated to be 9, 3, and 2 ppbv, which came from stratospheric CH₄ assumption, tropopause height determination, and meteorological dataset used, respectively. Both the SWIR- and TIR-XCH₄ values agreed within 0.5% of the aircraft XCH₄ values, demonstrating that the GOSAT CH₄ data are both valid and consistent with each other over the tropical ocean.