Abstract
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.
