Validation of XCH4 derived from SWIR spectra of GOSAT TANSO-FTS with aircraft measurement data
- 1National Institute for Environmental Studies (NIES), Tsukuba, Japan
- 2Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan
- 3National Oceanic and Atmospheric Administration (NOAA), Boulder, CO, USA
- 4Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA, USA
- 5Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA
- 6Jet Propulsion Laboratory/California Institute of Technology, Pasadena, CA, USA
- 7Japan Aerospace Exploration Agency (JAXA), Tsukuba, Japan
- 8Meteorological Research Institute (MRI), Tsukuba, Japan
- *now at: Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokohama, Japan
- **now at: Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, MI, USA
- ***now at: NASA Ames Research Center, Moffett Field, CA, USA
Abstract. Column-averaged dry-air mole fractions of methane (XCH4), retrieved from Greenhouse gases Observing SATellite (GOSAT) short-wavelength infrared (SWIR) spectra, were validated by using aircraft measurement data from the National Oceanic and Atmospheric Administration (NOAA), the US Department of Energy (DOE), the National Institute for Environmental Studies (NIES), the HIAPER Pole-to-Pole Observations (HIPPO) program, and the GOSAT validation aircraft observation campaign over Japan. In the calculation of XCH4 from aircraft measurements (aircraft-based XCH4), other satellite data were used for the CH4 profiles above the tropopause. We proposed a data-screening scheme for aircraft-based XCH4 for reliable validation of GOSAT XCH4. Further, we examined the impact of GOSAT SWIR column averaging kernels (CAK) on the aircraft-based XCH4 calculation and found that the difference between aircraft-based XCH4 with and without the application of the GOSAT CAK was less than ±9 ppb at maximum, with an average difference of −0.5 ppb.
We compared GOSAT XCH4 Ver. 02.00 data retrieved within ±2° or ±5° latitude–longitude boxes centered at each aircraft measurement site with aircraft-based XCH4 measured on a GOSAT overpass day. In general, GOSAT XCH4 was in good agreement with aircraft-based XCH4. However, over land, the GOSAT data showed a positive bias of 1.5 ppb (2.0 ppb) with a standard deviation of 14.9 ppb (16.0 ppb) within the ±2° (±5°) boxes, and over ocean, the average bias was 4.1 ppb (6.5 ppb) with a standard deviation of 9.4 ppb (8.8 ppb) within the ±2° (±5°) boxes. In addition, we obtained similar results when we used an aircraft-based XCH4 time series obtained by curve fitting with temporal interpolation for comparison with GOSAT data.