Aircraft Measurements for Calibration of the NIES TCCON FTSs and Comparison of the GOSAT Data Observed over Tsukuba and Rikubetsu in Japan

Abstract:

The Total Carbon Column Observing Network (TCCON) is a global network of ground-based high-resolution Fourier Transform Spectrometers (FTSs) that record direct solar spectra in the near-infrared. From these spectra, accurate and precise column-averaged dry-air mole fractions of atmospheric constituents including CO₂, CH₄, N₂O, HF, CO, H₂O, and HDO are retrieved. The National Institute for Environmental Studies (NIES) operates two TCCON FTSs at Tsukuba (36.05°N, 140.12°E) and Rikubetsu (43.46°N, 143.77°E) in Japan.

We made the aircraft measurements over Tsukuba and Rikubetsu in January 2014 to calibrate the TCCON FTSs and to compare with XCO₂ and XCH₄ retrieved from the Short-Wavelength InfraRed (SWIR) spectra of Thermal And Near-infrared Sensor for carbon Observation - Fourier Transform Spectrometer (TANSO-FTS) onboard the Greenhouse gases Observing SATellite (GOSAT). In situ NDIR (CO₂) and CRDS (CO₂ and CH₄) measurements and flask sampling (CO₂, CH₄, CO, N₂O, and so on) were conducted onboard aircraft (Beechcraft King Air 200T) operated by Diamond Air Service Inc. from about 400 m to 9500 m. In addition, cloud observation by whole-sky camera and meteorological observation with radiosondes were performed from the ground in time with each flight. CO₂ concentrations obtained from NDIR, CRDS, and flask sampling at respective heights generally agreed within 1 ppm. We calculated XCO_2, XCH₄, XCO, and XN₂O from aircraft vertical profiles and XH₂O from radiosonde measurements. Comparisons between them and TCCON data showed acceptable results on calibration for CO₂, CH₄, CO, N₂O, and H₂O of two TCCON FTSs. We also present comparisons between aircraft data and the GOSAT data.