Thermal and near-infrared sensor for carbon observation Fourier transform spectrometer-2 (TANSO-FTS-2) on the Greenhouse gases Observing SATellite-2 (GOSAT-2) during its first year in orbit

Abstract

Abstract. The Japanese Greenhouse gases Observing SATellite-2 (GOSAT-2), in orbit since 29 October 2018, follows up the GOSAT mission, itself in orbit since 23 January 2009. GOSAT-2 monitors carbon dioxide and methane in order to increase our understanding of the global carbon cycle. It simultaneously measures carbon monoxide emitted from fossil fuel combustion and biomass burning and permits identification of the amount of combustion-related carbon. To do this, the satellite utilizes the Thermal and Near Infrared Sensor for Carbon Observation Fourier-Transform Spectrometer-2 (TANSO-FTS-2). This spectrometer detects gas absorption spectra of solar radiation reflected from the Earth's surface in the shortwave-infrared (SWIR) region as well as the emitted thermal infrared radiation (TIR) from the ground and the atmosphere. TANSO-FTS-2 can measure the oxygen A band (0.76 µm), weak and strong CO2 bands (1.6 and 2.0 µm), weak and strong CH4 bands (1.6 and 2.3 µm), a weak CO band (2.3 µm), a mid-wave TIR band (5.5–8.4 µm), and a long-wave TIR band (8.4–14.3 µm) with 0.2 cm−1 spectral sampling intervals. TANSO-FTS-2 is equipped with a solar diffuser target, a monochromatic light source, and a blackbody for spectral radiance calibration. These calibration sources permit characterization of time-dependent instrument changes in orbit. The onboard-recalibrated instrumental parameters are considered in operational level-1 processing and released as TANSO-FTS-2 level-1 version 102102 products, which were officially released on 25 May 2020. This paper provides an overview of the TANSO-FTS-2 instrument, the level-1 processing, and the first-year in-orbit performance. To validate the spectral radiance calibration during the first year of operation, the spectral radiance of the version 102102 product is compared at temporally coincident and spatially collocated points from February 2019 to March 2020 with TANSO-FTS on GOSAT for SWIR and with AIRS on Aqua and IASI on METOP-B for TIR. The spectral radiances measured by TANSO-FTS and TANSO-FTS-2 agree within 2 % of the averaged bias and 0.5 % standard deviation for SWIR bands. The agreement of brightness temperature between TANSO-FTS-2 and AIRS–IASI is better than 1 K in the range from 220 to 320 K. GOSAT-2 not only provides seamless global CO2 and CH4 observation but also observes local emissions and uptake with an additional CO channel, fully customized sampling patterns, higher signal-to-noise ratios, and wider pointing angles than GOSAT.

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“…Various current and upcoming satellite sensors aim at measuring the atmospheric abundances of the carbon compounds carbon dioxide (CO 2 ), methane (CH 4 ) and carbon monoxide (CO). Most of the space-borne instruments such as the GOSAT series (Greenhouse Gas Observing Satellite) (Kuze et al, 2009;Suto et al, 2021), the OCO series (Orbiting Carbon Observatory) (Eldering et al, 2017), the S5P (Sentinel-5 Precursor) (Hu et al, 2018) and S5 series (Sentinel-5), the TanSat program (Yang et al, 2021) and others rely on spectrometric measurements of sunlight reflected by the Earth in the shortwave-infrared (SWIR) spectral range which lends sensitivity to the column-average dry-air mole fractions of the gases (commonly denoted by XCO 2 , XCH 4 , and XCO). In particular, the upcoming European Copernicus Carbon Monitoring mission (CO2M) (Kuhlmann et al, 2019;Sierk et al, 2019) and various missions that focus on localized targets and specific emission sectors (Strandgren et al, 2020;Jervis et al, 2021) will rely on the same measurement principle.…”

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