Greenhouse gas concentration retrieval algorithm for spectra measured by TANSO-3 on GOSAT-GW

Abstract

The Global Observation SATellite for Greenhouse gases and Water cycle (GOSAT-GW) is planned to be launched in FY2024. Total Anthropogenic and Natural emissions mapping SpectrOmeter-3 (TANSO-3) on GOSAT-GW has three bands in the range from visible to shortwave infrared spectral regions, including the carbon dioxide (CO₂) and methane (CH₄) absorption bands. The GOSAT-GW project will provide column-averaged dry air mole fractions of CO₂ and CH₄ (XCO₂ and XCH_4, respectively) estimated from the observed spectra as the TANSO-3 Level 2 greenhouse gas (L2GHG) product. This product is processed by the algorithm called GOsat Retrieval ALgorithm (GORAL), which includes two different greenhouse retrieval techniques; the full physics and proxy methods. The full physics method simultaneously estimates XCO₂ and XCH₄ with explicit consideration of multiple scattering by aerosols in the radiative transfer calculations. The proxy method estimates XCH₄ utilizing CO₂ as a proxy to resolve contamination by multiple scattering using the close absorption bands of CO₂ and CH₄ near 1.6 μm.