Presentation Information
[AAS08-P32]Air mass factor calculation for deriving NO2 column amounts from GOSAT-GW/TANSO-3 observation
*Tomohiro Sato1, Tamaki Fujinawa2,1, Hyunkwang Lim2, Takafumi Sugita2, Hiroshi Tanimoto2, YASUKO KASAI3,1 (1.National Institute of Information and Communications Technology, 2.National Institute for Environmental Studies, 3.Institute of Science Tokyo)
Keywords:
Earth's atmosphere,Satellite remote sensing,GOSAT-GW,Air mass factor
The Global Observing SATellite for Greenhouse Gases and Water Cycle (GOSAT-GW) was launched in June 2025. It is the third satellite in the GOSAT series for observations of greenhouse gases (GHGs) from space. One of the two sensors equipped in GOSAT-GW is Total Anthropogenic and Natural emissions mapping SpectrOmeter-3 (TANSO-3). The TANSO-3 sensor observes nitrogen dioxide (NO2) to increase the accuracy to monitor emission source of GHGs. The GOSAT-GW/TANSO-3 could represent the world‘s first satellite-based observation to capture the distributions of these gases as imagery within a single field of view and at the same time.
The NO2 retrieval algorithm for the GOSAT-GW (GORAL-NO2) consists of three main steps as follows. First, the total slant column density (SCD) of NO2 is derived using the differential optical absorption spectroscopy (DOAS) method from the radiance spectrum observed by Band 1 of the TANSO-3. Second, the tropospheric SCD is derived by subtracting the stratospheric SCD from the total one using the NO2 profile calculated by the chemical transport model. Third, the tropospheric vertical column density (VCD) of NO2 is derived by dividing the slant column density (SCD) by the air mass factor (AMF).
In this data processing, the AMF is a major source of error in NO2 VCD derivation and is generally calculated using radiative transfer models. In GORAL-NO2, AMFs are pre-computed for expected observation conditions and stored in a Look-Up Table (LUT), since radiative transfer model is computationally expensive. The AMF values are derived by interpolating nearby values in the LUT based on the actual observation conditions. We prepared 12 LUTs for calculating AMFs, i.e., five types of aerosols and clouds for land and ocean conditions. In this presentation, we report the evaluation of the errors of AMF calculation for GOSAT-GW/TANSO-3 NO2 observation.
The NO2 retrieval algorithm for the GOSAT-GW (GORAL-NO2) consists of three main steps as follows. First, the total slant column density (SCD) of NO2 is derived using the differential optical absorption spectroscopy (DOAS) method from the radiance spectrum observed by Band 1 of the TANSO-3. Second, the tropospheric SCD is derived by subtracting the stratospheric SCD from the total one using the NO2 profile calculated by the chemical transport model. Third, the tropospheric vertical column density (VCD) of NO2 is derived by dividing the slant column density (SCD) by the air mass factor (AMF).
In this data processing, the AMF is a major source of error in NO2 VCD derivation and is generally calculated using radiative transfer models. In GORAL-NO2, AMFs are pre-computed for expected observation conditions and stored in a Look-Up Table (LUT), since radiative transfer model is computationally expensive. The AMF values are derived by interpolating nearby values in the LUT based on the actual observation conditions. We prepared 12 LUTs for calculating AMFs, i.e., five types of aerosols and clouds for land and ocean conditions. In this presentation, we report the evaluation of the errors of AMF calculation for GOSAT-GW/TANSO-3 NO2 observation.