GOSAT-2/TANSO-CAI-2 Aerosol properties by Multiple wavelengths and pixels method

Greenhouse gases Observing Satellite-2 (GOSAT-2) was launched on October 29th, 2019. GOSAT-2 has two sensors, TANSO-FTS-2 (hereinafter, this is called FTS-2) and TANSO-CAI-2 (CAI-2) for greenhouse gas and cloud-and-aerosol observation, respectively. CAI-2 performs two-directional observation in forward and backward directions and makes an observation at ten bands composed of seven wavelengths at 340, 380, 443, 550, 674, 869 and 1630 nm. The spatial resolution (IFOV) is 920 m at a wavelength of 1630 nm and 460 m at the other wavelengths. CAI-2 is characterized by having two ultraviolet (UV) bands at 340 and 380 nm, which soot and dust particles have strong light absorption. It is expected that the retrieval accuracy of light absorption characteristics of aerosols can be improved. Particle size information also can be estimated from the visible and near infrared bands. Using these bands data of CAI-2, AOT, Angstrom exponent (AE), PM2.5 equivalent and BC volume fraction are derived.

Accurate retrieval of fine mode aerosol optical thickness (AOT) is necessary to calculate an equivalent value of PM2.5 from space. Therefore, an aerosol retrieval algorithm for satellite remote sensing of urban areas to improve the retrieval accuracy of aerosol properties, which is called MWPM (Multiple wavelengths and pixels method) (Hashimoto and Nakajima, 2017), was developed. The method simultaneously retrieves fine and coarse mode AOT and single scattering albedo by using several wavelengths and spatial difference of surface reflectance. The method is useful for aerosol retrieval over spatially inhomogeneous surface region like an urban area.

The algorithm has been applied to CAI-2, and aerosol optical properties, fine and coarse particle AOTs, AE, SSA and BC volume fraction has been retrieved. We show the result of aerosol properties and comparison with aerosol properties by ground-based observation such as AERONET and SKYNET, and also show a result of sensitivity test of the algorithm for preparation of PM2.5 derivation.