Retrieval of UV Aerosol Index using backscattered monochromatic radiance measured by GOSAT CAI

Abstract:

UV Aerosol Index(AI) using backscattered radiance at a single channel has been retrieved. In the current UV AI algorithm, two UV channels are used to contrast the absorbing aerosol loaded atmosphere to Rayleigh scattering condition. There have been needs to retrieve information of absorbing aerosol from a single UV channel, such as GOSAT CAI. 30-day minimum composite method, however, makes the process possible to construct the condition with the use of only single UV channel. Also, absorption by aerosol changes with respect to AOD and wavelength for different aerosol types. Therefore, single channel aerosol index(SAI) can detect absorbing aerosol qualitatively. Correlation coefficient of SAI to current UV AI indicate significant value, showing possibility of detecting highly absorbing aerosols. The application of a cloud screening makes the presence of absorbing aerosols even more clear. Radiative transfer calculations using VLIDORT were performed to test the sensitivity of SAI and UV AI to aerosol optical properties, showing that highly absorbing aerosol results in meaningful SAI. Results from dust case study in East Asia show reasonable performance of SAI for the region with single scattering albedo below 0.90. This study concludes with a comparison of SAI from GOSAT lv.1b data to OMI UVAI data, where reasonable agreement and low false detection was found for dust cases in East Asia. The SAI value of –0.2 to 0.0 from GOSAT-CAI was comparable to OMI dust threshold value of 0.7. These findings corroborate the suitability of SAI as a for detecting absorbing aerosols for satellite instrument with a single UV channel.