Simulation of aerosol height retrieval using hyperspectral data from satellite measurement

Both aerosol amount and its vertical distribution are known to play important roles in aerosol contributions to atmospheric radiations. A previous study (Joseph et al., 2008) revealed that the outgoing radiance at top of atmosphere (TOA) varies depending on aerosol vertical distribution. Recently, several investigations have been successfully carried out to derive aerosol vertical distributions using the oxygen dimer (O2-O2) column density information obtained from ground based measurements. We investigated possibilities of utilization of O2-O2 information as a tool to identify aerosol heights from space born sensors through sensitivity studies of O2-O2 column density to aerosol amounts and vertical distributions using hyper-spectra simulated at top of atmosphere (TOA). Viewing geometry, aerosol properties (e.g. refractive indices, size distribution), and aerosol optical depth (AOD) at 500 nm were used as input parameters for RTM simulations of radiances at TOA from 300 to 630 nm. Box shaped aerosol layers with 1 km vertical resolution were used to construct various cases of aerosol vertical distributions. A relative difference in radiances simulated under the conditions of 1.0 and 6.0 km aerosol layers with AOD (500 nm) of 5.0, is smaller than 5.0% in a visible (VIS) range while it is larger than 10.0% in an Ultra Violet (UV) range. The difference at 340 nm was enhanced by 30%. Sensitivity of AOD, however, is stronger in the VIS range than that in the UV range. Relative differences in AOD (500 nm) of 1.0 and 5.0 are lower than 10.0% in UV but higher than 15.0% in the VIS range. O2-O2 column densities were retrieved from those simulated radiances using the Differential Optical Absorption Spectroscopy (DOAS) technique. Sensitivities of O2-O2 column densities to the aerosol height are presented at the absorption bands of 360, 380, 476, and 577 nm, respectively.