Retrieval of aerosol effective height using O4 band from OMI with its type detection from MODIS over East Asia

다국어 초록 (Multilingual Abstract)

Aerosol is one of the important elements in understanding the radiative forcing for the climate studies and monitoring air quality issues. For this reason, aerosol amount and its optical properties have been observed and analyzed extensively by using ground-based and space-borne measurements. These measurements have provided aerosol optical depth (AOD), single scattering albedo (SSA), and size parameters such as fine mode fraction (FMF), and ？ngstr？m exponent (AE) over long time period. Although limited in spatial coverage, active measurements such as Light Detection and Ranging (LIDAR), has provided observation on the vertical distribution of aerosol, which depends on transport path or aerosol types. However passive space-borne measurements still have not provided vertical height information of aerosol, quantitatively, due to the limitation of observation techniques. Recently, hyperspectral instruments onboard satellite have been launched to measure trace gas concentrations by using Differential Optical Absorption Spectrometer (DOAS) technique.
In this study, radiance spectrum in the UV and visible range was analyzed to investigate its sensitivities to the changes of aerosol optical properties and its altitude by using a radiative transfer model. Furthermore, the slant column density (SCD) of oxygen-dimer (O4) was estimated by using the O4 band located at 340, 360, 380, and 477 nm from the DOAS technique through simulated spectra. Reasonable correlation was found between the difference in O4 SCD and the aerosol effective height at the 477 nm. From the error analysis, the retrieved aerosol effective height is largely affected by its vertical distribution and SSA of aerosol, and also influenced by the AOD and surface albedo. On the other hand, the errors from the amount of atmospheric gases, instrument condition, and the variation of the cross section database for O4 are found to be negligible. Overall, the total error budget for the retrieval algorithm of aerosol effective height is estimated to be about 25% for absorbing aerosol and 55% for scattering aerosol, except the error due to the change of vertical distribution of aerosol.
The effective height of aerosol is retrieved in several cases over East Asia by using radiance spectrum from OMI. To determine the aerosol properties, aerosol type and AOD information are obtained from the aerosol type classification algorithm using visible and IR channels of MODIS. Compared with the LIDAR observation, the retrieved height tends to overestimate about 30%, which can be attributed to difference in the definition between aerosol effective height and that from LIDAR, the cloud contamination, spatial inhomogeneous of AOD, and uncertainty in aerosol optical properties.