The Impact of Aerosol Vertical Distribution on Aerosol Optical Depth Retrieval Using CALIPSO and MODIS Data

Abstract:

This study investigates the impact of aerosol vertical distribution on the retrieval of Aerosol Optical Depth (AOD) with MOderate Resolution Imaging Spectroradiometer (MODIS) Aqua data. Two kinds of vertical distribution functions were investigated in the AOD retrieval, which are exponential and Gaussian function, applied in MODIS AOD C6 algorithm and in our algorithm, respectively. The Gaussian function is with a mean height μ and the layer thickness σ with a fixed value of 0.5, where the mean height is extracted from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO).

The results show that the AOD retrieval is not sensitive to distribution functions (Gaussian and exponential function) used, but sensitive to the aerosol layer mean height. Small difference (< 1%) was found in the AOD retrieval when different distribution function (exponential or Gaussian function) used. The difference in the AOD retrieval caused by the aerosol layer mean height can be up to 13%, and this becomes more obvious under a relatively heavy aerosol loading (AOD > 1.0).

It suggests that a fixed function (specifically a fixed mean height) is not suitable for the AOD retrieval with MODIS data under > 1.0. The mean height of aerosol layer derived from CALIPSO is expected to be taken into account for MODIS AOD retrieval in the near future.