Analysis of global three-dimensional aerosol structure with spectral radiance matching

Abstract

A method is assessed which expands aerosol vertical profiles inferred from nadir-pointing lidars to cross-track locations next to nadir columns. This is achieved via matching of passive radiances at off-nadir locations with their counterparts that are collocated with lidar data. This spectral radiance matching (SRM) method is tested using profiles inferred from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) lidar observations and collocated Moderate Resolution Imaging Spectroradiometer (MODIS) passive imagery for the periods 10–25 April and 14–29 September 2015. CALIPSO profiles are expanded out to 100 km on both sides of the daytime ground track. Reliability of constructed profiles that are removed from the ground track by number of kilometers are tested by requiring the algorithm to reconstruct profiles using only profiles that are removed from it along track by more than the number of kilometers. When sufficient numbers of pixels and columns are available, the SRM method can correctly match ∼75 % and ∼68 % of aerosol vertical structure at distances of 30 and 100 km from the ground track, respectively. The construction algorithm is applied to the eastern coast of Asia during spring 2015. Vertical distributions of different aerosol subtypes indicate that the region was dominated by dust and polluted dust transported from the continent. It is shown that atmospheric profiles and aerosol optical depth (AOD) inferred from ground-based measurements agree with those constructed by the SRM method. For profiles, the relative errors between those measured by ground-based lidar and those constructed in the surrounding area are similar to the relative errors between the ground-based station and CALIPSO overpass at the closest distance. For AOD, the measurements from the ground-based network agree with those inferred from constructed aerosol structure better than direct observations from CALIPSO and close to those inferred from MODIS radiances.