Evaluating Satellite-Based Aerosol Retrievals Over Mountainous Regions Of The U.S.

Satellite-based aerosol retrievals from NASA’s Moderate Resolution Imaging Spectrometer (MODIS) and NASA’s Multi-angle Imaging Spectrometer (MISR) are evaluated above four mountainous U.S. sites. We (1) examine the influence of spatial and temporal variability in aerosol and surface properties on satellite / sunphotometer agreement, (2) apply and assess an automated method for optimizing collocation window and radius in the context of variability in surface properties and aerosol optical depth (AOD), and (3) compare the performance of satellite AOD products above the four sites, and examine factors influencing their performance. Maps of the Normalized Differential Vegetation Index (NDVI), topography, and land cover are used to characterize the surface properties within a 50 km radius of each site. At the eastern sites, satellite-sunphotometer mean bias is primarily influenced by topography, urban regions, and water bodies. Collocations at the western sites are complicated by heterogeneous surface types and NDVI. The collocation window optimization algorithm is insensitive to temporal window size and spatial radius for the eastern sites but is less successful at optimization for the western sites. Averages performed at the selected collocation window size indicate little seasonal influence at the eastern sites and reduced collocation frequency during winter at the western sites.