Aerosol Optical Depth Model Assessment With High-Resolution Multiple Angle Sensors

The Naval Postgraduate School Aerosol Optical Depth (NPS AOD) model has been used successfully to retrieve aerosol optical depths over water using Advanced Very High Resolution Radiometer (AVHRR) imagery. In this work, the NPS AOD model is applied to the QuickBird high-resolution commercial satellite imagery collected at multiple zenith angles around Sir Bu Nuair Island, United Arab Emirates in September 2004 during the Unified Aerosol Experiment, United Arab Emirates (UAE2) Campaign. The QuickBird-retrieved aerosol optical depths are compared to other satellite and ground-based optical depth retrievals, including those from the Aeerosol Robotic NETwork (AERONET), the MODerate resolution Imaging Spectroradiometer (MODIS), Multi-angle Imaging Spectroradiometer (MISR), and AVHRR. Adapting the NPS AOD model to the nominally 2.4-meter resolution imagery from QuickBird required using modal radiances determined over an area that matched the lower resolution imagers (~ 275 meters to 1 kilometer). Additionally, the NPS AOD model was originally developed for the AVHRR imager on the NOAA-14 satellite. The NPS AOD model selects a modeled aerosol size distribution and scattering phase function based on the ratio the red and near-infrared channels of the AVHRR and the scattering angle derived from solar-sensor geometry. As such, the LUT that relates the ratio of red and near-infrared radiances was based on the center effective wavelengths of the NOAA-14 channels. The AOD retrievals from the other imagers must be adjusted to account for the changes in center effective wavelengths of the red and near-IR channels. Results show that the application of the NPS AOD model to QuickBird data yields findings that are consistent with other satellite and ground-based retrievals. In general, the NPS AOD model works well for nadir and near-nadir view angles, but not for zenith angles greater than 50 degrees. A non-linearized single scattering model and additional scattering streams will be investigated to address these shortcomings.