An Investigation of the Remote Sensing Of Aerosols Based on MODIS Data for Western Australian Conditions
The Department of Land Information W.A. (DLI) operates a MODIS direct broadcast system producing surface reflectance in near real-time using atmospheric correction from the Simple Method for Atmospheric Correction (SMAC) code and a time-series Bidirectional Reflectance Distribution Function (BRDF) determination from the atmospherically corrected data. The SMAC code currently uses a single fixed value for Aerosol Optical Depth (AOD).
The purpose of this project is to provide accurate AOD from MODIS data for the entirety of W.A. in near real-time (NRT) for atmospheric correction.
Three methods of AOD retrieval will be investigated for accuracy and suitability for the surface conditions found in W.A.
The first two methods are used within MODIS institutional algorithms developed by NASA for global applications and are designated MOD04 and MOD09. Both algorithms use an empirical relationship based on surface reflectance in the near infrared to infer surface reflectance for blue and red wavelengths which leads to the production of AOD and aerosol properties. The third method is being developed in-house by DLI and Curtin University and is driven by a reflectance change determination based on time-series BRDF. This compares the most current SMAC code corrected observation with a predicted surface reflectance from the BRDF. The difference or change between the two reflectance values can then be attributed to a change in the atmospheric aerosol.
The AOD output from the MODIS institutional algorithms is compared to in-situ sun photometer data to ascertain the accuracy of the retrieval methods. The suitability of these algorithms for use in the NRT atmospheric correction process can be determined from an examination of the spatial coverage of the algorithm output. The reflectance change method is investigated for suitability through radiative transfer modelling and sensitivity analysis.
These results will be presented and their implication for NRT atmospheric correction will be discussed.