Aerosol Optical Depth (AOD) retrieval method using MODIS

Difficulties on the estimating of aerosol radiative forcing is due to lack of knowledge on the microphysical and aerosol optical properties and their extreme variations of spatial distribution. In understanding the dynamics of aerosols and the associated influence on global climatic conditions one of the critical parameter used is Aerosol Optical Depth (AOD). AOD acts as a good indicator due to strong correlation between small particle concentrations and light extinction coefficients. Daily AERONET Level 2 data provides AOD at 500nm however the data is very limited to a smaller scale only. To overcome this problem, MODIS data is used to provide daily AOD at 550nm data over relatively larger spatial at 10km twice a day. The aim of this study is to retrieve AOD value from MODIS satellite data and to compare and validate the AOD value using AERONET Sunphotometer. Comparison and validation of MODIS data using different instruments are required for the long term monitoring and accuracy improvement. The usual methodology for retrieval of AOD was used which is multi regression plane technique with mean and standard deviation. However, in this study some of the improvement was done by using multi regression plane technique with relative percentage error. The interpolation technique was used to derive AOD from AERONET and the statistical parameters and correlation coefficient (R²) are compared. From the result, MODIS is found to overestimate the AOD during the study period compared to AOD derived from AERONET. The correlation between extracted AOD from MODIS and AERONET using mean and standard deviation gave the R² at 0.9033 while R² for relative percentage error is 0.9422. Thus, from the comparison shows the importance of modifying the existing technique for the retrieval of AOD to reduce the error and uncertainties during the application of the parameter into radiative transfer model.