COMPARATIVEANALYSIS OF AEROSOL OPTICAL DEPTH (AOD) DERIVED FROM SATELLITE –BASED RETRIEVALSWITH GROUND-BASED SUN PHOTOMETER OBSERVATIONS.

Abstract

This study aims at carrying out comparative analysis of Aerosol Optical Depth (AOD) from various satellite platforms and ground observations from Aerosol Network (Aeronet) over West African Countries between January 2005 and December 2012. This study presents results from eight year observation at four West African sites and a location in the Atlantic ocean in order to investigate the spatial temporal distribution of aerosol over West African region. The station under study include Banizoumbou (130320N,020 390E), Niger (130 450N,020, 390E), Agoufou, Mali (150 210N,10,290W), Ilorin Nigeria (080 320N, 040 340E), Ouagadougou, Burkina-Faso (120 220N. 10 310W), and Cape Verde tropical Atlantic Ocean (160, 450N, 220 570W). The satellite data for this study was gotten from different platforms for a period of 8 years on monthly basis. Aerosol optical depth angstrom and size distribution were obtained from the measurement of ground based aerosol network of sun-photometer at wavelength 440nm on cloud free days. In order to compare the satellite aerosol index data with the ground based aerosol optical depth, regression analysis was done to obtain the correlation between the two parameter, for each of the stations. Results of the day-to-day A0D440nm variations as well as the seasonal and annual variations are presented in order to monitor the movement of aerosol in the region and relationship between their output data. Satellite derived data; MODIS terra and TOMS A1 data with the ground based AERONET measurement. Thus, the seasonal cycle in aerosol optical depth correspondent to the seasonal variability in dust, biomass burning and mixed aerosol emission during the harmattan dry period to the dust free rainfall season. In conclusion, there are stronger relationship between MODIS terra and ground based sun-photometer AERONET measurement with correlation coefficient R2>0.60 reported in all stations while low coefficient as low as 0.45 were obtained for regression between TOM A1 and ground based sun photometer AERONET data.