Validation and Trend Analysis of Satellite-Based AOD Data over Southern India

Aerosols are finely suspended solid or liquid particles in the atmosphere. Anthropogenic aerosols from industrialization and urbanization are among the prominent factors instrumental in climate change process. Aerosol optical depth (AOD) is a quantitative estimate of the amount of aerosol present in the atmosphere. The rise in concentration of aerosols in the atmosphere has affected the clear sky visibility in most of the metropolitan cities. AOD data from satellite and ground observations are the main sources in studying the effect of aerosol on spatial patterns of precipitation and temperature. The continuous AOD data are validated against ground observations. It is observed that Moderate Resolution Spectrometer is closely correlated with ground observations. The coefficient of determination is 0.58 for Pune station and 0.7 for Kanpur station. Trends in AOD have been assessed for 2 decades over Southern India using Mann-Kendall test and Innovative Trend Analysis (ITA) method. Both the tests showed a decrease in area of significant trend for the second decade when compared to the first decade. This might be because of change in mitigation policies adopted in India. It is observed that 67% and 40% of the area showed a significant positive trend in the first and second decades using Mann-Kendall test, respectively. However, 42% and 30% of the area showed a significant positive trend in the first and second decades using the ITA method. The variation in percentage of area in both the tests is attributed to the manner in which data are given as input and also on the mode of application. Hence, both the tests are useful to assess the trend in AOD data.