Seasonal variation in atmospheric optical depth (AOD) and thermal inertia (TI) inter-relationship over Martian Gale crater

Abstract

Investigating the relationship between thermal inertia (TI) and aerosol optical depth (AOD) is significant in giving insights into the seasonality of dust deposition and lifting phenomenon. The present study focuses on establishing a relationship of AOD with TI and different particle sizes over different Martian seasons. Two different Martian landforms (exposed rock and sand dunes) have been used to establish these relationships. TI layer was generated using THEMIS nighttime images for different seasons, whereas Curiosity Rover measured AOD values and Mars Climate database (MCD) visible column dust optical depth were used to derive rover equivalent AOD. An inverse relation was observed between AOD and TI for exposed rock and sand dune regions for all the seasons with low to moderate coefficient of determination (R²⁾. A similar inverse trend was observed between rover equivalent AOD and particle size with R² values ranging from 0.8 in the case of sand dunes (winter) to 0.93 in exposed rock (autumn). The results were further compared within the AOD obtained from orbiter image (HRSC) derived using Shadow method for spring season (Shaheen et al., 2022). The same inverse relation was found within TI having good R² values of 0.61 for exposed rock and 0.76 for the sand dunes. Error estimation using Mean Absolute Error (MAE), Root Mean Square Error (RMSE), Normalized Mean Square Error (NMSE), Fractional Bias (FB), Index of agreement errors was carried out for TI vs. AOD and particle size vs. AOD. Excellent statistical significance was obtained for AOD and particle size, in the case of sand dunes it was 0.96 for autumn and 0.99 in case of exposed rock for spring season, respectively.