Can Microwave Emissivity Show Us Global Drought Estimates?

The change in land cover and drought are currently among the largest issues affecting the world, so recognizing the environmental change and sustainable development issues are important. The purpose of this study is to determine the potential in using microwave brightness temperature and emissivity data to monitor previous land cover changes and droughts. Using microwave radiation at various frequencies from satellites sensor data such as Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E) and Special Sensor Microwave Imager (SSMI) have been collected to formulate the emissivity around the globe for the last few decades. In this study, the lower frequencies are used because at such frequencies, the signal is more sensitive to surface properties such as soil moisture and vegetation. The Emissivity Microwave Polarization Difference Index (EMPDI) and Brightness Temperature Microwave Polarization Difference Index (BTMPDI) are computed by vertical and horizontal value. The global EMPDI and BTMPDI values from 20 years of data are then placed in contrast with independent drought indicators from the Global Integrated Drought Monitoring and Prediction System (GIDMaPS) based on precipitation and soil moisture data records. Moreover, a drought severity test is performed using techniques that previously were deployed on precipitation and soil moisture data to investigate the potential of using microwave emissivity values in drought monitoring, directly. Results reveal some sensitivity to surface property changes and in some places they are not consistent with drought indicators. Microwave emissivity provides a signal that simultaneously is affected by vegetation and soil moisture condition. Therefore, regions with more stable and resistant land-cover type do not necessarily indicate any drought even though the precipitation records prove otherwise.