Characteristic Background of Microwave Brightness Temperature (MBT) and Optimal Microwave Channels for Searching Seismic MBT Anomaly in and Around the Qinghai-Tibet Plateau.

Microwave radiations from ground objects are capable of penetrating the shallow surface, vegetation, and atmosphere, but they are also contaminated by many natural factors. Microwave brightness temperature (MBT) data at different channels (frequencies and polarizations) have been used for studying seismic anomalies for decades. However, there lacks an in-depth research on how MBT responds to the natural but nonseismic (NbNS) factors, and the microwave channels used might not be optimal for earthquake study, which might bias the reliability of the retrieved MBT anomalies. In this study, the monthly mean MBT backgrounds (MMMBs) in and around the Qinghai-Tibet Plateau (QTP) were retrieved by using MBT data from the AMSR-2 sensors. The spatiotemporal characteristics of the MMMBs were carefully investigated and found to behave a significant spatiotemporal differentiation. The NbNS factors with profound influences on MMMBs were theoretically analyzed, and the sensitive microwave channels of these factors affecting MBT were revealed. Furthermore, the set of sensitive channels of different NbNS factors was used to determine reversely the optimal channels for searching weak seismic MBT anomalies in the QTP. The distribution map of the optimal channels has been then employed to explore MBT anomalies associated with ten large earthquakes (EQs) in the QTP, since 1997. The case studies demonstrated the good performances of the suggested channels and well verified their applicability. This study is of scientific meanings for understanding the MBT background in and around the QTP and has guiding significances for microwave channel selection of global seismic MBT anomaly study.