Dual-Polarization Responses of Microwave Radiation of Diorite in Process of Uniaxial Loading

The experimental detection of the changes in microwave radiation of rocks under pressure is key to identifying earthquake anomalies through satellite passive microwave remote sensing. However, such changes have not been comprehensively characterized due to the considerable differences in crustal lithology, weak microwave radiation signals, and strong environmental noise. Considering the intrinsic and significant diversity of different polarized microwave radiations of any materials, this study investigated the responses of different polarized microwave radiations during loading the rock materials. Thus, a synchronized detection system including multiple sensors was constructed at outdoor to reveal the stress-induced changes in C-band microwave brightness temperature (MBT) of diorite specimen. Experimental results show that both the horizontal and vertical MBT varied regularly with the changes of pressure; however, the trends of changes of MBT were greatly influenced by the polarization modes. Specifically, a positive correlation was illustrated between the change in vertical polarization MBT and cyclically varied pressure, during which the MBT changed with a rate of 0.033 K/MPa about. In contrast, the changes in horizontal polarization MBT exhibited a negative correlation with the varied pressure, and the MBT change rate was approximately -0.031 K/MPa. Based on the radiative transfer theory, it was found that the opposite MBT changes with respect to h- and v-polarizations are supposed to be caused by the dielectric anisotropy under uniaxial compression conditions. This study illustrates the significant and discernible MBT changes of diorite induced by the stress, which is helpful to identify the detectable microwave radiation anomalies before large earthquake occurrence.