Characteristics Of Microwave Brightness Temperature Background And Pre-earthquake Microwave Anomaly Around Yushu Region

The study on satellite thermal infrared anomalies has a relatively long history in pre-earthquake signals detection. However, it is difficult to recognize the anomaly in cloudy conditions, because the infrared radiation from the Earth's surface cannot pass through clouds and arrive to the satellite. Contrary to thermal infrared, microwave has a strong cloud penetrability which means less weather interference and better data continuity. So microwave is proper for real-time earthquake prediction. However, few work has been done in detecting pre-earthquake anomalies with passive microwave remote sensing. Therefore based on the problems and deficiencies that exist in the present study, this thesis used brightness temperature data at 3 frequencies (6.9GHz-H,18.7 GHz-H,36.5 GHz-V) from AMSR-E data in Yushu region to analyze characteristics of microwave brightness background fields, anomalies of microwave brightness temperature before earthquakes, and the causes of the anomaly. The main results are summarized as follows:(1) Microwave brightness temperature background fields in different time scales (daily, ten-day, monthly) were established by multi-year average. The results showed that spatial and temporal characteristics of background fields in three time scales were basically the same at the same frequency. The spatial characteristic of background fields was determined by elevation, latitude, and the water distribution. The brightness temperature was negatively related to the latitude and altitude and always low in water-rich region. The temporal characteristic was mostly determined by seasons.(2)The thesis used the two-step method to extract abnormal signals of microwave radiation at three different frequencies before Ms7.0 Yushu earthquake. The results indicated that before the earthquake, a positive microwave radiation strip appeared in the southwest of the epicenter, and the microwave brightness temperature at three frequencies all appeared five-stage change characteristics during Yushu earthquake, namely diffused phase, continuous phase, weakening phase, and finally distribution along seismogenic fault. The anomaly disappeared after that five stages. Characteristics of brightness temperature change were different among different frequencies.36.5GHz-V was more sensitive to earthquake activities than 6.9GHz-H and 18.7GHz-H.(3) According to analysis results of MPDI, NDVI, soil moisture, and temperature between 2010 and multi-year average, it inferred that the microwave anomaly before Yushu earthquake was caused by temperature increase and humidity drop.This research got some qualitative and quantitative results in characteristics of microwave brightness temperature background and pre-earthquake microwave anomaly. It provided some meaningful information for earthquake monitoring and prediction.