A Study On The Brightness Temperature Background Field Foundation And The Method For Extracting Anomalies Of Thermal Infrared In Seismotectonic Area

The seismic activities in China the has the characters of wide distribution,high frequency,big strength,shallow quakes,heavy disasters. China is one of the countries hit most seriously by earthquake in the world. Therefore ,accurate earthquake prediction,especially short-term and impending prediction is the important prerequisite of reducing earthquake disaster. The near-surface temperature anomalies prior to earthquake have been concerned by the scholars at home and abroad,who have worked a lot in this field. The research shows thermal infrared remote sensing which is used to detect infrared radiation anomalies caused by tectonic activities or seismic activities,has the widest application in the earthquake research field.On the part of extracting thermal infrared anomalies,many researchers extract infrared anomalies before earthquakes by increased brightness temperature. The satellite infrared brightness temperature is calculated according to the black body radiation law using the object thermal radiation intensity data collected and recorded by on-board sensors from surface or low altitude atmosphere. But infrared brightness temperature is the comprehensive reflection of thermal radiation of surface and atmosphere. The distribution of brightness temperature is uneven in normal situation because it is influenced by non-structural factors such as topography and geomorphology ,geophysics cover type,meteorological factor,and so on. It is unreasonable to determine whether anomalies exist or not according to the level of the brightness temperature on remote sensing images. Anomalies judgment and extraction must be on the base of understanding of the normal dynamic background. Therefore it is necessary to study the brightness temperature time-space evolution rules in normal situations,that is the premise of anomalies judgment.This paper establishes the brightness temperature background field using NOAA/AVHRR polar orbit meteorological satellite thermal infrared remote sense data in different time scales and analyses the time-space evolution features and rules of infrared brightness temperature background field at the same time,which is aimed at laying the foundations for mining thermal infrared anomalies information related to earthquake effectively. According to NOAA/AVHRR satellite data,the paper designs two brightness temperature anomalies detection and extraction on the basis of analyzing brightness temperature background field:one is brightness temperature offset index based on the same calendar year,the other is improved RST method. Moreover,we confirm the availability of extracting anomalies information using brightness temperature through the analysis of the correlation and difference between satellite observation data and field observation data.The findings indicate:(1)With respect to the foundation of infrared brightness temperature background field,the variation of brightness temperature is mainly controlled by landform and faults in space;the variation that shows the obvious characteristics of peaking in summer and low in winter is influenced by seasonal rules in time. The maximum temperature of study zone in summer is 10℃,the minimum temperature of study zone in winter is -18℃. Different geological tectonic units,especially linear active faults and water system display clearly on the thermal infrared brightness temperature images. On the whole,thermal infrared brightness temperature background field has the characteristics of spatial correlation,temporal continuity and annual variation period. We can effectively extract infrared brightness temperature anomalies based on statistic analysis of years of accumulation data;(2)The algorithm models of anomalies extraction:we design the brightness temperature offset index K based on same calendar year and improve RST,which provide technical support for the anomalies extraction;(3)Through infrared brightness temperature reality testing it can be perceived that brightness temperature shows good correlations with the air temperature and geothermal temperature in the depth of 0.2m , they have the synchronous variation tendency. This suggests that it is reliable to study earthquake anomalies using brightness temperature which is the good response of surface radiation conditions. The brightness temperature can provide the basis service for earthquake forecast.(4)At the aspect of infrared brightness temperature anomalies,the paper concludes time-space evolution rules of anomalies through studying seismic cases:the time of anomalies emergence is from days to months in time;the manifestations of anomalies is the process of weak-strong-weak-disappear,the morphology of anomalies is most cloddy or stripped which is consistent with the fault.(5)The contrast of the algorithm models of anomalies extraction:We study the earthquake of Yushu using the K-value and improved RST. The results show improved RST has the characters of sensitive reaction on anomalies,distinct details and the bigger area of anomalies,moreover,it has the advantage of deducting the temperature mutations which is caused by meteorological factors,and so on.