Satellite thermal infrared background field variation characteristics of the Qilian Mountains and the Capital Zone

Understanding the thermal infrared background field and its temporal-spatial evolution characteristics under the condition of no earthquake is the key to the effective extraction of infrared anomaly information related to earthquake.The brightness temperature background fields in the study areas of the Qilian Mountains and the Capital Zone were established using NOAA satellite thermal infrared remote sensing data from 2003 to 2011.At the same time,the temporal-spatial evolution characteristics of infrared brightness temperature background fields were analyzed.The results show that the background field of brightness temperature is influenced jointly by many factors,such as seasonal variation,terrain,and fault activity.Seasonal variation is the most important factor affecting infrared brightness temperature which has the obvious annual variation feature.In consideration of geographical environment difference,the characteristics of annual variation show different manners.The brightness temperature changes unstably in the region where topographical features are complicated.The relationship between the infrared brightness temperature and the elevation shows prominent negative correlation,and the brightness temperature is reduced by about 0.21 ～ 0.63℃ with the increase of 100 m in ground elevation,which is in accordance with the temperature lapse rate.The active fault belts obviously display linear belts or the boundary of the brightness temperature in the thermal infrared temperature images.Studies show the variation characteristics of the multi annual average background field which smoothes some climate change information such as atmosphere,and this field is regarded as a stable reference field of brightness temperature to detect the temperature-increase anomaly caused by fault activity and earthquake.