地表温度和地表辐射温度差值分析

依据实验数据，研究利用标准黑体源对红外辐射计测定值进行标定的方法；分析天空比辐射率的变化特性；计算天空环境辐射，与长波辐射计测定值进行比较；推算考虑天空环境辐射和地表比辐射率后的地表温度，研究地表温度与地表辐射温度的差值。结果表明：①地表辐射温度未经标准黑体源标定与标定后的差值绝对值在0.1～1℃之间；②天空比辐射率的变化范围为0.75～0.85，不同下垫面天空比辐射率日变化趋势非常一致；③用空气温湿度计算的天空环境辐射与长波辐射计测定值的差值较小，相对误差平均为3.1%，但是天空37°热红外辐射计观测值与长波辐射计测定值差值较大，相对误差平均值达到38.1%；④地表温度高于地表辐射温度，差值在0.2～1.5℃之间。

A STUDY OF THE DIFFERENCE BETWEEN TRUE SURFACE TEMPERATURE AND RADIOMETRIC SURFACE TEMPERATURE

The measurements of air temperature and air humidity were utilized to analyze the diurnal variation of atmospheric emissivity over heterogeneous surfaces and to calculate downward atmospheric longwave irradiance, from June 5th to July 6th, 2004, in Xiaotangshan area, Beijing. Moreover, sky radiometric temperature at 37 and land surface radiometric temperature with thermal infrared thermometers were employed to study the differences between surface radiometric temperature over heterogeneous surfaces without being calibrated and calibrated with standard blackbody source and the differences between surface “true” temperature, which were calculated with the downward longwave irradiance and surface emissivity, and surface radiometric temperature, which were calibrated by standard blackbody source. The results may be served as scientific reference to invert land surface temperature with remote sensing and to study land surface energy balance. The results indicated: (1) the differences of surface radiometric temperature between without being calibrated and being calibrated by standard blackbody sources ranged from 0.1 to 1℃;（2）the diurnal variation range of atmospheric emissivity ranged from 0.75 to 0.85; (3) the differences of downward atmospheric longwave irradiance between being calculated by air temperature and air humidity and being measured by pyranometer were small with the average mean error being 3.1%, while those of downward atmospheric longwave irradiance between being calculated by sky radiometric temperature at 37° with thermal infrared thermometer and being measured by pyranometer were larger, with the average mean error being 38.1%; (4) the differences between surface true temperature and surface radiometric temperature calibrated with standard blackbody ranged from 0.2℃ to 1.5℃ over various surfaces under variable sky conditions, and the higher surface radiometric temperature was, the larger the differences were. Therefore, the differences had the diurnal variation rule.