实验七ENVI 软件介绍目的：初步认识遥感数字图像处理软件ENVI ，了解 ENVI 的组成；掌握TM 、ETM+ 数据的ENVI 读取；认识ENVI 的数据文件；掌握辐射亮度和反射率的计算。实验原理：关于头文件的解读， 传感器记录的数据， 遥感的基本物理量， 辐射亮度与DN 值之间的关系。Use Landsat TM calibration to convert Landsat TM or ETM digital numbers to radiance or exoatmospheric reflectance (reflectance above the atmosphere) using published post-launch gains and offsets (see http://landsat7.usgs.gov/cpf/cpf.php and http://edcftp.cr.usgs.gov/pub/metadata/satellite/landsat7.tar.gz). The spectral radiance (Ll) is calculated using the following equation: where QCAL is the calibrated and quantized scaled radiance in units of digital numbers, LMINl is the spectral radiance at QCAL = 0, LMAXl is the spectral radiance at QCAL = QCALMAX, and QCALMAX is the range of the rescaled radiance in digital numbers. LMINl and LMAXl are derived from tables provided in the Landsat Technical Notes (August 1986) with the information provided through the TM Calibration Parameters dialog in ENVI. QCALMAX is 255 for all TM data and 127 for all MSS data except Band 4 (0.8 to 1.1 mm), which is 63 for certain time periods (data acquired before February 1, 1979 for Landsat 1-3 and processed before October 22, 1982). The resulting radiance (Ll) is in units of watts per square meter per steradian per micrometer (W/(m2*sr*mm)). The exoatmospheric reflectance (rp) is calculated using the following equation: where Ll is the spectral radiance, d is the Earth-Sun distance in astronomical units, ESUNl is the mean solar exoatmospheric irradiance, and qs is the solar zenith angle in degrees. ESUNl is derived from tables provided in the Landsat Technical Notes (August 1986). The resulting reflecta...
