水稻遥感估产中AVHRR通道1和通道2的大气影响校正
Atmospheric Correction of Channel 1 and 2 for NOAA/AVHRR in Rice Yield Estimation
-
摘要: NOAA/AVHRR通道1和通道2的大气校正可简化为加法因子天空反照率和乘法因子透过率的计算。研究发现,传统的用黑色目标扣除法确定天空反照率值,主观性很强,而且直方图横坐标并非实际的反照率值,而是反照率分组值,因此简单地用直方图并不能真正确定黑色物体的反照率。改进方法首先计算NOAA/AVHRR数据的统计量,采用ENVI的选择感兴趣区功能,将统计计算得出的头几个值作为利用图像定义感兴趣区的阈值,然后在影像中判断其是否符合要求,来确定天空反照率值。用改进的方法对57幅NOAA/AVHRR数据进行计算,结果表明,简单的直方图法和统计计算结果加上影像判读的结果是有差异的,后者才能找到真正的像元最低点的值。然后再用能见度进行透射率订正,取得较好的结果Abstract: The visible and near infrared radiometric calibration for NOAA/AVHRR can be simplified as the calculation of the light scattering of additive component,and the atmospheric absorption of multiplicave component.Various methods to correct or remove the additive component have been developed,including the widely used dark object subtraction technique.A problem with this method is that the additive components for each spectral band are selected from their histogram respectively.This can create problems because the value selected from histogram is not the really reflectance but is the value which is the standard to divide reflectance into groups.An improved dark object subtraction technique is demonstrated that allows user to select additive component through the spectral statistical results and image displayed on the computer screen dynamically.The improved method can get the actually minimum spectral value .Examples of value differences between the old and improved methods for NOAA/AVHRR channel 1 and channel 2 were compared.Then the transmittance was calculated by visibility.At last,the visible and near infrared band of NOAA/AVHRR was corrected.