用NOAA/AVHRR探测地表反射率和NDVI的订正及误差分析

NOAA/ AVHRR反射率和标准化差值植被指数 (NDVI) 资料在气象、水文等领域都有广泛的应用。但因为地表双向反射和大气对可见光和近红外辐射的影响, 即使在地表没有变化的情况下, 卫星探测到的反射率和NDVI也有很大的变化。在除云处理和NOAA-14/AVHRR衰减校准的基础上, 利用6S模式对NOAA-14/AVHRR可见光和近红外反射率及NDVI资料进行了大气订正, 并利用Roujean和Rahman模式在大气订正后进行了双向反射订正。大气订正使可见光反射率减小3.34(反射率单位), 近红外反射率增加3.43(反射率单位), NDVI增加了0.22, 分别占各自平均值的78.2%, 15.9%, 35.5%。双向反射订正对NDVI的绝对值影响不大, 但消除了反射率和NDVI的不规则变化, 订正后能够较好地反映森林植被的物候效应。对各订正参数进行了误差分析, 结果表明订正对太阳和卫星天顶角的误差最敏感。

Corrections to NOAA/AVHRR Reflectance and NDVI and Their Error Analysis

NOAA/AVHRR reflectance and normalized difference vegetation index (NDVI) data have been widely used in meteorological and hydrological fields. Because the bi directional reflectance distribution of surface and the scatter and absorption effects of atmosphere, even though the surface keeps unchanged, the reflectance obtained by satellites can vary greatly. After cloud removing and degradation correcting processing, atmospheric corrections are carried out to NOAA/AVHRR visible and near infrared reflectance and NDVI data using the 6S model, and then bi directional reflectance corrections are carried out. The atmospheric correction makes the visible reflectanc decrease by 3.34 (reflectance unit), the near infrared reflectance increase by 3.43 (reflectance unit), and increases the NDVI increase by 0.22, equaling to 78.2 percent, 15.9 percent and 35.5 percent of their own respectively. The bi directional reflectance correction does not affect the amount of NDVI distinctively, but can remove the irregular variances of the reflectance and NDVI. After corrections, the reflectance and NDVI can reflect the phenological effect of deciduous forests (the land cover of the surface target). At last, based on the error analysis, the sensitivities of correction errors to the errors of correction parameters are given, and the results show that the solar and satellite zenith angles are the most sensitive parameters.