The use of AVHRR data in operational agricultural assessment in Africa

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Abstract
The Assessment and Information Services Center (AISC) of the National Oceanic and Atmospheric Administration (NOAA), National Environmental Satellite, Data and Information Service (NESDIS) has been producing operational agricultural assessments since 1979. These activities provide drought early warning alerts and climate impact assessment to national and international agencies which require such information for disaster preparedness and agricultural assessment purposes. Data from the Advanced Very High Resolution Radiometer (AVHRR) aboard the NOAA polar‐orbiting satellite series have been used operationally in these assessment tasks since 1982. In 1985 and 1986, the use of satellite data has focused on medium resolution Global Area Coverage (GAC) data with an emphasis on the Sahel and Hom countries of Africa. In an operational context, satellite data are received from the Satellite Data Services Division of NOAA on a weekly basis from May through September. These data are processed into images over ten‐day periods in order to remove as many clouds as possible from the scene. They are further processed according to a unique color system designed to maximize their qualitative interpretability. The data are then analyzed on a weekly basis according to their normalized vegetation index (NVI) values as plotted on a spatial/temporal continuum. These satellite data, used in the context of agricultural assessment activities, are represented in two of three subsystems which are used to verify one another in the agricultural assessment process.