The Advanced Very High Resolution Radiometer (AVHRR) is a cross-track scanning system with a resolution of 1.1 km, with a frequency of scan twice per day (0230 and 1430 local solar time). AVHRR data used in the OTTER Project come from the instrument aboard the NOAA-11 satellite. The AVHRR Global Area Coverage (GAC) is full resolution image data that is processed onboard the satellite taking only one line out of every three and averaging every four of five adjacent samples along the scan line. The AVHRR has two high resolution modes, HRPT (High Resolution Picture Transmission) and Lac (Local Area Coverage). A HRPT data set is a real-time downlink of data while a LAC data set is recorded onboard for later playback. The OTTER AVHRR scenes are of the LAC variety.
The AVHRR has five spectral channels. Applications for channel 1 (0.58 to 0.68 micrometer) include daytime cloud and surface mapping. For channel 2 (0.75 to 1.1 micrometers) surface water delineation can be determined. Formulation of a vegetation gradient model can be created when a normalized difference vegetation index (NDVI) is taken using both channels 1 and 2. This procedure is a useful tool for global vegetation stratification and monitoring. Applications for channels 3 (3.55 to 3.93 micrometers), 4 and 5 (10.5 to 12.5 micrometers) include sea surface temperature monitoring and day/nighttime cloud mapping, snow and ice extent, ice or snow melt inception, and temperatures of radiating surfaces.
OTTER Use of AVHRR:
Analysis of the AVHRR data determined whether or not phenology of coniferous
forests is a direct function of heat and moisture. This has been proven for
other biome types. Measurements were also used to compute seasonal NDVI and
APAR.