Greenness of the Conterminous U.S.
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What is the Advanced Very High Resolution Radiometer?
The Advanced Very High Resolution Radiometer (AVHRR) is an optical multispectral scanner flown aboard National Oceanic and Atmospheric Administration (NOAA) orbiting satellites. The instrument measures reflected sunlight and emitted radiation (heat) from Earth in the visible (Channel 1), near-infrared (Channel 2), and thermal infrared (Channels 3, 4, and 5) regions of the electromagnetic spectrum. The spectral channels, resolution, and primary uses of AVHRR spectral data are given in Table 1. The temporal coverage of AVHRR sensors and information about the satellites (launch and service dates) are given in Table 2.
The image maps of Wyoming are produced from AVHRR data know as Local Area Coverage that are recorded onboard the satellite for subsequent transmission to a NOAA receiving station on Earth. These data have a resolution of 1 kilometer (km), which means that each image pixel represents a 1x1-km square on the ground. Before these data can be made into the image maps shown here a considerable amount of image processing must be done. Digital processing includes radiometric calibration, atmospheric correction, computation of NDVI values, geometric registration to the Lambert Azimuthal Equal Area map projection, and image map compositing. The results are the weekly 1-km AVHRR multispectral data sets and NDVI image maps of the conterminous United States; a portion of which are shown here. These steps are essential in the production and archiving of AVHRR data sets and images, and are particularly beneficial when these data are used for Geographic Information System (GIS) mapping and analysis. For more information see the section entitled Information Links.