Sources of Satellite Data

There are three basic sources of satellite data for import into Terascan:
  1. Level 1B data tapes from the National Climatic Data Center
  2. Level 1B data files from the Satellite Active Archive
  3. Terascan Data Files from colleagues with a satellite receiving station
    The following organizations have been generous to us in the past, and we thank them!

Which source should I use?

In general, data from the National Climatic Data Center cost money, and data from the other sources (usually) is free. The NCDC has the largest archive by far, extending back to the start of the NOAA Polar Orbitor program in 1978. The SAA has data extending back to about 1993. Data from the organizations with Terascan receiving stations has been obtained through careful and thoughtful interaction with each organization, and could be jeopardized if not dealt with tactfully. The have provided data to us in the past, but they are under no obligation to do so in the future, so be polite!

GAC, LAC or HRPT...What is the Difference?

AVHRR data is available at two different spatial resolutions, 1.1 km and 4.4 km. Since this is remote sensing, we need to use acronyms, so 1.1 km data is referred to as Local Area Coverage (LAC), and 4.4 km data is referred to as Global Area Coverage (GAC). Both of these formats refer to data that was recorded on the satellites onboard tape recorders and broadcast down to one of NOAA's receiving stations. Generally speaking, LAC is only available over the continental U.S., and GAC is available globally. HRPT refers to High Resolution Picture Transmission, and is also known as direct broadcast. This is 1.1 km data that is constantly being transmitted by the satellite as it orbits. If you have a receiving antenna, you can receive this data anywhere in the world when the satellite is above the horizon. Thus, folks with receiving stations receive HRPT, and the rest of us order GAC or LAC data out of the archives.
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