Sources of Satellite Data
There are three basic sources of satellite data for import into Terascan:
- Level 1B data tapes from the National Climatic Data Center
- Level 1B data files from the Satellite Active Archive
- 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.
This page maintained by Dave Schneider (djschnei@mtu.edu)