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Long Term Acquisition Plan Files The Long Term Acquisition Plan (LTAP) is used to direct the acquisition by Landsat 7 of Worldwide Reference System (WRS) scenes around the world for archiving in the U.S. EROS Data Center. The contents of the following files represent the underpinnings of the LTAP:
1. The seasonality file specifies which WRS scenes are to be acquired during which periods of time (request period), and the frequency of acquisition during those periods. This file covers the year 2001 and includes both daytime and nighttime imaging. Frequency of acquisition is defined as either "once" during the request period, or "all" opportunities during the request period. The results of ingesting this file into the scheduler and developing the daily schedule are posted daily on the web, at this server location. Here is the warning label associated with the seasonality file:
The result of this juggling is that scenes marked with an "all" opportunities frequency are usually acquired every 4-5 cycles (64-80 days) instead of every cycle (16 days). Another outcome of this is that scenes marked with a "once" frequency may be acquired multiple times within the request period in an attempt to better the cloud cover results, should the first acquisition's cloud cover be considerably worse than the nominal. So please treat the frequency assignment in the seasonality as a guide, not a rule. The column headings for the seasonality file are:
2. The WRS land data base identifies those WRS scenes containing land or shallow water which will be imaged at least once every year. At the end of the file are separate tables for the niche communities and special interests. These include: EOS validation sites, glaciers, MODIS fire validation sites, political (disputed sites), volcanoes, global oceanic islands. A comprehensive reef list is a future addition. 3. and 4. The nominal cloud cover file reports the average cloud cover for each WRS scene for each month of the year. The file spans one year and addresses the descending rows only.The nominal cloud cover daylight additions file adds those ascending rows which will be in daylight during some part of the year and therefore may be imaged. The average cloud cover is derived from the International Satellite Cloud Climatology Project D2 data set, years 1989-1993. As subsequent years are processed, this file will be updated. The columns in the nominal cloud cover files are: first day of month|last day of month|path|row|cloud cover value all cloud cover values for row 1 across all paths are given, then for row 2, etc. 5. The nominal
gain settings file identifies the gain settings that will be
used as defaults for each WRS scene for each day of the year. This
file spans one year. The scheduler uses the DOY value. The DD-MMM
values that are included in the file are for a leap year and are
guidance for those who don't easily equate a DOY value of 177 with
the date 25-JUN. The file addresses both descending and ascending
rows of interest to the U.S. archive. The settings are given as
H for high gain or L for low gain. The order in which they are specified
for each scene is bands 123456678, where band 6 is repeated twice,
once for format 1 and once for format 2, and band 8 is the panchromatic
band. You will notice that bands 66 are constant at LH and band
8 is constant at L. The other bands are changed in groupings, with
bands 123 changed together, band 4 changed on its own merits, and
bands 57 changed together. When we do night imaging, we use the
following default settings: HHHHLLHLL. The file only contains
entries showing when the default gain setting has changed from its
previous setting. The default gain settings are generated using
rules that take land cover type and sun angle into account.
To understand these rules, read the file "gain
setting rules". Other files referenced by this document
are:
6. The maximum solar zenith angle is a single value for all scenes at all times of the year. Daylight imaging will not be scheduled if the angle is 85 degrees or more (same as 5 degrees or less in elevation from the earth's surface).
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