In order to successfully create a Geolocation file from a Level 1A file,
corresponding attitude and ephemeris files are required (unless the Terra
embedded Onboard (TONS) Attitude/Ephemeris option is selected). These files
can be manually downloaded, though it is recommended to simply allow SeaDAS
to automatically fetch the required files via its built-in wget program.
To learn how to manually retrieve these files, please consult the
Ancillary Data Descriptions page for
specific instructions.
NOTE: Two MODIS ancillary data files
(utcpole.dat and leapsec.dat)
reside in the $SEADAS/var/modis/ directory and must be kept up-to-date.
Though l1agen_modis will automatically download them if they're over 14
days old, it is still suggested that they be updated on a weekly basis by
running the update_luts.py script
as a cron job. The utcpole.dat and leapsec.dat files are available here:
http://oceandata.sci.gsfc.nasa.gov/Ancillary/LUTs/modis/utcpole.dat
http://oceandata.sci.gsfc.nasa.gov/Ancillary/LUTs/modis/leapsec.dat
Command Mode:
Usage: geogen_modis, ifile="ifile", geofile="geofile", /verbosehttp, /enabledem, geocheck_threshold=percent, /savelog, /wait
Minimum command: geogen_modis, ifile="ifile"
Arguments/Keywords:
| ifile | Input MODIS L1A file for generating the Geolocation file. (Required) |
| geofile | Output filename for the GEO file. (Optional) |
| verbosehttp | If this flag is set, verbose wget output messages from attempted attitude/ephemeris downloads will be output to the SeaDAS xterm window. |
| enabledem | If this flag is set, terrain elevation correction will be enabled for all processing including over land and lakes. (MODIS DEM files are available in the seadas_dem_modis.tar.gz SeaDAS distribution file.) |
| geocheck_threshold | Percent of geo-populated pixels required to pass geocheck validation test. The geocheck validation test calculates the percentage of pixels that were not successfully geolocated and if this percentage is less than geocheck_threshold, the processing will assume failure and will not delete temporary processing files, including the log files. (Default=95) |
| savelog | Saves the geolocation processing LogStatus file. (The log is deleted by default if processing completes without a fatal error.) |
| wait | A keyword, if not set or a value 0 (default), the command will spawn the program as a background process and come back right away for the next SeaDAS command. Otherwise, if the keyword is set or with a value 1, the command will spawn the program as a foreground job and wait for it to complete before the next SeaDAS command can be executed. |
Interactive Mode:
Main Widget:
The main_widget can be accessed by selecting "geogen_modis" from the Process -> MODIS pull down menu in SeaDAS main menu or from the command line mode by typing: "geogen_modis".Input items:
Input MODIS L1A file The input MODIS L1A file for generating the Geolocation file. Select To display the File Selection Widget for selecting the input file. Output GEO file (optional) Optional output filename for the GEO file. Enable Verbose Auto-Download Messages Option to enable/disable verbose wget output messages from attempted attitude/ephemeris downloads (output to the SeaDAS xterm window). (Default=NO) Enable Terrain Elevation Correction Option to enable/disable terrain elevation correction for processing over land and lakes. (MODIS DEM files are available in the seadas_dem_modis.tar.gz SeaDAS distribution file.) (Default=NO) Geo-populated pixels threshold for test (%) Percent of geo-populated pixels required to pass geocheck validation test. The geocheck validation test calculates the percentage of pixels that were not successfully geolocated and if this percentage is less than geocheck_threshold, the processing will assume failure and will not delete temporary processing files, including the log files. (Default=95) Make Default buttons These buttons will save the current state of the corresponding option as a default for future SeaDAS sessions. (If SeaDAS is exited after a Make Default action has occurred, SeaDAS must be run in a NEWLY OPENED xterm for the change to take effect.) Log file The output file name for the processing log file if the user selects Submit. Run To start the geogen_modis program. Submit To start and run the geogen_modis program as a background process. Help Online help for geogen_modis program. Quit To quit this program.
