TRMM Overflight Finder

TRMM Overflight Finder icon

 

The TRMM Overflight Finder (TOFF) web page is permanently down.   A Linux command line version of the tool is available to download and install from the PPS FTP site:

ftp://gpmweb2.pps.eosdis.nasa.gov/pub/TOFF/

 

TRMM has run out of fuel so NASA is no longer performing station keeping maneuvers.  TRMM's final station keeping maneuver was July 8, 2014, so it's orbit altitude has been decreasing steadily since then.  Maneuvers were routinely performed every 15 to 20 days to keep TRMM's altitude near the optimal 402 km.

The accuracy of the command line TRMM over flight finder depends upon the TRMM orbit altitude being approximately 402 km.  With TRMM now losing altitude, that accuracy is degrading quickly.

PPS is currently developing a public subscription service where the user will choose any of TRMM, GPM, or the partner satellites, input a ground site, and PPS will generate an overflight file for the user.  ETA for that service is most likely the end of 2014.  Users will need to complete a simple registration process with PPS.

 

The Linux command line version of the tool takes the same inputs as the web page version: start date, end date, latitude and longitude of the location on the Earth, and radius from the location on the Earth. The user will have to perform minor set up, build two libraries, and then build the overflight finder executable. All code is in C. The user will need to be on a Linux computer, have a C compiler, and will need to work in a C-shell (csh) or TC-shell (tcsh).

If you download this tool, please let the PPS Helpdesk know at: helpdesk@mail.pps.eosdis.nasa.gov so PPS can alert you when new versions of input files needed by the tool are available. Three input files (listed below *) are updated routinely.

From the FTP site, please download all five files posted there:

  • README (instruction manual)
  • TOFF_YYMMDD_TAR.dat.gz (TOFF toolkit code)
  • leapsec.dat (input data file for time conversion toolkit) *
  • long.dat.gz (input data file for definitive overflight calculation) *
  • pred_fit.dat (input data file for predictive overflight calculation) *

 

See the README file for further instructions on how to setup, compile, and execute the TOFF.

If you have questions about the TOFF, contact the PPS Helpdesk at helpdesk@mail.pps.eosdis.nasa.gov.

 

 

Notes on accuracy and overflight patterns: For past overflights, accuracy is generally better than 20 kilometers in cross track position and within about a minute in time. However future overflight predictions will be less accurate, as described in our detailed overflight prediction accuracy discussion, which includes plots showing the latest trends and the date when historical data has been most recently updated. Some discussion of the patterns for the times of day of overflights is available to explain why the local times of overflight roughly change with a 46 day cycle. Also available is some discussion of how to find TRMM Overflights coincident with TERRA (EOS A.M.) or any other sun synchronous satellites.

 

Notes on mission status and operational background: TRMM operations are now expected to be maintained at least through the spring of 2005 as noted in a Jan. 4, 2005 NASA press release. The TRMM orbit was boosted in August 2001 from its initial 350 kilometer operating altitude to a 402.5 kilometer operating altitude. (Note this is a mean altitude defined from the orbit parameters while the average TRMM altitude above sea level is a couple kilometers lower, and the actual geodetic height above sea level varies over +/- 5 kilometers mainly due to the Earth's ellipsoidal shape which is flattened at the poles.) With the August 2001 orbit boost, the average instrument swath sizes increased by about 15 percent. The orbit maintenance at the 402.5 kilometer altitude was suspended temporarily in July 2005, but t reinstated thenhrough the hurricane season while the benefits of TRMM were reviewed in an interim National Academies report released in January 2005.

 

This page was developed by the Precipitation Processing System (PPS) and is maintained by Michael Hensley, Wyle Laboratories, Inc.