gpscope-DT UPS 855

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sh_gamit is an automated gamit calculation script supplied by the MIT team, this tool is currently little used by the gamit community in France. The reason for this underuse is probably linked to the large number of options offered. This multiplicity of choice can scare off those who have already spent time trying to understand gamit and writing their own automated script.
This section presents two examples in the hope of convincing the reader that sh_gamit can simplify things.

When using this script, the active folder from which sh_gamit will be launched (known as the experiment folder), must contain a ./rinex sub-folder containing the data to be treated, and a ./tables sub-folder containing the configuration files. There are no other pre-requisites.

réseaux GPS permanents

The flow of data from permanent GPS sites is such that I launch the calculation for each day’s data separately. This is done using a “meta-script†which takes care of launching as many sh_gamit as necessary. The command I use looks like this :

-expt 4-character experiment name, found in the file names produced by gamit.
-d the calculation date chosen
-yrext adds the year as well as the day to the name of the sub-folder which will be created. This addition avoids overwriting the calculations for one year by those of the following year....
-h compression in Hatanaka format at the end of the calculation (for those who have problems with free disk space).
-orbit indicates the type of orbit used

Below, I list some of the options I use, these are often chosen for compatibility with how our computing network is organised :
-dir /data4/gpscope/cori full path to the working folder (folder changes can sometimes cause problems if the structure uses symbolic links)
-rdir /data4/gpscope/cori/rinex full path to the folder containing rinex files (for the same reason as above)
-rinex_ftpsites ign kreiz here at the LAREG and at Geosciences Azur, this option indicates where to look for the external RINEX data (by default at SOPAC and the CDDIS).
-ftp_prog wget getting remote files is performed by wget rather than ftp (only way for us to get through the IPGP gateway)

campagnes GPS

The calculation can be performed using a single command line without requiring an internet connection :

-expt 4-character experiment name, found in the file names produced by gamit.
-s calculation period
-orbit indicates the type of orbit used
-noftp prevents the external search for missing files.

I would also recommend the following option :
-yrext this option allows all the measurement campaigns to be calculated in the same experiment folder using the same parameters. This option will also facilitate subsequent work with globk/glorg in the ./gsoln sub-folder.

An internet connection may not be initially available, but at some time it must be possible to get remote files. This can be done using a single command line from the relevant manually-created sub-folder :
in ./brdc :
sh_get_nav -archive sopac -yr 1997 -doy 272 -ndays 13
in ./igs :
sh_get_orbits -archive sopac -yr 1997 -doy 272 -ndays 13
in ./rinex :
sh_get_rinex -archive sopac -yr 1997 -doy 272 -ndays 13 -sites ankr graz mate

As always, on-line help appears whenever a command is sent without any parameters.

configuration files

All of these files are generally found in the ./tables sub-folder along with many other files which the user never modifies. To clarify things, I have got into the habit of creating a ./tables.templates sub-folder which only contains the files to be modified. I will now describe this folder structure.

• gamit files :
  • autcln.cmd : “cryptic†configuration file for cleaning data on a site-by-site basis ; the less it is modified the better... [1]
  • lfile.apr.cori:file of a priori coordinates which is used at the start of the gamit calculations. CThis file is modified by gamit ! Because of this, it is fine to enter only your own sites, sh_gamit looks after combining them with the itrf file [2].
  • sestbl. : THE calculation configuration file
  • sittbl. : the site constraints file. It is simplest to copy the one describing the IGS stations and to add the following line at its beginning : SITE FIX WFILE --COORD.CONSTR.-- --EPOCH-- CUTOFF APHS CLK KLOCK CLKFT DZEN WZEN DMAP WMAP ---MET. VALUE---- NZEN ZCNSTR ZENVAR ZENTAU << DEFAULT >> ALL NNN NONE 100.0 100.0 100.0 001- * 15.0 AZEL NNN 3 SAAS SAAS NMFH NMFW 1013.25 20.0 50.0 7 0.500 0.0100 100.0

    which will leave our stations free from constraints.

  • station.info.cori : gamit equivalent to the field log describing the measurements. The file we are constantly improving. When we have finished with this file, the calculations are completed (or almost). This file is modified by sh_gamit ! I simply add my stations to this file and then I combine it with the gamit file (see below).

• fichiers sh_gamit :
  • ftp_info : file describing how external data can be accessed. The one supplied with gamit can be used when direct internet access is available. In cases such as at IPGP where a gateway filters transfers, modification of this file is the most complex and time-consuming part of the process [3]
  • process.defaults : describes the “computer†configuration of the calculation. Can be used as supplied with gamit in a first instance.
  • sites.defaults : lists all sites to be considered in the calculation and what should be done with them. Numerous instructions relate to sh_glred rather than sh_gamit. The only options that we need to worry about are :
    • localrxthe rinex file must be looked for locally (possibly in the archive mentioned in process.defaults)
    • ftprnx the file will be retrieved from external sites (blocked by the -noftp option in sh_gamit if used)
    • xstinfo prevents the automatic updating of station.info based on the header data in the RINEX file. Should always be used[Whatever is indicated in this file, sh_gamit will treat every site for which the data corresponding to the day of calculation are present in ./rinex and, if the site is not mentioned in sites.defaults, will modify the station.info to include it.]]

When all these files are ready in the ./tables.templates sub-folder, I “populate†the ./tables sub-folder :

I have kept the original format of my station.info.cori as the lines are shorter and I find the visual result easier to read (despite the “code names†for the various elements) than the never-ending lines of the new format which are generally wrapped by the word processing programme. This does not prevent mstinf2 from combining two different format station.info files into one new format file. Watch out for errors that cause the creation of an empty station.info file (the SOPAC, regularly updated, tends to generate the most errors for me) !