Subj: GBES deltaT Users guide
From: Toney Minter
Date: 96 December 9, updated 97 June 25

This document describes GBES offline utility program "deltaT" for 
producing the time corrections file for the correlator.

deltaT
======

The deltaT program reads through the GBES logs, the orbit predictions
file and the time residuals file in order to produce time corrections data 
for the space radio telescope data during correlation.  The times correction
data is output into a file which by default is located in the directory 
/s3/ftp/ovlbi/out.  The name of this file is reported after deltaT has 
finished running.

Like all GBES offline programs, deltaT also produces a short
help message if executed without arguments.  Ie:

% /s3/ovlbi/bin/deltaT

deltaT is an offline program which reads the phase residuals file and the
geometry (orbit) file and creates the deltaT fileto be used at the correlator.
deltaT: optional arguements are in [brackets]l; usage
deltaT -i [-f <MHz>] [-out <outfile>] [-sunspot <SSN> 
     [-noweather] [-noionosphere] [-gtcorr <gsec>] [-ttcorr <tsec>]
     <geometry file> <time residuals file> [<log files>] 
  where [-i]             ignore log file link status
        <outfile>       is the DeltaT file to be created
        <geometry file> is the orbit file used for tracking
        <time residuals>is the TWT data used for tracking
        <log files>     are the log files to be examined
        <MHz>           optional nominal DOWNLINK freq in MHz
        <SSN>           the sunspot number, for ionospheric correction
        [-noweather]    turns off weather corrections if specified
        [-noionosphere] turns off ionospheric corrections if specified
        <gsec>          is the correction in seconds to be added to the ground
                        time at the clock setting epoch
        <tsec>          is the correction in seconds to be added to deltaT due
                        to an error in setting the tape time at the clock
                        setting epoch
where <times> can be one or more of:
      -b[egin] <mjd> [<time>] first date and time to examine
      -e[nd]   <mjd> [<time>] last  date and time to examine
      -s[ingle] <mjd>         process a single day of files
      -t                      todays files (UTC date)
      -y                      yesterdays files (UTC date)
<times> must have the date (ie 96Oct31), but hours are optional
ie: -b 96Jun23                start at begining of day (0 hours)
ie: -e 96Jun23 13h30m15s      specify fixed end time

Options
=======
-i		This option tells deltaT to ignore all information from the 
		logs as to the status of the link with the spacecraft.  This 
		option should not be used unless under dire circumstances.

-f <MHz>        This option allows the user to set the nominal downlink 
		frequency used in the deltaT files.  Normally, the nominal
		downlink frequency is determined from the log files.  This
		option should not be used unless under dire circumstances.

-out <filename> This option allows the user to the define the output file name.
		This option is usually used for determining the quality of
		the deltaT data and for debugging.

-sunspot <SSN>  This option allows the user to specify the sunspot number.  
		The sunsopt number is used in calculating the ionospheric
		corrections since the ionospheric electron content is related
		to solar activity which is measured by the sunspot number.
		Normally the sunspot number is determined from the 
		~ovlbi/offline/scriptFiles/solarFlux.dat file and does not
		need to be entered.

-noweather      This option turns off the non-reciprocity correction due to
		the tropospheric delays.  This option should only be used
		in debugging deltaT.

-noionosphere   This option turns off the non-reciprocity correction due to
		the ionospheric delays.  This option should only be used
		in debugging deltaT.

-gtcorr <gsec>  This option is used to correct any know error in the ground
		time value for the ACQUIRE event.  This option should only
		be used if an error with the ACUIRE values is known.

-ttcorr <tsec>  This option is used to correct any know error in the tape
		time value for the ACQUIRE event.  This option should only
		be used if an error with the ACUIRE values is known.

<geometry file> This is a required value which specifies what orbit file was
		used during the tracking pass.  This value can be determined
		from the "passSummary" results.

<time residuals file>	This is a required value which contains the TWT phase
			residuals used in deriving the time corrections to be
			applied at the correlator.  This value can be 
			determined from the "passSummary" results.

<log files>	This option allows the user to specify the log files to be
		used.  Normally deltaT will figure out what log files it needs
		to use.



Standard Use
============
The usual way in which deltaT  will be used is to specify the the geometry 
(orbit predictions) file and the phase residuals file.  Note
that if the geometry file is in the directory /s3/ovlbi/in then the
directory structure can be omitted from the geometry file name.  
Similarly if the phase residuals  file is in /s3/ovlbi/out then the directory 
structure can be omitted from this file name. For example, if the phase
residuals file is  /s3/ftp/ovlbi/out/9610101212.phr and the geometry file is 
/s3/ovlbi/in/961010.bsp.orb, the the command line should be

% /s3/ovbli/bin/deltaT 961010.bsp.orb 9610101212.phr

OUTPUT
======
By default deltaT determines the output command file name.  The name is
given by YYMMDDHHMM.FITS where YYMMDDHHMM is the same as the name for
the phase residuals file. By default the output file is located in the 
directory /s3/ftp/ovlbi/out.

If deltaT has succesfully created an output file with (x) number of data points
in it then the following will be output:

Output File: /s3/ftp/ovlbi/out/9612051210.FITS.e has (x) points


Depending on what happened during the tracking pass several of these lines
could be output for a single tracking pass.  If no such lines are output
then the deltaT program did not run succesfully.

The last line output by deltaT will state wether or not the program was
run successfully.

PLATFORMS
=========
Currently deltaT will only run on machines running Solaris.