Information for Visitors about Computers at GMRT

Preparing for Observations:

Source Parameters: 

Create source list in your home area in similar to the source list in /btemp2/source/vlacal.list. The spacings between the columns are important. The sample command file is in  /btemp2/cmd/sample.cmd. Once you are ready with the source list and command file, inform operators. They will check these and upload them to online machine.


Frequency Settings:  

A standard form available in the control room where the frequency settings can be filled in. Every GTAC user should fill in this form indicating the observing frequency, bandwidth, integration time and other details. Giving verbal instructions can lead to wrong settings due to language problems.

gtac1 PC has DAT72 drive, astro6 and proj3 have DDS3 drive. On a DAT72 tape about 30GB GMRT data and on a DDS3 tape 10 to 11 GB of GMRT data (GMRT raw data and/or FITS) can be written by tar command or through aips.  Default data area where the GMRT raw data is recorded is /rawdata for USB data and /rawdata1 for LSB data. In this area data will be present in the subdirectory called by day and month e.g. /rawdata/17may; /rawdata1/17may. 

During the Observations..

Some offline analysis software  are available to look at the data. For any path confusion, source /etc/bashrc for bash and /etc/csh.cshrc or /etc/cshrc for csh. Source /astro/RC for bash shell or source '/astro/RC.csh' for csh/tcsh shell. Run the software and say explain. This will give help for the software's usage.

The following programmes will be useful for any GTAC user. 

1. ltahdr : Gives info about the GMRT raw data, which is in 'lta' format. The rawdata for USB comes with an extension .lta and LSB with .ltb. Usage: ltahdr -i . Check 'ltahdr --help' for details. 

2. tax: Graphical interface to plot the data. Using this programme, one can monitor the phase and amplitude stability of the data while the observation is in progress. Type 'tax' and then type 'explain' for more details.


Converting GMRT raw data to FITS format:

The GMRT data can be converted into FITS file using two programmes, listcan and gvfits.

1. listscan : List the scan in the ltafile for converting to FITS format. Go to /DATA/; make sure there is enough space. Run listscan (eg: listscan ). This will create a file with .log extension. Open this file with your favorite editor. The parameters you might need to change are the output FITS file name, CLASSIC_NORM (normalisation by self), removing unwanted antennas or scans, giving path to the FLAG file etc.


1. gvfits : Convert GMRT (lta) data to FITS format. Run gvfits on the above log file (eg: gvfits test.log). This will take some time depending on the size of the input file.


Miscellaneous offline programmes: 

The following programmes might not come in use for GTAC users if there are no problems in the observations. 
1. xtract: Extract data from lta file in various formats. 
2. ltacomb: combines lta files. 
3. ltaclean: cleans up ltafiles with gliches in it. First one or two records can also be removed using this programme (similar to 'QUACK' in AIPS). 
4. ltasel: allows data averaging selection. 
5. relta: allows averaging in time. 
6. offstop: Stop fringe offline by providing suitable tables antenna coordinates and fixed delays. 
7. tcalibbp : Program for bandpass calibration. 

How to get into AIPS: 

To use aips on these machines, after login do following: 
gtac1% newgrp aips 
gtac1% source /usr/aips/LOGIN.CSH (for csh) or source /usr/aips/LOGIN.SH (for bash) 
gtac1% aips 

Prefer to use aips id 1010, 1020, 1030, 1040 and 1050 for  visitor1, visitor2, visitor3, visitor4 and visitor5 accounts respectively. There is /DATA partition kept for aips data purpose. Make required number of sub directories here and edit .dadevs appropriately. 

Backup of the Data:
It is the responsibility of the visitor to take backup of their data. No backup is taken for the /DATA and /analysis area and user has to take his own backup before he leaves GMRT site. All the files from the visitor account will be deleted the day following the day visitor leaves GMRT.

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