| Command | Comments |
|---|
| |
| %sdfits -scans=177:180 /home/archive/test-data/tape-0002/TREG_040922 | The first step in reducing GBT data with the gbtidl program is to convert (or "fill") the data from the raw GBT FITS files into one or more sdfits files. This step accomplishes the task. The output file will be called TREG_040922.raw.acs.fits. Additional information is available on the sdfits command |
| %gbtidl | Starts gbtidl and loads the appropriate scripts needed to reduce GBT data. |
| filein,'TREG_040922.raw.acs.fits' | This step identifies the input data set. If the data are contained all in one file, the filein command is appropriate. It is also possible to use a directory of sdfits files as the input, in which case the dirin command is used to identify the input directory. |
| list | Lists the records available in the input data set. |
| summary | Gives a summary of scans, listed by GBT scan number |
| getrec,0 | Retrieves the first record from the input data set. The data are copied into the primary data container (PDC): !g.s[0]. If the plotter Auto Update is ON (the default) then the data are automatically displayed in the plotter. In this case, the data are still not calibrated and so the spectrum shows just a bandpass shape. |
| show | If Auto Update is OFF, then this command forces the plotter to show the spectrum in the PDC. |
| header | Shows some header information |
| getps,177 | Calibrates the total power data from scans 177-178 and stores the result in the PDC. |
| show | Displays the calibrated spectrum. Again, if Auto Update is ON, this step is redundant. |
| for i=177,179,2 do begin getps,i & accum & end | Retrieves scans 177 through 180 and adds each to the accumulator, Although there are only two scans in this loop, the number of scans can be increased trivially by changing the limits in the loop. An alternative to using a simple loop is to use the stack to generate a list of scans to be averaged. See an example of how to use the stack here |
| ave | averages data in the accumulator and stores the result in the PDC. |
| bdrop, 10 | |
| edrop, 10 | Drop the first and last 10 channels from the display |
| sclear | Clears the accumulator |
| setregion | Prompt the user to specify the regions to be used for baseline fitting by clicking on the plotter. The baseline regions are stored in !g.nregion. The baseline regions can also be specified by setting !g.nregion directly. setregion can be run multiple times to overwrite previous results. |
| bshape, nfit=5 | Shows the result of a fifth order polynomial fit. !g.nfit is set to 5. |
| show | Clears the overlay |
| showregion, /off | Turns of the baseline box overlay |
| bshape, nfit=4 | Shows the result of a fourth order polynomial fit. !g.nfit is set to 4. If no order is given, the previous value of !g.nfit will be applied. |
| baseline | Subtracts the fourth order polynomial baseline from the data. The residual is stored in the PDC and displayed. |
| stats,4.75,4.76 | Provides statistics on data contained between 4.75 and 4.76 GHz |
| fitgauss | Fits a Gaussian profile to the data. The user will be prompted to enter the range to be fit as well as initial guesses for peak and width by clicking on the plotter. |