The processing steps used for each individual map were:

- input a single map using corinpscan
- Do a linear fit to the cal deflections. Use this rather than the actual cal deflections. This data was taken when the cal deflection was taken at the end of the drift scan rather than the beginning (I think..). The telescope was stationary and the sky was drifting while the cal was turned on/off. If a continuum source drifted through the beam during this time, the cal deflection would be contaminated. The linear fit (throwing away outliers) would be an attempt at fixing this problem.
- scale the data to kelvins using the cal fits.
- Do the band pass correction with cormapbc(). Various methods were tried for the bandpass correction:
- do a linear fit by channel along the strip direction throwing out outliers. Use the mean value of the fit for along each channel as the bandpass value for that channel.
- compute the median by channel over the strip and use that for the bandpass correction.
- Remove Tsys (also in the routine cormapbc()). For each spectra tsys was computed by taking the median over the channels, or a robust average (throwing out outliers). This was done after the bandpass correction. The computation did not use 10% of the channels on each edge of the bandpass.
- The map was then converted to Jy use the gain curve.
- This process was then repeated for the 21 different maps.

- Top image: This a dynamic spectrum of strip 16 for a single map. The data has been bandpass corrected using the median bandpass for the strip. The horizontal stripes are coming from a continuum source (720 mJy max, about 500 mJy this strip). The upper/lower strips are the sidelobes. The vertical strip on the right is from the galaxy. (note the horizontal axis is labeled freq Mhz but it is actually channel number ...).

Bottom image: This is the sum of 21 maps of strip16. A median bandpass over each strip was used and then a robust average for each spectra removed Tsys. After conversion to Jy, the 21 maps where then added together. There is a shadow of the continuum source present. The galaxy image goes through then entire strip.

- The units are Tsys. The continuum source peaks at strip sample 67. The galaxy appears in samples 95 through 115 (bracketed by the dashed lines).

The problem is that there are not enough uncontaminated samples to compute a good bandpass correction. You could take more samples (a longer strip) or remove the continuum sources before computing the bandpass correction. This removal is a bit tricky (especially if there is absorption in the continuum source spectra).

To solve this problem mary putman suggested breaking
the strip of 120 samples up into smaller sections, computing the median
of each of these sections, and then taking the minimum value of these sections
for the bandpass correction.

The next image shows the band
pass correction breaking the strip up into 3 sections and computing
the median on each section.

- Top image. This is the same single map image with just a median bandpass as the previous image.
- Bottom image. This is the sum of 21 maps using the 3 section median as the band pass correction. The continuum has been removed similar to the first image.

processing:usr/a1552/new/pg1211/do_3.pro

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