BANDPASS CORRECTIONS ACROSS SIDEBANDS

In some cases, one of the sidebands is affected by the pressure-broadened lines in the Earth atmosphere (e.g. the water and ozone lines). Users might want to try corrections for the instrumental bandpass on the data using the bandpass solutions derived from the image sideband. Miriad smagpplt has provided an option xpass to transfer the bandpass solutions from the image sideband. Assuming vis_rx1.lsb.tsys and vis_rx1.usb.tsys, the multiple source files of the lower-side-band and upper-side-band with Tsys corrections, here is a recipe for users to try the bandpass corrections across sidebands in Miriad

1. Create small vis-files with the bandpass calibrator

uvaver vis=vis_rx1.lsb.tsys select='source(3c279)'  out=340bp_lsb \
        options=nopass,nocal
uvaver vis=vis_rx1.usb.tsys select='source(3c279)'  out=340bp_usb \
        options=nopass,nocal

2. Derive bandpass solutions

smamfcal vis=340bp_lsb  \
        refant=5 interval=1000 edge=20,20 \
        select='pol(rr,ll),window(12,13,14,15)' \
        weight=2  options=msmooth,averrll smooth=5
smamfcal vis=340bp_usb  \
        refant=5 interval=1000 edge=20,20 \
        select='pol(rr,ll),window(12,13,14,15)' \
        weight=2  options=msmooth,averrll smooth=5

3. Plot bandpass solutions

smagpplt vis=340bp_lsb device=1/xs yaxis=a,p \
        options=bandpass \
        polyfit=4 nxy=2,3
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smagpplt vis=340bp_usb device=1/xs yaxis=a,p \
        options=bandpass \
        polyfit=4 nxy=2,3

4. Transfer the bandpass solutions across sidebands (lsb to usb)

smagpplt vis=340bp_lsb,340bp_usb  \
        options=xpass

5. Copy over the bandpass to the target file

gpcopy vis=340bp_usb out=vis_rx1.usb.tsys

6. Apply the bandpass

uvaver vis=vis_rx1.usb.tsys out=vis_rx1.usb.tsys.bp