Identify Baseline-based Bandpass Errors

One might need to inspect the spectra on each baseline in the uv data set (sgrb228a_rx0.lsb.tsys.bp) after the antenna-based ripples are corrected. We pick up the strong point source 3c454.3 to identify any baseline-based errors in the bandpass:

smauvspec vis=sgrb228a_rx0.lsb.tsys.bp \
        select='source(3c454.3)' interval=1000  \
        axis=freq,both device=/xs nxy=1,1 yrange=0,40

Figs. 3.7 and 3.8 display some of the baselines which clearly show large chunk-based offsets in amplitude on some baselines (e.g. baselines 1-4 for chunk 23 and 3-4 for chunk 15.) or significant phase drift along the channels on some other baselines (e.g. baselines 2-7 and 4-7). The baseline-based errors must be removed prior to the further data reduction.

Figure: Examples of spectra after correction for bandpass ripples show the residual baseline-based errors, such as the large chunk offsets in amplitude on chunk 23 of baseline 1-4 and chunk 15 of baseline 3-4.

Figure: Examples of spectra after correction for bandpass ripples show the residual baseline-based errors, such as the large phase drift along channel on baselines 4-7 and 2-7.