CONSTRICTOR parameters for astrometric reductions

Atmospheric dispersion corrections are based on the variation of the visibility phase with wavelength. In order to increase the SNR for these data, we coherently integrate the complex visibility for typically 200 ms. The coherent integration is done using the COBRA procedure cohstrictor. In order to provide the necessary input file for this step, the following CONSTRICTOR parameters should be used.

• OutFile = YYYY-MM-DD.coh. The .coh extension is standard for coherent integration.
• Raw = On. Write the raw data of every scan into a separate HDS file. These files are needed by cohstrictor to compute the complex visibilities and fringe delays.
• NumAv = 100. Integrate 100 2ms samples. This seems to be a good trade-off between SNR and possible systematic error at longer integration times.
• Metrology = On. Pass on metrology data