Instrumental delay calibration

Instrumental / sub-band delay calibration (sub_band_delay)

This step produces the instrumental delay calibration which removes the phase jumps between spectral windows induced by antenna-related signal paths. This paves the way for multi-band fringe fitting which increases S/N for fringe-fitting on phase calibrators.

Parameters

        "sub_band_delay":{
        "select_calibrators": [["default"]], #If default, use fringe finders otherwise specify field names 
        "time_range"        : [""], #Often want to select a short 2 min time range with all antennae on source (CASA convention input)
        "sol_interval"      : ["inf"], #Solution intervale (inf = Combine all data from one scan)
        "min_snr"           : [5.0], #Minimum S/N to pass good solution (consider higher value if fringe-finder used)
        "fringe_niter"      :  300, #Number of iterations of global fringe fitting (ok to keep as 300)
        "do_disp_delays"    :  true, #Calculate dispersive delays (ok as true)
        "extensive_search"  :  false, #Currently not available
        "modify_sbd":{ #Currently not available
            "run"           :  true,
            "spw_passmark"  :  0.5,
            "clip_badtimes" :  0.66
        },       
        "hpc_options":{
            "partition"     :  "default",
            "walltime"      :  "default",
            "nodes"         :   -1,
            "cpus"          :   -1,
            "mpiprocs"      :   -1,
            "nodetype"      :  "default"
        }

Recommended use: It is advised to use a 2-5 min interval on a bright fringe finder to calculate the sub-band delays. This means that you may want to set "select_calibrators" and "time_range" to an appropriate interval (look at the listobs file - format <project_code>.listobs.txt). The "time_range" parameter should be in the CASA format (e.g., 2021/01/14/12:07:04.0~12:07:52.0).

You may want to specify multiple fields if only some antennae observe each fringe finder. In this case, we run this step with multiple instances e.g.,

"select_calibrators": [["default"],["J1011+0106"]],
        "time_range"        : ["","2021/01/14/12:07:04.0~12:07:52.0"],
        "sol_interval"      : ["60s","inf"],
        "min_snr"           : [20.0,5.0],

This will derive solutions (with a S/N > 20) every 60s for entire fringe finder scans and then derive further solutions on J1011+0106 (with a S/N > 5), within the time frame of 12:07:04 to 12:07:52, and combining all data together.

Expected inputs

• Measurement set (<project_code>.ms)

Expected outputs

• Sub-band delay calibration table (<project_code>.sbd)