Derive a priori calibration products

Deriving a priori calibration products (apriori_cal)

This step will produce the observatory/a priori calibration, apply the observatory flags, and apply these to the data. There is currently support for Tsys, gaincurves, amplitude corrections from auto-correlations (DiFX correlated data only) and ionospheric dispersive delay calibration.

Parameters

    "apriori_cal":{
        "correlator"        :  "default", #select correlator, if default, information extracted from measurement set.
        "cal_weights"       :  true, #if true, calibrate weighting based upon relative baseline sensitivities (via Tsys) 
        "accor_options":{   #amplitude corrections from auto-correlations, only run if `correlator:DiFX` or DiFX in measurement set
            "solint"        :  "inf",  #solution interval - should be seconds/minute scales
            "smooth"        :  false,   #smooth accor corrections (set to false normally)
            "smoothtime"    : 180.0,   #smoothing timescale
            "interp"        : "linear" #how to interpolate corrections to the data
        },
        "do_observatory_flg": true, #if true, apply observatory flags generated on the `prepare_data` step
        "make_gaincurve"    : true, #generate a gaincurve (keep true)
        "tsys_options":{            #pipeline expects that the Tsys information (`SYS_CAL`) is in the measurement set and this creates the amplitude scaling table
            "interp_flags"  :  true, #interpolate over flagged entries
            "smooth"        :  true, #if true, smooth and filter Tsys table
            "outlier_SN"    : [2.5,2.0], #threshold for outliers filtering (typically keep as this)
            "jump_ident_pc" :  20, #Acceptable percentage jump in Tsys value (20% normally ok)
            "interp"        : "linear,linear" #how to interpolate
        },
        "ionex_options":{
            "run"           :  true, #run ionospheric correction (requires internet connection)
            "ionex_type"    : "final" #type of correction to download (options `final|rapid`). Only change if step fails.
        },
        "hpc_options":{
            "partition"     :  "default",
            "walltime"      :  "default",
            "nodes"         :   -1,
            "cpus"          :   -1,
            "mpiprocs"      :   -1,
            "nodetype"      :  "default"
        }

Recommended use: The default parameters shown here are normally ok for 99% of observations. Take care in checking the Tsys tables, especially if you decide to smooth and filter the tables. Consistently offset Tsys values can cause this outlier filter to filter the good values instead. In this case, it may be worth to replace the values with expected DPFUs.

Expected inputs

• Measurement set (format <project_code>.ms)
• (If prepare_data step run) - <project_code>.gc
• (If prepare_data step run) - <project_code>_casa.flags

Expected outputs

• <project_code>.ms with CORRECTED_DATA column and observatory flags applied (if "do_observatory_flg": true)
• System temperature calibration table (<project_code>.tsys)
• (If "make_gaincurve":true) - Gaincurve calibration table (<project_code>.gcal)
• (If correlator:DiFX or DiFX in measurement set correlation information) - Amplitude normalisation correction calibration table (<project_code>.accor)
• (If "ionex_options":"run":true) - Ionospheric dispersive delay calibration table (<project_code>.ionex)