Calibration products

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Calibration products

By default, after processing a calibration scan, MRTCAL will save the calibration products in the CLASS output file3. They will thus be available to the user when he opens the CLASS file for reading. For example, after calibrating iram30m-4mhz-20100930s200-imb.fits and iram30m-4mhz-20100930s201-imb.fits one can see:

    MRTCAL> file in 09054.30m
    I-CONVERT,  File is  [Native]
    I-INPUT,  09054.30m successfully opened
    MRTCAL> find
    I-FIND,  14 observations found
    MRTCAL> list
    Current index contains:
     N;V Source       Line         Telescope      Lambda     Beta Sys  Sca Sub
     1;1 CALSKY       NULL         30ME0HLI-4M1   -600.0     +0.0 Eq   200 1
     2;1 CALSKY       NULL         30ME0VLI-4M2   -600.0     +0.0 Eq   200 1
     3;1 CONTROLD     NULL         30ME0HLI-4M1     +0.0     +0.0 Eq   201 2
     4;1 CONTROLD     NULL         30ME0VLI-4M2     +0.0     +0.0 Eq   201 2
     5;1 CONTROLD     NULL         30ME0HLI-4M1     +0.0     +0.0 Eq   201 4
     6;1 CONTROLD     NULL         30ME0VLI-4M2     +0.0     +0.0 Eq   201 4
     7;1 CONTROLD     NULL         30ME0HLI-4M1     +0.0     +0.0 Eq   201 6
     8;1 CONTROLD     NULL         30ME0VLI-4M2     +0.0     +0.0 Eq   201 6
     9;1 CONTROLD     NULL         30ME0HLI-4M1     +0.0     +0.0 Eq   201 8
    10;1 CONTROLD     NULL         30ME0VLI-4M2     +0.0     +0.0 Eq   201 8
    11;1 CONTROLD     NULL         30ME0HLI-4M1     +0.0     +0.0 Eq   201 10
    12;1 CONTROLD     NULL         30ME0VLI-4M2     +0.0     +0.0 Eq   201 10
    13;1 CONTROLD     NULL         30ME0HLI-4M1     +0.0     +0.0 Eq   201 12
    14;1 CONTROLD     NULL         30ME0VLI-4M2     +0.0     +0.0 Eq   201 12

The calibration products are saved as CLASS spectra with source name CALSKY. There are as many of them as frontend-backend combination (telescope name in CLASS). In order to find only the science data, user has to find explicitly his source name, e.g.:

    MRTCAL> find /source controld
    I-FIND,  12 observations found

A CALSKY entry is a spectrum providing the CalSky load as the main data (RY), plus a collection of Associated Arrays:

    MRTCAL> find /source calsky
    I-FIND,  2 observations found
    MRTCAL> get first
    I-GET,  Observation 1; Vers 1 Scan 200
    MRTCAL> dump
    [...]
     ASSOCIATED ARRAYS -----------------------------------------
      Number of associated arrays: 7
      Associated array #1: CALAMBIENT
        Unit:               Format: -11  Bad:   -1000.000  Dimensions: 1006 x 0
        Data:    10158.63       9447.842       ...      17594.74       15591.32
      Associated array #2: CALCOLD
        Unit:               Format: -11  Bad:   -1000.000  Dimensions: 1006 x 0
        Data:    5958.474       5238.263       ...      7394.842       7605.105
      Associated array #3: TREC
        Unit:               Format: -11  Bad:   -1000.000  Dimensions: 1006 x 0
        Data:    304.3947       304.3947       ...      177.7052       177.7052
      Associated array #4: TCAL
        Unit:               Format: -11  Bad:   -1000.000  Dimensions: 1006 x 0
        Data:    243.2139       243.2139       ...      249.4267       249.4267
      Associated array #5: TSYS
        Unit:               Format: -11  Bad:   -1000.000  Dimensions: 1006 x 0
        Data:    424.9489       423.0339       ...      279.2844       283.7039
      Associated array #6: TAUZEN
        Unit:               Format: -11  Bad:   -1000.000  Dimensions: 1006 x 0
        Data:   6.2096495E-02  6.2096495E-02   ...     5.5034418E-02  5.5034418E-02
      Associated array #7: FLAG
        Unit:               Format: -11  Bad:   -1000.000  Dimensions: 1006 x 0
        Data:    0.000000       0.000000       ...      0.000000       0.000000

Those 8 arrays provide useful information as a function of frequency:

- CalSky, CalAmbient, CalCold: the calibration loads,
- Trec, Tcal, Tsys: the receiver, calibration, and system temperatures,
- TauZen: the zenithal opacity,
- Flag: a flag array indicating if the data is reliable (0) or not (1). As of today, MRTCAL flags all the channels of a chunk if any error occurs when performing the chopper calibration (e.g. sky greater than hot load).

The Figure 1 shows an example of these arrays.

Figure 1: Calibration products as found after calibrating the file iram30m-4mhz-20100930s200-imb.fits. The default calibration bandwidth was used (20 MHz).