Visibility

class ska_sdp_datamodels.visibility.Visibility(data_vars: DataVars | None = None, coords: Mapping[Any, Any] | None = None, attrs: Mapping[Any, Any] | None = None)

Bases: Dataset

Visibility xarray.Dataset class

Visibility is defined to hold an observation with one direction.

The phasecentre is the direct of delay tracking i.e. n=0. If uvw are rotated then this should be updated with the new delay tracking centre.

Polarisation frame is the same for the entire data set and can be stokesI, circular, circularnp, linear, linearnp.

The configuration is stored as an attribute.

The scan information are stored as:

  • scan_id – Scan number ID

  • scan_intents – A list of intents for the scan (a scan number may have multiple intents).

    Fixed set of string for a telescope

  • execblock_id – A number that is unique to the observation execution block.

    Used to get more info from the online system of some telescopes.

“imaging_weight” provides means to store weights that are updated during processing (e.g. during imaging), while “weight” itself should not change after initialization.

Warning:

“imaging_weight” and “uvw_lambda” only exist as data_vars of the Visibility DataSet if they are explicitly set/called via the Visibility.visibility_acc object.

Here is an example:

<xarray.Visibility>
Dimensions:            (baselines: 6670, frequency: 3, polarisation: 4, time: 3, uvw_index: 3)
Coordinates:
  * time               (time) float64 5.085e+09 5.085e+09 5.085e+09
  * baselines          (baselines) MultiIndex
  - antenna1           (baselines) int64 0 0 0 0 0 0 ... 112 112 112 113 113 114
  - antenna2           (baselines) int64 0 1 2 3 4 5 ... 112 113 114 113 114 114
  * frequency          (frequency) float64 1e+08 1.05e+08 1.1e+08
  * polarisation       (polarisation) <U2 'XX' 'XY' 'YX' 'YY'
  * uvw_index          (uvw_index) <U1 'u' 'v' 'w'
Data variables:
    integration_time   (time) float32 99.72697 99.72697 99.72697
    datetime           (time) datetime64[ns] 2000-01-01T03:54:07.843184299 .....
    vis                (time, baselines, frequency, polarisation) complex128 ...
    weight             (time, baselines, frequency, polarisation) float32 0.0...
    flags              (time, baselines, frequency, polarisation) int32 0.0...
    uvw                (time, baselines, uvw_index) float64 0.0 0.0 ... 0.0 0.0
    channel_bandwidth  (frequency) float64 1e+07 1e+07 1e+07
    time_centroid     (time, baselines, frequency) float64 5.085e+09 5.085e+09.
    exposure           (time) float64 99.72697 99.72697 99.72697 ...
    (optional:)
    imaging_weight     (time, baselines, frequency, polarisation) float32 0.0...
    uvw_lambda         (time, baselines, frequency, uvw_index) float64 0.0 .....
Attributes:
    phasecentre:         <SkyCoord (ICRS): (ra, dec) in deg    (180., -35.)>
    configuration:       <xarray.Configuration>Dimensions:   (id: 115, spat...
    polarisation_frame:  linear
    source:              anonymous
    scan_id:             0
    scan_intents:        ["science"]
    execblock_id:        0
    meta:                None

Methods Summary

constructor([frequency, channel_bandwidth, ...])

Visibility

copy([deep, data, zero])

Copy Visibility

Methods Documentation

classmethod constructor(frequency=None, channel_bandwidth=None, phasecentre=None, configuration=None, uvw=None, time=None, time_centroid=None, exposure=None, vis=None, weight=None, integration_time=None, flags=None, baselines=None, polarisation_frame=<ska_sdp_datamodels.science_data_model.polarisation_model.PolarisationFrame object>, source='anonymous', scan_id=0, scan_intent='none', scan_intents=None, execblock_id=0, meta=None, low_precision='float64')

Visibility

Parameters:

  • frequency – Frequency [nchan]

  • channel_bandwidth – Channel bandwidth [nchan]

  • phasecentre – Phasecentre (SkyCoord)

  • configuration – Configuration

  • uvw – UVW coordinates (m) [:, nant, nant, 3]

  • time – Time (UTC), mid-point of the nominal sampling interval [:]

  • time_centroid – The centroid of the effective data interval [:, nant, nant, nchan]

  • exposure – The effective integration time [:]

  • baselines – List of baselines

  • flags – Flags [:, nant, nant, nchan]

  • weight – [:, nant, nant, nchan, npol]

  • integration_time – Integration time [:]

  • polarisation_frame – Polarisation_Frame e.g. Polarisation_Frame(“linear”)

  • source – Source name

  • scan_id – Scan number ID (integer)

  • scan_intent –

    Intent for the scan (string).

    Deprecated since version Use: scan_intents instead.

  • scan_intents – Intent(s) for the scan (list of strings)

  • execblock_id – Execution block ID (integer)

  • meta – Meta info

copy(deep=False, data=None, zero=False)

Copy Visibility

Parameters:

  • deep – perform deep-copy

  • data – data to use in new object; see docstring of xarray.core.dataset.Dataset.copy

  • zero – if True, set visibility data to zero in copied object