Visibility

class ska_sdp_datamodels.visibility.Visibility(data_vars=None, coords=None, attrs=None)[source]

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_intent – Intent for the scan (an 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.

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
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_intent:         none
    execblock_id:        0
    meta:                None