These are the standard attributes of UVData objects.
Under the hood they are actually properties based on UVParameter objects.
Angle type attributes also have convenience properties named the same thing with ‘_degrees’ appended through which you can get or set the value in degrees.
Similarly location type attributes (which are given in topocentric xyz coordinates) have convenience properties named the same thing with ‘_lat_lon_alt’ and ‘_lat_lon_alt_degrees’ appended through which you can get or set the values using latitude, longitude and altitude values in radians or degrees and meters.
These parameters are required to have a sensible UVData object and are required for most kinds of uv data files.
Number of antennas with data present (i.e. number of unique entries in ant_1_array and ant_2_array). May be smaller than the number of antennas in the array
Number of antennas in the array. May be larger than the number of antennas with data
Number of baselines
Number of baseline-times (i.e. number of spectra). Not necessarily equal to Nbls * Ntimes
Number of frequency channels
Number of polarizations
Number of spectral windows (ie non-contiguous spectral chunks). More than one spectral window is not currently supported.
Number of times
Array of first antenna indices, shape (Nblts), type = int, 0 indexed
Array of second antenna indices, shape (Nblts), type = int, 0 indexed
List of antenna names, shape (Nants_telescope), with numbers given by antenna_numbers (which can be matched to ant_1_array and ant_2_array). There must be one entry here for each unique entry in ant_1_array and ant_2_array, but there may be extras as well.
List of integer antenna numbers corresponding to antenna_names, shape (Nants_telescope). There must be one entry here for each unique entry in ant_1_array and ant_2_array, but there may be extras as well.
Array giving coordinates of antennas relative to telescope_location (ITRF frame), shape (Nants_telescope, 3), units meters. See the tutorial page in the documentation for an example of how to convert this to topocentric frame.
Array of baseline numbers, shape (Nblts), type = int; baseline = 2048 * (ant1+1) + (ant2+1) + 2^16
Width of frequency channels (Hz). If flex_spw = False, then it is a single value of type = float, otherwise it is an array of shape (Nfreqs), type = float.
Option to construct a “flexible spectral window”, which storesall spectral channels across the frequency axis of data_array. Allows for spectral windows of variable sizes, and channels of varying widths.
Array of frequencies, center of the channel, shape (1, Nfreqs), units Hz
String of history, units English
Receiver or backend. Sometimes identical to telescope_name
Length of the integration in seconds, shape (Nblts). The product of the integration_time and the nsample_array value for a visibility reflects the total amount of time that went into the visibility. Best practice is for the integration_time to reflect the length of time a visibility was integrated over (so it should vary in the case of baseline-dependent averaging and be a way to do selections for differently integrated baselines).Note that many files do not follow this convention, but it is safe to assume that the product of the integration_time and the nsample_array is the total amount of time included in a visibility.
Array of lsts, center of integration, shape (Nblts), units radians
Source or field observed (string)
String indicating phasing type. Allowed values are “drift”, “phased” and “unknown”
Array of polarization integers, shape (Npols). AIPS Memo 117 says: pseudo-stokes 1:4 (pI, pQ, pU, pV); circular -1:-4 (RR, LL, RL, LR); linear -5:-8 (XX, YY, XY, YX). NOTE: AIPS Memo 117 actually calls the pseudo-Stokes polarizations “Stokes”, but this is inaccurate as visibilities cannot be in true Stokes polarizations for physical antennas. We adopt the term pseudo-Stokes to refer to linear combinations of instrumental visibility polarizations (e.g. pI = xx + yy).
Array of spectral window numbers, shape (Nspws)
Telescope location: xyz in ITRF (earth-centered frame). Can also be accessed using telescope_location_lat_lon_alt or telescope_location_lat_lon_alt_degrees properties
Name of telescope (string)
Array of times, center of integration, shape (Nblts), units Julian Date
Projected baseline vectors relative to phase center, shape (Nblts, 3), units meters. Convention is: uvw = xyz(ant2) - xyz(ant1).Note that this is the Miriad convention but it is different from the AIPS/FITS convention (where uvw = xyz(ant1) - xyz(ant2)).
Visibility units, options are: “uncalib”, “Jy” or “K str”
These parameters are defined by one or more file standard but are not always required. Some of them are required depending on the phase_type (as noted below).
Array of antenna diameters in meters. Used by CASA to construct a default beam if no beam is supplied.
Ordering of the data array along the blt axis. A tuple with the major and minor order (minor order is omitted if order is “bda”). The allowed values are: time ,baseline ,ant1 ,ant2 ,bda
Array of the visibility data, shape: (Nblts, 1, Nfreqs, Npols), type = complex float, in units of self.vis_units
DUT1 (google it) AIPS 117 calls it UT1UTC
Earth’s rotation rate in degrees per day
Per-antenna and per-frequency equalization coefficients
Convention for how to remove eq_coeffs from data
Any user supplied extra keywords, type=dict. Keys should be 8 character or less strings if writing to uvfits or miriad files. Use the special key “comment” for long multi-line string comments.
Boolean flag, True is flagged, same shape as data_array.
Required if flex_spw = True. Maps individual channels along the frequency axis to individual spectral windows, as listed in the spw_array (zero-indexed). Shape (Nfreqs), type = int.
Greenwich sidereal time at midnight on reference date
Number of data points averaged into each data element, NOT required to be an integer, type = float, same shape as data_array.The product of the integration_time and the nsample_array value for a visibility reflects the total amount of time that went into the visibility. Best practice is for the nsample_array to be used to track flagging within an integration_time (leading to a decrease of the nsample array value below 1) and LST averaging (leading to an increase in the nsample array value). So datasets that have not been LST averaged should have nsample array values less than or equal to 1.Note that many files do not follow this convention, but it is safe to assume that the product of the integration_time and the nsample_array is the total amount of time included in a visibility.
Required if phase_type = “phased”. Declination of phase center (see uvw_array), units radians. Can also be accessed using phase_center_dec_degrees.
Required if phase_type = “phased”. Epoch year of the phase applied to the data (eg 2000.)
Only relevant if phase_type = “phased”. Specifies the frame the data and uvw_array are phased to. Options are “gcrs” and “icrs”, default is “icrs”
Required if phase_type = ‘phased’. Right ascension of phase center (see uvw_array), units radians. Can also be accessed using phase_center_ra_degrees.
Date for which the GST0 or whatever… applies
We only support UTC
FHD thing we do not understand, something about the time at which the phase center is normal to the chosen UV plane for phasing
Orientation of the physical dipole corresponding to what is labelled as the x polarization. Options are “east” (indicating east/west orientation) and “north” (indicating north/south orientation)
last updated: 2020-10-07