UVData Parameters

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.

Required

These parameters are required to have a sensible UVData object and are required for most kinds of uv data files.

Nants_data
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
Nants_telescope
Number of antennas in the array. May be larger than the number of antennas with data
Nbls
Number of baselines
Nblts
Number of baseline-times (i.e. number of spectra). Not necessarily equal to Nbls * Ntimes
Nfreqs
Number of frequency channels
Npols
Number of polarizations
Nspws
Number of spectral windows (ie non-contiguous spectral chunks). More than one spectral window is not currently supported.
Ntimes
Number of times
ant_1_array
Array of first antenna indices, shape (Nblts), type = int, 0 indexed
ant_2_array
Array of second antenna indices, shape (Nblts), type = int, 0 indexed
antenna_names
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.
antenna_numbers
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.
baseline_array
Array of baseline indices, shape (Nblts), type = int; baseline = 2048 * (ant2+1) + (ant1+1) + 2^16
channel_width
Width of frequency channels (Hz)
data_array
Array of the visibility data, shape: (Nblts, Nspws, Nfreqs, Npols), type = complex float, in units of self.vis_units
flag_array
Boolean flag, True is flagged, same shape as data_array.
freq_array
Array of frequencies, shape (Nspws, Nfreqs), units Hz
history
String of history, units English
instrument
Receiver or backend. Sometimes identical to telescope_name
integration_time
Length of the integration (s)
lst_array
Array of lsts, center of integration, shape (Nblts), units radians
nsample_array
Number of data points averaged into each data element, NOT required to be an integer. type = float, same shape as data_array
object_name
Source or field observed (string)
phase_type
String indicating phasing type. Allowed values are “drift”, “phased” and “unknown”
polarization_array
Array of polarization integers, shape (Npols). AIPS Memo 117 says: stokes 1:4 (I,Q,U,V); circular -1:-4 (RR,LL,RL,LR); linear -5:-8 (XX,YY,XY,YX)
spw_array
Array of spectral window Numbers, shape (Nspws)
telescope_location
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
telescope_name
Name of telescope (string)
time_array
Array of times, center of integration, shape (Nblts), units Julian Date
uvw_array
Projected baseline vectors relative to phase center, shape (Nblts, 3), units meters
vis_units
Visibility units, options are: “uncalib”, “Jy” or “K str”

Optional

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).

antenna_diameters
Array of antenna diameters in meters. Used by CASA to construct a default beam if no beam is supplied.
antenna_positions
Array giving coordinates of antennas relative to telescope_location (ITRF frame), shape (Nants_telescope, 3)
dut1
DUT1 (google it) AIPS 117 calls it UT1UTC
earth_omega
Earth’s rotation rate in degrees per day
extra_keywords
Any user supplied extra keywords, type=dict
gst0
Greenwich sidereal time at midnight on reference date
phase_center_dec
Required if phase_type = “phased”. Declination of phase center (see uvw_array), units radians. Can also be accessed using phase_center_dec_degrees.
phase_center_epoch
Required if phase_type = “phased”. Epoch year of the phase applied to the data (eg 2000.)
phase_center_ra
Required if phase_type = “phased”. Right ascension of phase center (see uvw_array), units radians. Can also be accessed using phase_center_ra_degrees.
rdate
Date for which the GST0 or whatever… applies
timesys
We only support UTC
uvplane_reference_time
FHD thing we do not understand, something about the time at which the phase center is normal to the chosen UV plane for phasing
x_orientation
Orientation of the physical dipole corresponding to what is labelled as the x polarization. Examples include “east” (indicating east/west orientation) and “north” (indicating north/south orientation)
zenith_dec
Required if phase_type = “drift”. Declination of zenith. units: radians, shape (Nblts). Can also be accessed using zenith_dec_degrees.
zenith_ra
Required if phase_type = “drift”. Right ascension of zenith. units: radians, shape (Nblts). Can also be accessed using zenith_ra_degrees.

last updated: 2017-07-26