pyart.correct.dealias_fourdd#

pyart.correct.dealias_fourdd(radar, last_radar=None, sonde_profile=None, gatefilter=False, filt=1, rsl_badval=131072.0, keep_original=False, set_limits=True, vel_field=None, corr_vel_field=None, last_vel_field=None, debug=False, max_shear=0.05, sign=1, **kwargs)[source]#

Dealias Doppler velocities using the 4DD algorithm.

Dealias the Doppler velocities field using the University of Washington 4DD algorithm utilizing information from a previous volume scan and/or sounding data. Either last_radar or sonde_profile must be provided. For best results provide both a previous volume scan and sounding data. Radar and last_radar must contain the same number of rays per sweep.

Additional arguments are passed to _fourdd_interface.fourdd_dealias(). These can be used to fine tune the behavior of the FourDD algorithm. See the documentation of Other Parameters for details. For the default values of these parameters see the documentation of _fourdd_interface.fourdd_dealias().

Parameters:

  • radar (Radar) – Radar object to use for dealiasing. Must have a Nyquist defined in the instrument_parameters attribute and have a reflectivity_horizontal and mean_doppler_velocity fields.

  • last_radar (Radar, optional) – The previous radar volume, which has been successfully dealiased. Using a previous volume as an initial condition can greatly improve the dealiasing, and represents the final dimension in the 4DD algorithm.

  • sonde_profile (HorizontalWindProfile, optional) – Profile of horizontal winds from a sonding used for the initial condition of the dealiasing.

Other Parameters:

  • gatefilter (GateFilter, optional.) – A GateFilter instance which specifies which gates should be ignored when performing velocity dealiasing. A value of None will create this filter from the radar moments using any additional arguments by passing them to moment_based_gate_filter(). The default value assumes all gates are valid.

  • filt (int, optional) – Flag controlling Bergen and Albers filter, 1 = yes, 0 = no.

  • rsl_badval (float, optional) – Value which represents a bad value in RSL.

  • keep_original (bool, optional) – True to keep original doppler velocity values when the dealiasing procedure fails, otherwise these gates will be masked. NaN values are still masked.

  • set_limits (bool, optional) – True to set valid_min and valid_max elements in the returned dictionary. False will not set these dictionary elements.

  • vel_field (str, optional) – Field in radar to use as the Doppler velocities during dealiasing. None will use the default field name from the Py-ART configuration file.

  • corr_vel_field (str, optional) – Name to use for the dealiased Doppler velocity field metadata. None will use the default field name from the Py-ART configuration file.

  • last_vel_field (str, optional) – Name to use for the dealiased Doppler velocity field metadata in last_radar. None will use the corr_vel_field name.

  • maxshear (float, optional) – Maximum vertical shear which will be incorporated into the created volume from the sounding data. Parameter not used when no sounding data is provided.

  • sign (int, optional) – Sign convention which the radial velocities in the volume created from the sounding data will will. This should match the convention used in the radar data. A value of 1 represents when positive values velocities are towards the radar, -1 represents when negative velocities are towards the radar.

  • compthresh (float, optional) – Fraction of the Nyquist velocity to use as a threshold when performing continuity (initial) dealiasing. Velocities differences above this threshold will not be marked as gate from which to begin unfolding during spatial dealiasing.

  • compthresh2 (float, optional) – The same as compthresh but the value used during the second pass of dealiasing. This second pass is only performed in both a sounding and last volume are provided.

  • thresh (float, optional) – Fraction of the Nyquist velocity to use as a threshold when performing spatial dealiasing. Horizontally adjacent gates with velocities above this threshold will count against assigning the gate in question the velocity value being tested.

  • ckval (float, optional) – When the absolute value of the velocities are below this value they will not be marked as gates from which to begin unfolding during spatial dealiasing.

  • stdthresh (float, optional) – Fraction of the Nyquist velocity to use as a standard deviation threshold in the window dealiasing portion of the algorithm.

  • epsilon (float, optional) – Difference used when comparing a value to missing value, changing this from the default is not recommended.

  • maxcount (int, optional) – Maximum allowed number of fold allowed when unfolding velocities.

  • pass2 (int, optional) – Controls weather unfolded gates should be removed (a value of 0) or retained for unfolding during the second pass (a value of 1) when both a sounding volume and last volume are provided.

  • rm (int, optional) – Determines what should be done with gates that are left unfolded after the first pass of dealiasing. A value of 1 will remove these gates, a value of 0 sets these gates to their initial velocity. If both a sounding volume and last volume are provided this parameter is ignored.

  • proximity (int, optional) – Number of gates and rays to include of either side of the current gate during window dealiasing. This value may be doubled in cases where a standard sized window does not capture a sufficient number of good valued gates.

  • mingood (int, optional) – Number of good valued gates required within the window before the current gate will be unfolded.

  • ba_mincount (int, optional) – Number of neighbors required during Bergen and Albers filter for a given gate to be included, must be between 1 and 8, 5 recommended.

  • ba_edgecount (int, optional) – Same as ba_mincount but used at ray edges, must be between 1 and 5, 3 recommended.

  • debug (bool, optional) – Set True to return RSL Volume objects for debugging: usuccess, radialVelVolume, lastVelVolume, unfoldedVolume, sondVolume

Returns:

vr_corr (dict) – Field dictionary containing dealiased Doppler velocities. Dealiased array is stored under the ‘data’ key.

Notes

Due to limitations in the C code do not call with sounding arrays over 999 elements long.

References

C. N. James and R. A Houze Jr, A Real-Time Four-Dimensional Doppler Dealising Scheme, Journal of Atmospheric and Oceanic Technology, 2001, 18, 1674.