act.retrievals.compute_winds_from_ppi#

act.retrievals.compute_winds_from_ppi(ds, elevation_name='elevation', azimuth_name='azimuth', radial_velocity_name='radial_velocity', snr_name='signal_to_noise_ratio', intensity_name=None, snr_threshold=0.008, remove_all_missing=False, condition_limit=10000.0, return_ds=None)[source]#

This function will convert a Doppler Lidar PPI scan into vertical distribution of horizontal wind direction and speed.

Code was adapted by Kenneth E Kehoe from code developed by Rob K Newsom. Please see the reference noted below and cite accordingly.

Parameters

  • ds (xarray.Dataset) – The xarray dataset containing PPI scan to be converte into winds.

  • elevation_name (str) – The name of the elevation variable in the dataset.

  • azimuth_name (str) – The name of the azimuth variable in the dataset.

  • radial_velocity_name (str) – The name of the radial velocity variable in the dataset.

  • snr_name (str) – The name of the signal to noise variable in the dataset.

  • intensity_name (str) – The name of the intensity variable in the dataset. If this is set will use intensity instead of signal to noise ratio. variable.

  • snr_threshold (float) – The signal to noise lower threshold used to decide which values to use.

  • remove_all_missing (boolean) – Option to not add a time step in the returned dataset where all values are set to NaN

  • condition_limit (float) – Upper limit used with Normalized data to check if data should be converted from scan signal to noise ration to wind speeds and directions.

  • return_ds (None or xarray.Dataset) – If set to a Xarray Dataset the calculated winds dataset will be concatinated onto this dataset. This is to allow looping over this function for many scans and returning a single dataset.

Returns

ds (xarray.Dataset or None) – The winds converted from PPI scan to horizontal wind speeds and wind directions along with wind speed error and wind direction error. If there is a problem determining the breaks between PPI scans, will return None.

References

Rob K Newsom, Alan W Brewer, James M Wilczak, Daniel E Wolfe, Steven P Oncley and Julie K Lundquist ; Validating Precision Estimates in Horizontal Wind Measurements from a Doppler Lidar, Atmospheric Measurement Techniques Discussions 2016, 10, 1-30

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