act.retrievals.calculate_wavelet_pbl#

act.retrievals.calculate_wavelet_pbl(ds, var_name='wind_speed', range_name='height', scale=60.0, continuity_window=2, min_height=100, max_height=None)[source]#

Estimation of the Planetary Boundary Layer (PBL) height from a ceilometer or Doppler lidar through a Haar wavelet covariance transform. The dataset is averaged into 5-minute periods, and each vertical profile is decomposed with a Haar wavelet. The PBL height at each time is taken to be the range at which the wavelet approximation coefficients show their sharpest transition. A continuity check then replaces PBL height estimates that jump more than 150 m above their neighbors with the local baseline.

Note: This retrieval method should be applied under a cloud-free, well-mixed PBL condition.

It is not expected perform well in cloud capped boundary layers. Additional PRs will be included within the near future to address more PBL environmental conditions.

Parameters:

  • ds (xarray.Dataset) – Dataset containing the zenith-pointing ceilometer or Doppler lidar data.

  • var_name (str) – Variable in the dataset to compute the wavelet transform on (e.g., backscatter intensity or vertical velocity).

  • range_name (str) – Name of the range/height coordinate in the dataset.

  • scale (float) – Approximate spatial scale, in the same units as range_name, over which the Haar wavelet decomposition is performed. This sets the decomposition level.

  • continuity_window (int) – Number of neighboring time steps on each side of a given time to average over when checking for, and smoothing out, discontinuous PBL height estimates.

  • min_height (float) – Minimum allowed PBL height in the units of range_name. Excludes near-surface noise from the search for the sharpest transition.

  • max_height (float or None) – Maximum allowed PBL height in the units of range_name. Use this to exclude elevated cloud or aerosol layers above the PBL from the search. If None, no upper bound is applied.

Returns:

ds (xarray.Dataset) – Dataset resampled to 5-minute periods with new variables wavelet_backscatter, containing the Haar wavelet approximation coefficients, and pbl_wavelet, containing the estimated PBL heights.

References

Brooks, I. M. (2003). Finding boundary layer top using

wavelet covariance transform. Journal of Atmospheric and Oceanic Technology, 20(8), 1092-1105. https://doi.org/10.1175/1520-0426(2003)20%3C1092:FBLTUB%3E2.0.CO;2

Cohn, S. A., & Angevine, W. M. (2000). Boundary layer height and

entrainment zone thickness measured by lidars and wind-profiling radars. Journal of Applied Meteorology, 39(8), 1233-1247. https://doi.org/10.1175/1520-0450(2000)039%3C1233:BLHAEZ%3E2.0.CO;2