Cloud and precipitation filter - BLVIEW - CL61

BL-View for CL61 User Guide

Document code
Document type
User guide

Cloud filters prevent spurious mixing height retrievals caused by clouds or precipitation in the backscatter profiles, especially below 4000 m (13 123 ft) above ground level.

  • In the gradient method, clouds and precipitation produce strong local gradients that may be unrelated to the mixing height.
  • In the profile fit method, clouds and precipitation produce backscattering profiles that deviate substantially from an idealized profile, which result in poor mixing height estimates.

The cloud filter significantly improves the mixing height estimate, and eliminates retrievals in the morning when there are clouds and strong backscatter near the ground.

The algorithm does not report a mixing height when one or more of the following circumstances exists:

  1. Clouds are present below 160 m (525 ft) above ground level.
  2. Precipitation or excessively high backscatter are detected in the backscatter profile.
  3. Clouds are present below 4000 m (13 123 ft) above ground level and there is excessive backscatter below 1000 m (3280 ft). Retrievals are still allowed when there are shallow, non-precipitating clouds below 4000 m (13 123 ft), but above 160 m (525 ft).