Preprints
https://doi.org/10.5194/amt-2022-337
https://doi.org/10.5194/amt-2022-337
 
02 Jan 2023
02 Jan 2023
Status: this preprint is currently under review for the journal AMT.

Using Optimal Estimation to Retrieve Winds from VAD scans by a Doppler Lidar

Sunil Baidar1,2, Timothy J. Wagner3, David D. Turner4, and W. Alan Brewer2 Sunil Baidar et al.
  • 1Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO 80309, USA
  • 2Chemical Sciences Laboratory, National Oceanic and Atmospheric Administration, Boulder, Colorado 80305 USA
  • 3Space Science and Engineering Center, University of Wisconsin-Madison, Madison, Wisconsin 53706 USA
  • 4Global Systems Laboratory, National Oceanic and Atmospheric Administration, Boulder, Colorado 80305 USA

Abstract. Low-powered commercially-available coherent Doppler lidar (CDL) provides continuous measurement of vertical profiles of wind in the lower troposphere, usually close to or up to the top of the planetary boundary layer. The vertical extent of these wind profiles is limited by the availability of scatterers, and thus varies substantially throughout the day and from one day to the next. This makes it challenging to develop continuous products that rely on CDL-observed wind profiles. In order to overcome this problem, we have developed a new method for wind profile retrievals from CDL that combines the traditional velocity-azimuth display (VAD) technique with optimal estimation (OE) to provide continuous wind profiles up to 3 km. The new method exploits the level-to-level covariance present in the wind profile to fill in the gaps where the signal to noise ratio of the CDL return is too low to provide reliable results using the traditional VAD method. Another advantage of the new method is that it provides the full error covariance matrix of the solution and profiles of information content, which more easily facilitates the assimilation of the observed wind profiles into numerical weather prediction models. This method was tested using CDL measurements at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) Central Facility. Comparison with the ARM operational CDL wind profile product and collocated radiosonde wind measurements shows excellent agreement (R2 > 0.99) with no degradation in results where the traditional VAD provided a valid solution. In the region where traditional VAD do not provide results, the OE wind speed has uncertainty of 4.5 m/s. As a result, the new method provides additional information over the standard technique and increases the effective range of existing CDL systems without the need for additional hardware.

Sunil Baidar et al.

Status: open (until 26 Feb 2023)

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Sunil Baidar et al.

Sunil Baidar et al.

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Short summary
This paper provides a new method for retrieving wind profile from Coherent Doppler Lidar (CDL) measurements. It takes advantage of layer-to-layer correlation in wind profiles to fill in the gaps, where CDL signal is too small, to provide continuous wind profiles up to 3 km. Comparison with current method and collocated radiosonde wind measurements showed excellent agreement with no degradation in results where the current method provides a valid results.