the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Suppression of precipitation bias on wind velocity from continuous-wave Doppler lidars
Jakob Mann
Nikolas Angelou
Mikael Sjöholm
Abstract. In moderate to heavy precipitation, rain droplets may deteriorate Doppler lidars' accuracy for measuring the line-of-sight wind velocity because their projected velocity on the beam direction differs greatly from that of air. Therefore, we propose a method of effectively filtering away the adverse effects of rain on velocity estimation by sampling the Doppler spectra faster than the rain drops' beam transit time. By using a special averaging procedure, we can suppress the rain signal by sampling the spectrum at 3 kHz. On a moderately rainy day with a maximum rain intensity of 4 mm/h, three ground-based continuous-wave Doppler lidars were used to conduct a field measurement campaign at the Risø campus of the Technical University of Denmark. We demonstrate that the rain bias can effectively be removed by normalizing the noise-flattened Doppler spectra with their peak values before they are averaged down to 50 Hz prior to the determination of the speed. In comparison to the sonic anemometer measurements acquired at the same location, the wind velocity bias at 50 Hz is reduced from up to −1.58 m/s of the conventional lidar data to −0.18 m/s of the normalized lidar data. This significant reduction of the bias occurs at the minute with the highest amount of rain when the measurement distance of the lidar is 103.9 m with a corresponding probe length being 9.8 m. With the smallest probe length, 1.2 m, the rain-induced bias was only present at the period with the highest rain intensity and was also effectively eliminated with the procedure. Thus the proposed method for reducing the impact of rain on continuous-wave Doppler lidar measurements of air velocity is promising, without requiring much computational effort.
Liqin Jin et al.
Status: open (until 19 Jun 2023)
-
RC1: 'Comment on egusphere-2023-464', Anonymous Referee #1, 13 May 2023
reply
General comments
The authors propose an interesting method of filtering away the adverse effects of rain on velocity estimation by sampling the Doppler spectra faster than the raindrops’ beam transit time. The method is validated with two continuous-wave Doppler lidar measurements. The paper is well-written. I recommend acceptance after minor revisions.
- Lidar #1 has a relatively bigger elevation angle of 57.9◦ compared to Lidar #3 of 15.3◦. Generally, the velocity difference between aerosols and raindrops appears in the vertical direction. Therefore, large elevation angles should suffer more influence from rain signals. While figure 17 exhibits the opposite results (Raw data with the red circle). The authors explain that the short probe length may contribute to it. I think adding a comparison experiment or detailed analysis will be better.
- The proposed method is verified by continuous-wave Doppler lidar measurements. I’m also interested in whether it’s also suitable for a pulsed Doppler lidar which often uses a collimated beam. The author is advised to add related discussions.
Citation: https://doi.org/10.5194/egusphere-2023-464-RC1 -
RC2: 'Comment on egusphere-2023-464', Anonymous Referee #2, 29 May 2023
reply
Liqin Jin et al.
Liqin Jin et al.
Viewed
HTML | XML | Total | BibTeX | EndNote | |
---|---|---|---|---|---|
150 | 55 | 4 | 209 | 1 | 0 |
- HTML: 150
- PDF: 55
- XML: 4
- Total: 209
- BibTeX: 1
- EndNote: 0
Viewed (geographical distribution)
Country | # | Views | % |
---|
Total: | 0 |
HTML: | 0 |
PDF: | 0 |
XML: | 0 |
- 1