Exploring dual-lidar mean and turbulence measurements over Perdigão's complex terrain
<p>To assess the accuracy of lidars in measuring mean wind speed and turbulence at large distances above the ground as an alternative to tall and expensive meteorological towers, we evaluated three dual-lidar measurements in virtual-mast (VM) mode over the complex terrain of the Perdigão-2017...
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Copernicus Publications
2025-01-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://amt.copernicus.org/articles/18/287/2025/amt-18-287-2025.pdf |
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| author | I. L. Coimbra J. Mann J. M. L. M. Palma V. T. P. Batista |
| author_facet | I. L. Coimbra J. Mann J. M. L. M. Palma V. T. P. Batista |
| author_sort | I. L. Coimbra |
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| description | <p>To assess the accuracy of lidars in measuring mean wind speed and turbulence at large distances above the ground as an alternative to tall and expensive meteorological towers, we evaluated three dual-lidar measurements in virtual-mast (VM) mode over the complex terrain of the Perdigão-2017 campaign. The VMs were obtained by overlapping two coordinated range height indicator scans, prioritising continuous vertical measurements at multiple heights at the expense of high temporal and spatial synchronisation. Forty-six days of results from three VMs (VM1 on the SW ridge, VM2 in the valley, and VM3 on the NE ridge) were compared against sonic readings (at 80 and 100 <span class="inline-formula">m</span> a.g.l.) in terms of 10 <span class="inline-formula">min</span> means and variances to assess accuracy and the influence of atmospheric stability, vertical velocity, and sampling rate on VM measurements. For mean flow quantities – wind speed (<span class="inline-formula"><i>V</i><sub>h</sub></span>) and <span class="inline-formula"><i>u</i></span> and <span class="inline-formula"><i>v</i></span> velocity components – the <span class="inline-formula"><i>r</i><sup>2</sup></span> values were close to 1 at all VMs, with the lowest equal to 0.948, whereas in the case of turbulence measurements (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" display="inline" overflow="scroll" dspmath="mathml"><mrow><msup><mi>u</mi><mo>′</mo></msup><msup><mi>u</mi><mo>′</mo></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="22pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="175047d0c6687ee2e4ebddc0fafc2677"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-18-287-2025-ie00001.svg" width="22pt" height="11pt" src="amt-18-287-2025-ie00001.png"/></svg:svg></span></span> and <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mrow><msup><mi>v</mi><mo>′</mo></msup><msup><mi>v</mi><mo>′</mo></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="21pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="716e4068f348c1250f139d0cb4b1cea3"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-18-287-2025-ie00002.svg" width="21pt" height="11pt" src="amt-18-287-2025-ie00002.png"/></svg:svg></span></span>), the lowest was 0.809. Concerning differences between ridge and valley measurements, the average RMSE for the wind variances was 0.295 <span class="inline-formula">m<sup>2</sup> s<sup>−2</sup></span> at the VMs on the ridges. In the valley, under a more complex and turbulent flow, smaller between-beam angle, and lower lidars' synchronisation, VM2 presented the highest variance RMSE, 0.600 <span class="inline-formula">m<sup>2</sup> s<sup>−2</sup></span> for <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow><msup><mi>u</mi><mo>′</mo></msup><msup><mi>u</mi><mo>′</mo></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="22pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="2f47087a259cfa593d793f1274636f43"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-18-287-2025-ie00003.svg" width="22pt" height="11pt" src="amt-18-287-2025-ie00003.png"/></svg:svg></span></span>. The impact of atmospheric stability on VM measurements also varied by location, especially for the turbulence variables. VM1 and VM3 exhibited better statistical metrics of the mean and turbulent wind under stable conditions, whereas at VM2, the better results with a stable atmosphere were restricted to the wind variances. We suspect that with a stable and less turbulent atmosphere, the scan synchronisation in the dual-lidar systems had a lower impact on the measurement accuracy. The impact of the zero vertical velocity assumption on dual-lidar retrievals at 80 and 100 <span class="inline-formula">m</span> a.g.l. in Perdigão was minimal, confirming the validity of the VM results at these heights. Lastly, the VMs' low sampling rate contributed to 33 <span class="inline-formula">%</span> of the overall RMSE for mean quantities and 78 <span class="inline-formula">%</span> for variances at 100 <span class="inline-formula">m</span> a.g.l., under the assumption of a linear influence of the sampling rate on the dual-lidar error. Overall, the VM results showed the ability of this measurement methodology to capture mean and turbulent wind characteristics under different flow conditions and over mountainous terrain. Upon appraisal of the VM accuracy based on sonic anemometer measurements at 80 and 100 <span class="inline-formula">m</span> a.g.l., we obtained vertical profiles of the wind up to 430 <span class="inline-formula">m</span> a.g.l. To ensure dual-lidar measurement reliability, we recommend a 90<span class="inline-formula">°</span> angle between beams and a sampling rate of at least 0.05 <span class="inline-formula">Hz</span> for mean and 0.2 <span class="inline-formula">Hz</span> for turbulent flow variables.</p> |
| format | Article |
| id | doaj-art-c08e142f8d4e4ce3b29d357433ff1a83 |
| institution | Kabale University |
| issn | 1867-1381 1867-8548 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Measurement Techniques |
| spelling | doaj-art-c08e142f8d4e4ce3b29d357433ff1a832025-01-16T11:53:14ZengCopernicus PublicationsAtmospheric Measurement Techniques1867-13811867-85482025-01-011828730310.5194/amt-18-287-2025Exploring dual-lidar mean and turbulence measurements over Perdigão's complex terrainI. L. Coimbra0J. Mann1J. M. L. M. Palma2V. T. P. Batista3Faculdade de Engenharia da Universidade do Porto, University of Porto (UPORTO), Rua Dr Roberto Frias s/n, 4200-465 Porto, PortugalDepartment of Wind and Energy Systems, Technical University of Denmark (DTU), Frederiksborgsvej 399, 4000 Roskilde, DenmarkFaculdade de Engenharia da Universidade do Porto, University of Porto (UPORTO), Rua Dr Roberto Frias s/n, 4200-465 Porto, PortugalFaculdade de Engenharia da Universidade do Porto, University of Porto (UPORTO), Rua Dr Roberto Frias s/n, 4200-465 Porto, Portugal<p>To assess the accuracy of lidars in measuring mean wind speed and turbulence at large distances above the ground as an alternative to tall and expensive meteorological towers, we evaluated three dual-lidar measurements in virtual-mast (VM) mode over the complex terrain of the Perdigão-2017 campaign. The VMs were obtained by overlapping two coordinated range height indicator scans, prioritising continuous vertical measurements at multiple heights at the expense of high temporal and spatial synchronisation. Forty-six days of results from three VMs (VM1 on the SW ridge, VM2 in the valley, and VM3 on the NE ridge) were compared against sonic readings (at 80 and 100 <span class="inline-formula">m</span> a.g.l.) in terms of 10 <span class="inline-formula">min</span> means and variances to assess accuracy and the influence of atmospheric stability, vertical velocity, and sampling rate on VM measurements. For mean flow quantities – wind speed (<span class="inline-formula"><i>V</i><sub>h</sub></span>) and <span class="inline-formula"><i>u</i></span> and <span class="inline-formula"><i>v</i></span> velocity components – the <span class="inline-formula"><i>r</i><sup>2</sup></span> values were close to 1 at all VMs, with the lowest equal to 0.948, whereas in the case of turbulence measurements (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" display="inline" overflow="scroll" dspmath="mathml"><mrow><msup><mi>u</mi><mo>′</mo></msup><msup><mi>u</mi><mo>′</mo></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="22pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="175047d0c6687ee2e4ebddc0fafc2677"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-18-287-2025-ie00001.svg" width="22pt" height="11pt" src="amt-18-287-2025-ie00001.png"/></svg:svg></span></span> and <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mrow><msup><mi>v</mi><mo>′</mo></msup><msup><mi>v</mi><mo>′</mo></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="21pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="716e4068f348c1250f139d0cb4b1cea3"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-18-287-2025-ie00002.svg" width="21pt" height="11pt" src="amt-18-287-2025-ie00002.png"/></svg:svg></span></span>), the lowest was 0.809. Concerning differences between ridge and valley measurements, the average RMSE for the wind variances was 0.295 <span class="inline-formula">m<sup>2</sup> s<sup>−2</sup></span> at the VMs on the ridges. In the valley, under a more complex and turbulent flow, smaller between-beam angle, and lower lidars' synchronisation, VM2 presented the highest variance RMSE, 0.600 <span class="inline-formula">m<sup>2</sup> s<sup>−2</sup></span> for <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow><msup><mi>u</mi><mo>′</mo></msup><msup><mi>u</mi><mo>′</mo></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="22pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="2f47087a259cfa593d793f1274636f43"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-18-287-2025-ie00003.svg" width="22pt" height="11pt" src="amt-18-287-2025-ie00003.png"/></svg:svg></span></span>. The impact of atmospheric stability on VM measurements also varied by location, especially for the turbulence variables. VM1 and VM3 exhibited better statistical metrics of the mean and turbulent wind under stable conditions, whereas at VM2, the better results with a stable atmosphere were restricted to the wind variances. We suspect that with a stable and less turbulent atmosphere, the scan synchronisation in the dual-lidar systems had a lower impact on the measurement accuracy. The impact of the zero vertical velocity assumption on dual-lidar retrievals at 80 and 100 <span class="inline-formula">m</span> a.g.l. in Perdigão was minimal, confirming the validity of the VM results at these heights. Lastly, the VMs' low sampling rate contributed to 33 <span class="inline-formula">%</span> of the overall RMSE for mean quantities and 78 <span class="inline-formula">%</span> for variances at 100 <span class="inline-formula">m</span> a.g.l., under the assumption of a linear influence of the sampling rate on the dual-lidar error. Overall, the VM results showed the ability of this measurement methodology to capture mean and turbulent wind characteristics under different flow conditions and over mountainous terrain. Upon appraisal of the VM accuracy based on sonic anemometer measurements at 80 and 100 <span class="inline-formula">m</span> a.g.l., we obtained vertical profiles of the wind up to 430 <span class="inline-formula">m</span> a.g.l. To ensure dual-lidar measurement reliability, we recommend a 90<span class="inline-formula">°</span> angle between beams and a sampling rate of at least 0.05 <span class="inline-formula">Hz</span> for mean and 0.2 <span class="inline-formula">Hz</span> for turbulent flow variables.</p>https://amt.copernicus.org/articles/18/287/2025/amt-18-287-2025.pdf |
| spellingShingle | I. L. Coimbra J. Mann J. M. L. M. Palma V. T. P. Batista Exploring dual-lidar mean and turbulence measurements over Perdigão's complex terrain Atmospheric Measurement Techniques |
| title | Exploring dual-lidar mean and turbulence measurements over Perdigão's complex terrain |
| title_full | Exploring dual-lidar mean and turbulence measurements over Perdigão's complex terrain |
| title_fullStr | Exploring dual-lidar mean and turbulence measurements over Perdigão's complex terrain |
| title_full_unstemmed | Exploring dual-lidar mean and turbulence measurements over Perdigão's complex terrain |
| title_short | Exploring dual-lidar mean and turbulence measurements over Perdigão's complex terrain |
| title_sort | exploring dual lidar mean and turbulence measurements over perdigao s complex terrain |
| url | https://amt.copernicus.org/articles/18/287/2025/amt-18-287-2025.pdf |
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