Posters

Abstract

Scanning lidars are becoming popular for resource assessment due to their high accuracy, flexibility in scan configurations, and long-range capabilities. A typical dual-Doppler setup, where beams from two lidars intersect at 3–5 points, is commonly used for wind resource assessment. However, in pulsed lidar technology, the line-of-sight velocity is available for all gates simultaneously, yet traditionally only the gates at the intersections are utilized. This study investigates whether non-collocated range gates, using flow homogeneity, can be leveraged to reconstruct wind speed and TI, potentially offering more spatial data than the typical 3–5 measurement points. To address this, we quantify the baseline uncertainty in wind speed and TI using 1 Hz cup anemometer measurements and compare them with dual-Doppler lidar observations. Because multi-point measurements increase the revisit time, we use the same dataset to investigate the impact of artificially reduced sampling rates on measurement accuracy. Finally, we examine how the separation distance between the two range gates affects the reconstructed wind speed and TI. The field campaign was conducted on the east coast of the UK. In the first phase, scanning lidars were programmed to stare at a met mast and measure wind speed and TI at ranges of 5–6 km with a sampling frequency of 1 Hz. Results show that wind speed can be accurately reconstructed with a mean deviation of 0.0011 m/s for wind speeds between 4 and 12 m/s. When the sampling frequency was reduced (to revisit each point every 12 seconds, corresponding to 4 dual-Doppler points), the standard deviation of wind speed deviations increased across all wind speeds. TI was systematically underestimated by approximately 0.007, remaining consistent across sampling rates. Reducing the sampling rate increased the spread of deviations, particularly at lower wind speeds.     Wind speed TI Sampling frequency 1 Hz 1/12 Hz 1 Hz 1/12 Hz Deviation 0.0011 -0.0043 -0.0076 -0.0068 Spread of deviation (std) 0.14734 0.4095 0.0143 (4-8 m/s), 0.0236 (4-8 m/s), 0.0063 (8-12 m/s) 0.0121 (8-12 m/s)   In the second phase of the campaign, the scanning configuration of one lidar was altered to include four stop-and-stare points: one intersecting the second lidar’s beam and three at separation distances of 0.5 km, 1 km, and 1.5 km at the same height. Wind speed and TI reconstruction at these points were compared to reference values at the intersection. Deviations from the reference increased with separation distance but remained consistent with first-phase results when using a matched sampling frequency, up to 1 km. The study concludes that non-collocated range gates can effectively reconstruct mean wind speed and TI up to 1 km in offshore conditions, provided elevation angles are not too steep, which could introduce significant height discrepancies. This methodology offers more representative statistics than traditional approaches by utilizing greater spatial data.     Wind speed [m/s] TI [-] Separation distance 0.5 km 1 km 1.5 km 0.5 km 1 km 1.5 km Deviation -0.0243 -0.0551 -0.1362 0.0017 0.0031 0.0063 Spread of deviation (std) 0.3184 0.3883 0.4859 0.0193 0.0229 0.0254