Dual Doppler Lidar Wind Profiling in the Lidar Uncertainty Measurement Experiment (LUMEX)

The Lidar Uncertainty Measurement Experiment (LUMEX) was a cooperative experiment performed during the period of June 23rd to July 13th, 2014. Participants included the National Oceanic and Atmospheric Administration (NOAA); the University of Maryland, Baltimore County (UMBC); the University of Colorado Boulder (CU); and North-West Research Associates (NWRA/CoRA). The primary focus of LUMEX was to bring several different lidars together for inter-comparison, allowing for the determination of measurement uncertainties and relative sensitivity. Turbulence and wind vector retrieval techniques were also tested. LUMEX featured five Doppler lidars of both commercial and research grade. The lidars were brought together at the Boulder Atmospheric Observatory (BAO) tower in Colorado, a three hundred meter tall tower fitted with sonic anemometers at 6 levels and other in situ instruments. This provided many “truth” values for the experiment.

One phase of LUMEX was dedicated to dual Doppler measurements. Dual Doppler is a method of remotely measuring wind speed and direction that utilizes two Doppler lidars, not co-located, simultaneously looking at the same point in space. By applying geometric formulas to the two measured line-of-sight winds, dual Doppler scans can yield the two-dimensional wind vector at a location. By scanning intersecting vertical slices (Range Height Indicator, RHI scans), one can produce a virtual tower of wind speeds at the intersection point. This method, when implemented correctly, can quickly and accurately measure wind speeds in a column over a point in space.

NOAA's High Resolution Doppler Lidar (HRDL) and UMBC's commercially manufactured Leosphere WINDCUBE ™ 200S performed dual Doppler scans for several days during LUMEX, with RHI scans intersecting near the BAO tower as well as directly over a WINDCUBE ™ V1 wind profiling lidar, which uses the Doppler Beam Swinging (DBS) method to estimate wind profiles. The tower and profiling lidar provided accurate measurements against which to compare the dual Doppler results. Two different scan styles were run to observe any measurement improvement with increased time spent at a single virtual tower location.

The data gathered during the dual Doppler phase of LUMEX will be used to test and improve dual Doppler processing code. Also, the strengths and weaknesses of these dual Doppler scanning techniques can be evaluated from this experience, which is valuable for future endeavors. These results and findings as they apply to dual Doppler scanning, wind energy surveying, and the lidar community at large will be discussed in this presentation.