Retrieving Winds in the Surface Layer over Land Using an Airborne Doppler Lidar

Abstract

Airborne Doppler wind lidars are increasingly being used to measure winds in the lower atmosphere at higher spatial resolution than ever before. However, wind retrieval in the range gates closest to the earth’s surface remains problematic. When a laser beam from a nadir-pointing airborne Doppler wind lidar intercepts the ground, the return signal from the ground mixes with the windblown aerosol signal. As a result, winds in a layer adjacent to the surface are often unreliable and removed from wind profiles. This paper describes the problem in detail and discusses a two-step approach to improve near-surface wind retrievals. The two-step approach involves removing high-intensity ground returns and identifying and tracking aerosol radial velocities in the layer affected by ground interference. Using this approach, it is shown that additional range gates closer to the surface can be obtained, thereby further enhancing the potential of airborne Doppler lidar in atmospheric applications. The benefits of the two-step approach are demonstrated using measurements acquired over the Salinas Valley in central California. The additional range gates reveal details of the wind field that were previously not quantified with the original approach, such as a pronounced near-surface wind speed maximum.

Airborne Doppler Lidar Measurements of Valley Flows in Complex Coastal Terrain

“…3). Ongoing efforts to improve the retrieval of airborne Doppler lidar winds below 300 m AGL reveal a further increase of the wind speeds near the surface for this case study (Godwin et al 2012). Note that, below 500 m MSL, winds near the coast are westerly (onshore), indicating a clear influence from the sea breeze.…”

“…Because winds could not be faithfully retrieved from Doppler lidar below 300 m AGL, an investigation of the sea-breeze and upvalley wind maxima that occur in this layer and the upslope flows over the sidewalls was not possible. Efforts are ongoing to improve the retrieval of winds in this layer near the surface (Godwin et al 2012). This paper demonstrated the ability of airborne Doppler lidar data to produce a detailed and comprehensive three-dimensional picture of atmospheric features and structure.…”

“…Efforts to improve the retrieval of these winds are ongoing and involve a better identification of the aerosol signal. In some cases, these efforts have resulted in a retrieval of an extra 100 m (Godwin et al 2012). …”

Runway Wake Vortex, Crosswind, and Visibility Detection with a Scintillometer at Schiphol Airport

“…However, Doppler lidars have problems with retrieving the correct wind speed and wind direction near the surface. The reason is that the return signal of the ground also influences the signal (Godwin et al 2012). Hallock and Osgood (2003) showed that wake vortices can also be obtained from a large array of sonic anemometers (in the study of Hallock and Osgood (2003) a sonic every 50 m).…”

An LES-based airborne Doppler lidar simulator for investigation of wind profiling in inhomogeneous flow conditions

“…These systems yield higher spatial resolution (O(1 km) for wind profiling) and enable boundary-layer studies. Thus far, only results for wind profiling of the mean horizontal wind have been reported Godwin et al, 2012;Koch et al, 2014). As of yet, a study analyzing the vertical wind through nadir or other measurement geometries such as Dual-Doppler have not been attempted for the medium-range aircraft.…”