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

Abstract

irborne 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.