Targeted Observations with an Airborne Wind Lidar

Abstract

This study investigates the possibilities and limitations of airborne Doppler lidar for adaptive observations over the Atlantic Ocean. For the first time, a scanning 2-?m Doppler lidar was applied for targeted measurements during the Atlantic ?The Observing System Research and Predictability Experiment? (THORPEX) Regional Campaign (A-TReC) in November and December 2003. The DLR lidar system was operated for 28.5 flight hours, and measured 1612 vertical profiles of wind direction and wind speed with a horizontal and vertical resolution of 5?10 km and 100 m, respectively. On average, there were 25 reliable wind values on every profile, which cover 2500 m in the vertical (about one-third of the mean vertical extent of the profiles). A statistical comparison of 33 dropsondes and collocated lidar winds profiles allowed individual estimates of the standard deviation to be assigned to every wind value and to determine threshold values for an objective quality control of the data. The standard deviation of the difference between dropsonde and lidar winds was correlated with the derived quality indices of the lidar data and was within a range of 0.6?1.8 m s?1. Comparisons of the lidar data to the operational analysis revealed differences of up to ±15 m s?1. This emphasizes the need for more representative and higher resolved wind measurements in data-sparse regions above the Atlantic Ocean. The study constitutes the basis for the assimilation of the lidar data and impact studies at the European Centre for Medium-Range Weather Forecasts (ECMWF).