Performance Optimization And Wind Field Retrieval For Mobile Wind Lidar

Doppler wind lidar, which has significant advantages of the high spatial and temporal resolution and the ability of measurements in the clear atmosphere, has currently become one of the most effective instruments for wind field measurements. It can provide wind profiles with high accuracy and three dimensional wind fields. In order to propel the routine measurements and applications of Doppler wind lidar as well as reveal its advantages in high spatial and temporal resolution measurements, the main problems within the former Doppler wind lidar decreasing the measurement performance are studied and solved in this dissertation. As a result, the wind retrieval method for wind lidar is improved and the routine measurement is achieved. These works significantly contribute to the development and application of the first mobile wind lidar in China and enable the mobile Doppler lidar to service the Olympic Games.The problem of wind measurements with incoherent Doppler wind lidar during daytime operation and of the fluctuation of the polarization ratio which influences the scanning measurements are studied and solved in this dissertation. The wind retrieval accuracy of wind lidar is enhanced by improving the methods of wind measurement and retrieval. The retrieval of sea surface wind with high accuracy and high spatial and temporal resolution is realized for the first time, which fills in the gaps in other instruments and is applied and validated in the 2007 Qingdao International Regatta (Test Event for 2008 Olympic Sailing Regatta). The concrete scientific contributions of this study are as follows:1. Based on the analysis of the signal-to-noise ratio of incoherent Doppler wind lidar during daytime operation and on the specific optical structures and performance parameters of the system, the system parameters are optimized and the daytime operation within a range of 12 km is achieved by means of matching the laser divergence and field-of-view, using the interference filter with narrow linewidth and restraining the near-field signal by the fiber. Furthermore, with the analysis on the error sources, the errors caused by the fluctuation of the polarization ratio during scanning measurements are reduced by using the non-polarized beamsplitter instead of the normal beamsplitter. As a result, the error of 4-5 m/s in the line-of-sight velocity is almost eliminated, which significantly improves the accuracy of scanning measurements.2. In order to improve the accuracy of wind profile measurements, a method of direct-measurement of sensitivity is proposed based on the analysis of various error sources in the formal retrieval method. This method eliminates the errors of wind speed in the molecular scattering dominated condition due to the atmospheric temperature variation and molecular scattering model. Moreover, when aerosol scattering dominates, the nonlinear correction for the sensitivity is applied to the method of direct-measurement of sensitivity. Therefore, the formal retrieval method is improved and the new method is applied to the routine measurements of the mobile wind lidar.3. According to the requirements of both sea surface wind observations and the Olympic Sailing Regatta, the wind lidar retrieval method for sea surface wind is investigated in this dissertation. The measurement method for line-of-sight velocity applicable to retrieval of sea surface wind is established. Using the VAD correction of line-of-sight velocity, the retrieval of horizontal wind speed by VAP algorithm and the height correction of wind speed, the wind lidar observations of sea surface wind with spatial resolution of 50 m and 100 m and temporal resolution of 2 min and 10 min are obtained in real-time for the first time in the 2007 Qingdao International Regatta (Test Event for 2008 Olympic Sailing Regatta). The comparison with the simultaneous measurements of buoy and wind tower results in the statistical error of 1.1 m/s and 20°of wind speed and direction, respectively. Moreover, several special phenomena of the sea surface wind observed by the mobile wind lidar are presented, which suggest wind lidar has great potential of the application to observe and investigate the microscale weather phenomena.4.Considering the influence of the atmospheric model on the lidar performance and retrieval results, the aerosol optical properties are retrieved based respectively on the Gaussian Model and S6 Model using the data acquired by the airborne high spectral resolution lidar (HSRL) of German Aerospace Center (DLR) in this dissertation. The influences of the two models on the retrieval of aerosol optical properties are compared and the errors due to the Gaussian Model are quantified. It suggests that the errors due to the Gaussian Model are comparable to the total systematic error, which should be taken into account during the retrieval of atmospheric parameters and the performance analysis of lidar systems. This research work has important reference value in parameter design and performance analysis for both ground and space based HSRLs and wind lidars.