Sunday, 9 January 2005
Evaluating various wind measurement and retrieval schemes used for the Pentagon Shield Project
The Pentagon Shield Project is an antiterrorist initiative to develop a system that models and predicts the dispersion of airborne toxins around the Pentagon. This system will depend on wind measuring instruments and estimation, or retrieval, techniques to provide input to dispersion models. A field experiment conducted in April-May 2004 used a number of wind measuring instruments and retrieval techniques to examine the local airflow. This study evaluated the accuracy of two measuring instruments, Doppler lidar (a laser-based radar) and SODAR (SOund Detection And Ranging), and three retrieval techniques to determine which schemes provide the most reliable wind profiles. The data were compared by separating the observed and retrieved wind vectors into two components, the radial and azimuthal components. A least-square fit comparison of the radial wind components from the lidar and SODAR showed that the SODAR-measured winds were slightly higher than those measured by the lidar. The azimuthal wind components were used to verify the retrieval techniques, Velocity-Azimuth Display (VAD) and two variations of Velocity Volume Processing (VVP-1, VVP-2). Our results showed that the VAD method breaks down for the small sectors of data that were collected over the Pentagon. VVP-1 and VVP-2 perform least-square curve fitting on radial wind data but over different sectors. The results showed that VVP-2 gives a better estimate of the average wind over larger areas. Evaluating these schemes is important not only for the Pentagon Shield Project, but for other studies that use similar instruments and techniques to examine wind fields.