Edge technique: theory and application to the lidar measurement of atmospheric wind.

The edge technique is a new and powerful method for measuring small frequency shifts. With the edge technique a laser is located on the steep slope of a high-resolution spectral filter, which produces large changes in transmission for small frequency shifts. A differential technique renders the frequency shift measurement insensitive to both laser and filter frequency jitter and drift. The measurement is shown to be insensitive to the laser width and shape for widths that are less than the half-width of the edge filter. The theory of the measurement is given with application to the lidar measurement of wind. The edge technique can be used to measure wind with a lidar by using either the aerosol or molecular backscattered signal. Examples of both measurements are presented. Simulations for a ground-based lidar at 1.06 microm using reasonable instrumental parameters are used to show an accuracy for the vector components of the wind that is better than 0.5 m/s from the ground to an altitude of 20 km for a 100-m vertical resolution and a 100-shot average. For a 20-m vertical resolution and a 10-shot average, simulations show an accuracy of better than 0.2 m/s in the first 2 km and better than 0.5 m/s to 5 km.