Fig. 20

(Modified from Briggs 1980). The situation described in the text outlining the basis of the formation of the ground diffraction pattern in the SA experiment. Here, the electric fields produced by volume scatter from a moving atmosphere at angles of ±θ sum to produce an electric field on the ground, the real part of which is a sinusoid of wavelength \( \raisebox{1ex}{$\lambda $}\!\left/ \!\raisebox{-1ex}{$ \sin \theta $}\right. \) that moves with twice the velocity of the atmosphere at the backscatter height. When a broad range of angles is illuminated, the sinusoids from each pair of angles sum to produce the moving ground diffraction pattern. DBS techniques use a narrower angular range of angles (such as those outlined in green) to measure the line of sight Doppler shift. When these are obtained from a number of angles and statistical homogeneity of the wind field is assumed, the three-dimensional wind field can be reconstructed. Interferometric techniques use Doppler shifts associated with randomly distributed scattering centers to determine a mean velocity