On the spaced antenna and imaging Doppler interferometer techniques

Abstract

The theory developed by Briggs (1995) is extended to explain the measurement of a wind velocity equivalent to the spaced antenna apparent wind by imaging Doppler interferometer‐like (IDI‐like) interferometric analyses. The point is made that the presence of turbulence, or random change in the diffraction pattern on the ground, is directly responsible for the difference between the true and apparent velocities in the spaced antenna analysis, and also for the overestimation of the wind velocity by the IDI technique. An experiment is conducted to determine whether the “effective” scattering points resolved by IDI‐like analyses tend to lie upon the azimuth predicted by theory. This is found to be the case, even for unsmoothed cross spectra for which the theory was not explicitly derived. An averaging mechanism is proposed which may explain the extent to which the unsmoothed experimental data conform to the behavior predicted by theory.