Use of Coded Waveforms for SODAR Systems

Summary

Pulse-compression, phase-encoding and chirp techniques are frequently used in EM systems to improve system performance. Simple averaging-over-range and averaging-over frequency schemes have been used in some SODAR systems, but generally code techniques are problematic because of the high fractional Doppler shift of 0–0.04.

The principles of pulse code methods are reviewed with regard to their applicability to SODAR systems. In particular, detailed simulations are performed, using weather-like targets, of a comb of frequencies, a chirp, and a phase-encoding method. Three Doppler-adaptive matched filters are described, and two of these evaluated against the simulated noisy atmosphere. It is found that the comb of frequencies produces the least variance in estimated Doppler wind speed. A filter based on a single evaluation of an FFT for the received signal provides Doppler winds to about 1%. The Doppler-adaptive filters add little computational or hardware overhead, and produce as a simple output a best estimate of the wind speed component.