A Potential Source of Bias in Horizontal Winds Estimated Using a 915-MHz Acoustically Enhanced Profiler

Clear-air Doppler wind profilers perform poorly in dry, calm conditions when reflectivities are low. One solution to this problem is to use acoustic waves, generated by a collocated acoustic source, as the scattering target instead of clear-air turbulence. The idea for such an acoustically enhanced profiler was proposed more than 10 years ago. In a recent Antarctic experimental campaign, a vertically pointing acoustic source was used to extend the coverage of a standard four-beam 915-MHz wind profiler. Preliminary testing of the system revealed large biases in the retrieved wind profiles. A simple theory and a limited dataset suggest that the observed biases are consistent with a nonuniform acoustic illumination of the radar beams caused by the different acoustic and radar beam pointing angles. Our results suggest that this bias can be eliminated by aligning the acoustic and radar beams.