Frequency domain interferometry on spaced antenna MF radar

Frequency domain interferometry (FDI) experiments were carried out on two medium frequency spaced antenna radars located in New Zealand and the Antarctic. These experiments were the first spaced antenna FDI experiments on MF radar and allowed simultaneous measurements of wind, angular distribution, spatial interferometry, FDI range, and scattering depth to be made. It was found that when correcting the FDI scattering depths for the scale of the radar volumes, typically large on MF radars, the adjustment should include a measure of the aspect sensitivity of the scattering. FDI provides a means of clearly identifying thin layers, and the occurrence of such layers often appeared here to be related to fluctuations in the wind. A very interesting example was a thin layer event that seemed to be closely related to a reversal of the wind apparently caused by a change in phase of the semidiurnal tide; enhanced turbulence following the event suggested breaking of the wave. Multiple frequency steps were used and, with analysis by frequency correlation functions, revealed the occasional presence of multiple scattering features in the radar volume.