Scattering layer thickness and position estimated by radar frequency domain interferometry - 2. Effects of tilts of the scattering layer or radar beam

In the companion paper (part 1), theoretical studies on the dual frequency domain interferometry (FDI) technique have been presented. Two possible cau ses of biases in the layer thickness and position estimations by FDI have b een considered: the limited extent of the scattering structure in the horiz ontal plane and the advection of this structure by the wind. In the present work, we study the effects of the tilts of the scattering layer from horiz ontal. It is shown that in case of large tilt angles, substantial biases on position and thickness can occur. The model, first developed by Liu and Pa n [1993] but more extensively described in this paper, can also be used for a prediction of the variations of the FDI coherence with the zenith angle and their relation to the anisotropy of the scatterers. Some preliminary ob servations of the zenith angle dependence of the FDI coherence and echo pow er obtained with the middle and upper atmosphere (MU) radar from the vertic al up to 28 degrees off zenith with a step of 2 degrees are shown and discu ssed. In principle, comparisons between the observed power and coherence va riations with those given by the model could give more information on the s tructures that contribute around and far from the zenith.