Scattering layer thickness and position estimated by radar frequency domain interferometry 1. Effects of the limited horizontal extent and advection of the scattering layers

Frequency domain interferometry (FDI) is a mesosphere-stratosphere-troposph ere radar technique used for probing thin-layered structures of the atmosph ere. The position and thickness of a scattering layer embedded within the i lluminated volume can be deduced from the complex coherence of received sig nals at two closely spaced frequencies. This technique has permitted us to identify layered structures (called "FDI layers") with thicknesses estimate d to be around 50-200 m in the troposphere-stratosphere. However, its appli cation needs very restrictive hypotheses. For example, the layers are assum ed to have a large extent in the horizontal plane with respect to the horiz ontal extent defined by the -6-dB angular width of the two-way antenna patt ern. This hypothesis seems not always to be verified in light of observatio ns with other radar techniques. In this paper, theoretical calculations are performed in order to estimate the consequences of the limited extent of t he scattering structure in the horizontal plane on the FDI parameters, i.e. the vertical extent and position in height of the single layer. The first analysis concerns the effects of the limited extent by itself, and the seco nd one deals with the consequences of the advection of the scattering struc ture by the wind. It is shown that in some limiting cases, substantial bias es in the FDI parameters can occur. Finally, this work stresses the necessi ty to confront the FDI data with other technique measurement results or to complete it with space domain interferometry data. A future paper will be d evoted to the study of the effects of the tilt of a scattering layer on the thickness and position estimations.