Examination of the layer model of the frequency-domain interferometry theory applied in mesosphere-stratosphere-troposphere radars

The thickness and position of an atmospheric layer embedded in the radar vo lume can be resolved by using the frequency-domain interferometry (FDI) tec hnique in accordance with an analytical expression, in which a single layer with Gaussian shape is assumed. However, the FDI experimental results obta ined from the Chung-Li VHF radar show that the layer thickness is usually d ependent on the layer position. In view of this, an attempt is made in this paper to interpret the observations. With the help of numerical simulation , we examine three FDI models: (1) a non-Caussian layer, (2) single layer i n company with background scatterers, and (3) multiple layers. The analytic al FDI expression derived from the Gaussian-layer model is employed in the numerical study to calculate the layer position and layer thickness on the basis of the coherence and phase estimated from the examined layer model. I t shows that the resultant thickness and position of the FDI layer are depe ndent on each other, which is in agreement with the observed thickness-posi tion relations shown in this paper. Moreover, the numerical results can als o provide a reasonable interpretation of the observations reported by earli er scientific workers, such as the discrepancy between the vertical displac ement velocity of the layer and the vertical Doppler velocity, the differen ce in thickness between the FDI-derived layer and in situ observed temperat ure/humidity sheets, etc. We finally illustrate that the range weighting ef fect of the radar system plays a crucial role in the FDI-derived thickness- position relations. (C) 2001 Elsevier Science Ltd. All rights reserved.