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

The thickness and position of an atmospheric layer embedded in the radar volume can be resolved by using the frequency-domain interferometry (FDI) technique in accordance with an analytical expression, in which a single layer with Gaussian shape is assumed. However, the FDI experimental results obtained from the Chung-Li VHF radar show that the layer thickness is usually dependent 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-Gaussian layer, (2) single layer in company with background scatterers, and (3) multiple layers. The analytical 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. It shows that the resultant thickness and position of the FDI layer are dependent on each other, which is in agreement with the observed thickness-position relations shown in this paper. Moreover, the numerical results can also provide a reasonable interpretation of the observations reported by earlier scientific workers, such as the discrepancy between the vertical displacement velocity of the layer and the vertical Doppler velocity, the difference in thickness between the FDI-derived layer and in situ observed temperature/humidity sheets, etc. We finally illustrate that the range weighting effect of the radar system plays a crucial role in the FDI-derived thickness-position relations.