The authors address the problem of evaluating the normalised radar cross section (NRCS) of the sea surface perturbed by the joint effect of rain and wind, when observed close to nadir. They present a model, based on the full wave theory, for evaluating such an NRCS when varying polarisation, frequency and incidence angle (not far from nadir) for different values of wind velocity and of the root mean square height of the corrugation induced by rainfall. Some comparisons are made with the integral equation model results in the case of rain-induced corrugation alone. The two models are found to be in good agreement. In addition, partial comparisons made with experimental data suggest that the proposed model is well grounded and exploitable for application. It is indeed expected that the model can be exploited to improve precipitation measurements over the sea through spaceborne rain radar and to improve wind measurements using scatterometers in the presence of rain. © IEE, 1998.

The problem of improving estimates of rainfall intensity over the sea surface through spaceborne rain radars is addressed. The backscattered signal is composed of volumetric contribution due to rainfall and of the sea surface contribution. When trying to estimate the NRCS of the sea surface, one of the major difficulties is that different scale of roughness of the sea surface should be accounted for in the same e.m. model: the larger due to wind and the smaller due to the raindrop splashes. While in the first case several models are available in the literature, in the second case only a few experimental results or theoretical studies are at disposal. In this paper, a model which accounts for the additional roughness due to the effects of the raindrop splashes is analysed. Furthermore, an enhanced algorithm is proposed here for retrieving rainfall rate profiles, which utilises the relationship between sea NRCS and rainfall rate.

The prediction of the power backscattered by the sea surface in the presence of rainfall is the object of this paper. An electromagnetic (e.m.) model predicting Normalized Radar Cross Section (NRCS) of such surface, must conveniently account for both a large scale roughness roughness due to wind and a small scale roughness due to raindrop splashes. While several models are available in the literature for wind-induced roughness, only few experimental results or theoretical studies concerning additional rainfall-induced roughness are available. Here we describe an e.m. model that accounts for the effects of the raindrop splashes, and discuss some related results. An improved algorithm is then proposed here for retrieving rainfall rate profiles by means of spaceborne rain radars, which utilizes the relationship between sea NRCS and rainfall rate.

In this paper the problem of improving techniques for rainfall intensity estimation over the sea surface through spaceborne rain radars is analysed. In such case, the backscattered signal is composed of a rainfall volumetric contribution and of the sea surface contribution, which gives rise to the problem of extracting the information of interest from the composite echo. In particular, we focus on the problem of deriving a better estimation of the rain perturbed backscattering coefficient of the sea surface from polarimetric measurements, as a means for achieving such improvements. The effects of the additional roughness of the sea surface due to the rainfall have been taken into account and analysed by resorting to an electromagnetic model able to provide a full polarimetric description of the rainfall perturbed sea surface.

Vertical rainfall profile retrieval based on reflectivity data collected by spaceborne rain radars can be improved through the techniques that exploit an estimation of the sea surface Normalised Radar Cross Section (NRCS) as an additional information. However, errors that can currently be made in predicting the sea surface NRCS may significantly affect their performance. Therefore, in this paper we first address the problem to evaluate the NCRS of the sea surface perturbed by rain, when observed at nadir. For this purpose, the dominant effect of ring waves generated by rainfall is considered. The joint effect of wind is also considered. The proposed model is based on the Full Wave Model (FWM) theory. Some comparisons are made with an alternative, less flexible model based on the Integral Equation Model (IEM) theory, and partial comparisons are also made with experimental data, which authorize to consider the proposed model well grounded and exploitable for application. Then, we show that the model can be usefully exploited to improve rainfall rate vertical profile retrieval over the sea surface, in the case of nadir looking, single frequency radars.