Numerical investigation of intense rainfall effects on coherent and incoherent slant-path propagation at K-band and above

Abstract

A model investigation is carried out to analyze the impact of intense rainfall on slant-path microwave propagation, using a rainfall microphysical model. The effects are evaluated both for path attenuation, undergone by coherent radiation, and for multiple scattering phenomena, originating incoherent radiation along the path. Atmospheric spatial inhomogeneity is taken into account by considering a precipitating-cloud three-dimensional distribution, obtained from the numerical outputs of a microphysical cloud-resolving model. The electromagnetic propagation model is formulated by means of the radiative transfer theory, rigorously defining the forward coherent multiple scattering effect within this framework. The propagation model is applied both to simplified rain slabs and to vertically and horizontally inhomogeneous raining cloud structures in order to compare the impact of atmospheric models on coherent and incoherent propagation. Beacon frequencies between 20-50 GHz are considered together with elevation angles between 20 -40 and surface rain rates from 1 to 100 mm/h. Appropriate sensitivity analysis parameters are defined to present and discuss the numerical results. The main conclusion of this numerical study is that the impact of the convective rainfall structure can be significant both in determining total attenuation and to quantify multiple scattering contribution to the received power. For intense rainfall, the use of a rain slab model can overestimate coherent attenuation and, at the same time, underestimate incoherent intensity. The analysis of realistic raining clouds structures reveals the significance of modeling the volumetric albedo of precipitating ice, particularly at V-band. Total path attenuation can strongly depend on the pointing direction of the receiving antenna due to the intrinsic variability of the precipitating cloud composition along the slant path. Coupling cloud-resolving models with radiative transfer schemes may be foreseen as a new approach to develop statistical prediction methods at Ka-band and above in a way analogous to that pursued by using weather-radar volume data.Index Terms-Cloud and rainfall modeling, earth-satellite millimeter-wave links, microwave propagation, multiple scattering effects, radiative transfer theory, rain attenuation.

Characterization of atmospheric precipitation effects on spaceborne synthetic aperture radar response at X, Ku, Ka band

“…The simple precipitation model, previously described, can be made more sophisticated by using a high-resolution cloud resolving models. Among the latter we enumerate: i) the Weather Research and Forecasting (WRF); ii) the Goddard Cumulus Ensemble (GCE) by NASA [Marzano and Roberti, 2003]; iii) the System for Atmospheric Modeling (SAM).…”

Generalized Eddington analytical model for azimuthally dependent radiance simulation in stratified media

“…In the same perspective, once the radiance field is computed from Eqs. (1) at a given position, the received power of an antenna (or detector) with a directive gain G can be derived from 10,13…”

“…The approach, summarized by Eqs. (10), closely resembles the theoretical framework of the discrete ordinate numerical method 30 even though our objective here is to derive a closed-form solution, paying the price of simplifying approximations that will reflect in a less overall accuracy. From Eqs.…”

“…Its full solution can be accomplished by using several numerical techniques that generally reduce the problem to a set of differential equations in a matrix form with prescribed boundary conditions. 13,16,17,10,9 The interest and the importance in developing analytical approximate solutions of the radiative transfer problem arises from the need to have relatively fast algorithms and from the difficulty to derive precise solutions for many practical applications where the medium properties are not generally known with sufficient accuracy. In this respect, uncertainties in the input parameter description within a given radiative transfer problem tend to reduce the need of calculations with a high degree of precision.…”

A model to predict cloud density from midlatitude atmospheric soundings for microwave radiative transfer applications

“…The study is focused on the Mediterranean area, which deserves the attention of a large community. The new cloud density model developed in this paper is based on the outputs of a numerical simulation of a cloudy event, derived from a mesoscale forecast system with explicit cloud microphysics [e.g., d'Auria et al , 1998; Marzano and Roberti , 2003]. Being based on synthetic data, this procedure can be, in principle, applied to any geographical zone where mesoscale simulations are available.…”