Bayesian statistical analysis of ground-clutter for the relative calibration of dual polarization weather radars

A new data processing methodology, based on the statistical analysis of ground-clutter echoes and aimed at investigating the stability of the weather radar relative calibration, is presented. A Bayesian classification scheme has been used to identify meteorological and/or ground-clutter echoes. The outcome is evaluated on a training dataset using statistical score indexes through the comparison with a deterministic clutter map. After discriminating the ground clutter areas, we have focused on the spatial analysis of robust and stable returns by using an automated region-merging algorithm. The temporal series of the ground-clutter statistical parameters, extracted from the spatial analysis and expressed in terms of percentile and mean values, have been used to estimate the relative clutter calibration and its uncertainty for both co-polar and differential reflectivity. The proposed methodology has been applied to a dataset collected by a C-band weather radar in southern Italy

Remote sensing and electromagnetic modeling applied to weather and forward scatter radar

This dissertation deals with electromagnetic modelling and data analysis, related to radar remote sensing and applied to forward scatter and meteorological polarimetric systems. After an overview of radar fundamentals to introduce the general terminology and concepts, results are presented at the end of each chapter. In this respect, a generalized electromagnetic model is first presented in order to predict the response of forward scatter radars (FSRs) for airtarget surveillance applications in both near-field and far-field regions. The model is discussed for increasing levels of complexity: a simplified near-field model, a near-field receiver model and a near-field receiver and transmitter model. FSR results have been evaluated in terms of the effects of different target electrical sizes and detection distances on the received signal, as well as the impact of the trajectory of the moving objects and compared with a customized implementation of a full-wave numerical tool. Secondly, a new data processing methodology, based on the statistical analysis of ground-clutter echoes and aimed at investigating the monitoring of the weather radar relative calibration, is presented. A preliminary study for an improvement of the ground-clutter calibration technique is formulated using as a permanent scatter analysis (PSA) and applied to real radar scenarios. The weather radar relative calibration has been applied to a dataset collected by a C-band weather radar in southern Italy and an evaluation with statistical score indexes has drawn through the comparison with a deterministic clutter map. The PSA technique has been proposed using a big metallic roof with a periodic mesh grid structure and having a hemispherical shape in the near-field of a polarimetric C-band radar and evaluated also with an ad-hoc numerical implementation of a full-wave solution. Finally, a radar-based snowfall intensity retrieval is investigated at centimeter and millimeter wavelengths (i.e., at X, Ka and W band) using a high-quality database of collocated ground-based precipitation measurements and radar multi-frequency observations. Coefficients for the multifrequency radar snowfall intensity retrieval are empirically derived using multivariate regression techniques and their interpretation is carried out by particle scattering simulations with soft-ice spheroids. For each topic, conclusions are proposed to highlight the goals of the whole work and pave the way for future studies

Forward scatter radar for air surveillance: Characterizing the target-receiver transition from far-field to near-field regions

A generalized electromagnetic model is presented in order to predict the response of forward scatter radar (FSR) systems for air-target surveillance applications in both far-field and near-field conditions. The relevant scattering problem is tackled by developing the Helmholtz-Kirchhoff formula and Babinet's principle to express the scattered and the total fields in typical FSR configurations. To fix the distinctive features of this class of problems, our approach is applied here to metallic targets with canonical rectangular shapes illuminated by a plane wave, but the model can straightforwardly be used to account for more general scenarios. By exploiting suitable approximations, a simple analytical formulation is derived allowing us to efficiently describe the characteristics of the FSR response for a target transitioning with respect to the receiver from far-field to near-field regions. The effects of different target electrical sizes and detection distances on the received signal, as well as the impact of the trajectory of the moving object, are evaluated and discussed. All of the results are shown in terms of quantities normalized to the wavelength and can be generalized to different configurations once the carrier frequency of the FSR system is set. The range of validity of the proposed closed-form approach has been checked by means of numerical analyses, involving comparisons also with a customized implementation of a full-wave commercial CAD tool. The outcomes of this study can pave the way for significant extensions on the applicability of the FSR technique

Electromagnetic modeling of forward scatter radar

The forward scattering (FS) phenomenon is investigated in this work referring to a typical radar scenario where a metallic target crosses the baseline while is illuminated by a transmitting source. A straightforward electromagnetic (EM) analytical model is provided to predict the received signal both in near- and farfield conditions. The effect of different distances between target and receiving antenna are analyzed in terms of scattered and total EM fields. The results have been validated through an ad-hoc numerical implementation of a full-wave solution. Physical insight into the FS effect and restrictions on the applicability of the EM model are also discusse

C-band polarimetric weather radar calibration using a fuzzy logic fusion of three techniques

The goal of this work is to show the possibility to combine three different calibration techniques to obtain a reliable monitoring of the radar system through the definition of a quality index concept. The fuzzy logic approach uses the idea to convert the calibration error in a so called linguistic variable defined as the impact of it on the parameter estimation. After an inference step, we obtain a quality matrix that represents the quality index of calibration on the observed variables in different part of the system (transmitting and receiving). This information can be extremely important for the remote monitoring and the realtime diagnosis of the radar system state. The output of the procedure is a diagnostic quality index, useful to establish where and when a technical intervention on the radar system is necessary. Results, using copolar and differential reflectivity, are shown for a C-band weather radar operating in Italy

Forward scatter radar modeling: Effects of near field for canonical targets

The forward scatter radar (FSR) operation is investigated in this work considering for the first time the significant effects on the signal detection related to the distances between target and Tx/Rx antennas. Referring to a typical FSR scenario (a movable target crossing the baseline), specific attention is paid to the characterization of the forward-scatter cross-section (FS-CS). Based on a suitable numerical evaluation of diffraction integrals as a function of target/receiver distance, the signal complex envelope has been derived not only in far-field conditions, but also in the near-field Fresnel region, for some reference scatterer shapes and related FS-CS. According to standard procedures, the overall FS amplitude and phase signature of typical conductive targets have been evaluated as a function of the parameters involved. The relevant results allow for a deeper analysis of the performance and criticalities of FSR in practical conditions

Analysis of canonical targets in near field for forward scatter radar applications

Near-field effects in Forward Scatter Radar (FSR) applications are analyzed, focusing the attention on the characterization of the received signal as a function of target/antenna distance and of target size. A simulated analysis of the forward-scatter cross-section (FS-CS) is carried out for a typical FSR scenario where a movable target crosses the baseline. In addition to the known far-field conditions, the results are presented also for the significant near-field Fresnel region, based on a suitable numerical evaluation of the diffraction integrals as a function of the geometrical and physical parameters involved. According to a basic modeling approach, the overall FS amplitude and phase signature of typical conductive targets have been evaluated in terms of their size and distance to the antennas. The above investigations allow not only for an accurate analysis of the forward scattering problem but also for a physical insight on the performance of the FSR in near-field conditions

Modeling the forward-scatter cross section of 3-dimensional objects by means of the shadow contour theorem: an assessment

In this contribution, we analyze the forward-scatter cross-section (FS-CS) of three-dimensional (3-D) metallic targets in a forward scatter radar (FSR) system, moving along arbitrary trajectories, in the transition between far- and near-field regions with respect to the receiving antenna. A vector formulation is introduced, together with a simplified approach based on a physical-optics solution of the scattering integral, and validated by means of full-wave numerical evaluations. This model is exploited to characterize the FS-CS of 3-D targets that have specific 2D contours and cross the baseline at variable distances and directions with respect to the receiving antenna. For these targets, the application of an extended Shadow Contour Theorem (SCT) provides an extremely simplified model that can be particularly useful for a fast and accurate characterization of the FS-CS, leading, in specific cases, to closed-form analytical formulation of the scattering. By comparing the FS-CS of the 3-D object having both sharp edges and smooth shapes with the results of the SCT applied to the 2-D shapes, an accurate assessment of the theorem is outlined. This provides useful insights on the application of the SCT in conjunction with a PO solution of the object contour, for developing advanced signal processing techniques based on a realistic but simplified FS-CS target

Analytical modeling and numerical validation of forward scattering for radar applications

The forward scattering phenomenology is investigated in this work, providing a straightforward electromagnetic analytical model valid also in near-field conditions. A typical configuration useful for forward scatter radar operational scenarios, where a metallic object is illuminated while crossing a baseline, is considered. The effects of different target sizes on the scattered signal are evaluated and discussed. A full-wave numerical solution is also developed through the implementation with a commercial tool to validate the proposed analytical formulation