Wideband radars have been proposed for detection of moving targets, with unique capability of non-ambiguous detection due to range migration. Moreover, frequency diversity has long been used for mitigating the fading effects caused by target and clutter fluctuations. The real benefits of wideband radars are difficult to analyze, since they derive from the combined effects of target resolution in range, migration over successive cells of clutter, Doppler resolution and instantaneous bandwidth, and residual ambiguities in Doppler. In order to contribute to a better understanding of the benefits of agile transmissions for detection of moving targets, clutter cancelling performances of wideband radars are examined, demonstrating clear benefits from diversity on clutter and target, primarily – but not only – obtained through target migration effects. Special attention is given to long-range surveillance and tracking, and new results on detection of moving targets in clutter will be provided to demonstrate the effectiveness of these new architectures for small targets detection at long range, in difficult environments. Finally, recommendations for system designs that improve the discrimination of moving targets against fixed and diffuse clutter are presented.

This paper proposes two bias correction methods for the practical planar polarimetric phased array weather radar, namely, the boresight correction and the array pattern-based correction. As an extension of the projection matrix method developed in previous research, the performance of the boresight correction considering the measurement errors of element patterns and the impacts of entire array patterns on polarimetric variables is theoretically evaluated. It is shown that the measurement errors of element patterns are crucial for the polarimetric bias correction. Furthermore, for a planar electronically scanned antenna, the measurement performance of the linear depolarization ratio varies in the beam direction, while the measurement performance of the differential reflectivity remains almost the same within the beam scan area. In order to compensate the impacts of entire array patterns on polarimetric variables, the array pattern-based correction method is formulated, and its performance is theoretically analyzed. Assessments of the analysis and future research are discussed.

The present paper proposes an innovative mission concept for a C-band fan-beam wind scatterometer with both ocean wind vector and ocean current vector measurement capability on a global scale.

Due to the contradiction between the high sensitivity requirement and low transmission power of weather radars with solid-state transmitters, a pulse compression technique is necessary. For the purpose of range sidelobe suppression, methods based on amplitude modulation and a mismatched filter are commonly used for target detection radars, which are not applicable for weather observations because of its drawbacks such as main lobe expansion and power loss. This letter presents a nonlinear frequency modulation pulse compression waveform to achieve a very low range sidelobe level. A mathematical model for waveform design is established, in which the time-frequency relation is expressed as the combination of a linear function and a sine series. Thus, a set of parameters can fully characterize the time-frequency curve. By using a simulated annealing algorithm, the optimal parameter set can be obtained, which shows that a peak sidelobe level under -60 dB is achievable. Finally, this kind of waveform is implemented on hardware, and its performance is verified.

This paper investigates the potential of cross polarization (VH) to extend the upper dynamic range of the wind measurements from ocean scatterometry. An analytical model for the VH polar scattering of the microwave radiation from ocean is proposed. The model combines the second-order small-slope approximation theory with the vector radiative transfer theory to obtain a statistical expression of the ocean scattering in presence of foam. Cross-polarized backscatter signals from RADARSAT-2 C-band synthetic aperture radar imagery, which were acquired during severe weather events, and collocated/time-coincident stepped-frequency microwave radiometer wind measurements by the National Oceanic and Atmospheric Administration's hurricane-hunter aircraft are used to verify the model. The validity of the model has been also proven against European Centre for Medium-Range Weather Forecasts forecasted winds. The results suggest that the present scattering model can be a valuable tool for understanding VH at very high wind speeds and for interpreting the data collected by the future dual polarimetric wind scatterometer (SCA), which will be flown on the Second Generation Meteorological Operational satellite program (MetOp-SG) as an evolution of the Advanced Scatterometer instrument on board MetOp.

The growing interest in achieving a better understanding of the physics that governs the cross-polar scattering of microwave radiation from ocean is triggered by recent measurement campaigns over hurricanes performed by NOAA Hurricane-Hunter winds and RADARSAT-2 [1]. From this data set the cross-polarized signals showed no evident loss of sensitivity as the wind-speed increased from 20 m/s up to 45 m/s. On the contrary C-band co-polar backscatter suffered from problems of incidence and azimuth angle-dependent signal saturations and dampening which makes it weakly sensitive above 25 m/s. On the basis of these considerations there are good reasons to think that the cross-polarized data can be a valuable tool for the retrieval of strong-to-severe wind speeds for future scatterometers. In this paper we present a physical scattering model based on the Small Slope Approximation theory [2] in conjunction with the Vector Radiative Transfer Theory [3] to describe the behavior of cross-polar scattering from ocean as function of the wind-speed and direction. Numerical results will be compared with real data from RADARSAT-2 and the brand new empirical Geophysical Model Function GMF-VH [1].

In this paper, we present a survey of some of the most common analytical approximate models that are used to describe the microwave sea surface scattering. The main strengths and weaknesses of the various methods are identified and critically discussed. Such models combine an adequate sea surface description with advanced electromagnetic theories to simulate both monostatic and bistatic scattering for a wide range of wind speeds, radar frequencies, incidence angles, different polarizations and arbitrary radar look direction with respect to the wind direction. Theoretical calculations for co-polar signals in C-band and Ku-band are in good overall agreement with the experimental data represented by the empirical models, CMOD5 and NSCAT, with the exception of HH-polarization at high incidence angles (above 40°). A parametric analysis on the sea surface spectrum, will demonstrate that the discrepancy between the measured and the simulated HH normalized radar cross-sections, is only in part due to the inefficiency of the spectrum and mostly due to additional scattering contribution from breaking waves, not taken into account by the most common analytical scattering theories.