Adaptive detection of fast moving targets by means of high range resolution radar is considered. It is assumed that a fast-moving target of interest has a few range cells migration during the coherent processing interval and the clutter power fluctuates rapidly along the range. Therefore, the target competes with the clutter responses in a few adjacent range cells, modeled by Compound-Gaussian process. The adaptive CFAR detector of range-migrating targets is designed and it is complemented by the algorithm for covariance matrix estimation from the reference data. The generalized approach for detection of range-extended migrating targets is provided. The performance of the proposed detectors is evaluated via numerical simulations, showing valuable improvement over the conventional techniques. ... Read more

The problem considered is that of estimating unambiguously migrating targets observed with a wideband radar. We extend a previously described sparse Bayesian algorithm to the presence of diffuse clutter and off-grid targets. A hybrid-Gibbs sampler is formulated to jointly estimate the sparse target amplitude vector, the grid mismatch, and the (assumed) autoregressive noise. Results on synthetic and fully experimental data show that targets can be actually unambiguously estimated even if located in blind speeds. ... Read more

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. ... Read more

When designing a new radar system, standard resolution trade-offs play a major role, providing the basic parameters of the radar, such as size, update rate, and range. Besides, diversity has long been used for mitigating fading effects due to the fluctuation of targets and clutter. However, with the arrival of more flexible systems, using multiple parallel channels on transmit and receive, and wider instantaneous bandwidths, these standard trade-offs are becoming less simple—and more flexible. In this communication, we will analyse the benefits of diversity and its relations with range, Doppler, and angle, for detection and location of moving targets with wideband/wide-beam radar systems. The idea is to contribute to a better understanding of the real benefits of agile transmissions for detection/localization of moving targets, focusing on range, velocity, and angular measurement improvements, as well as on the benefits for detection of moving targets. Special attention will be given to the quality of the different wideband wide-beam sensor modes for long-range surveillance, and new results on detection of moving targets in clutter will be provided to demonstrate the effectiveness of these new architectures for small target detection at long range, in difficult environments.
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This paper deals with the problem of coherent radar detection of fast moving targets in a high range resolution mode. In particular, we are focusing on the spiky clutter modeled as a compound Gaussian process with rapidly varying power along range. Additionally, a fast moving target of interest has a few range cells migration within the coherent processing interval. Two coherent CFAR detectors are proposed taking into account target migration and highly inhomogeneous clutter. Both detectors involve solution of a transcendental equation, carried out numerically in a few iterations. The performance evaluation is addressed by numerical simulations and it shows a significant improvement in detection of fast moving targets in inhomogeneous heavy tailed radar clutter. ... Read more

To improve the efficiency of surveillance radars, we describe a method using a single train of wideband (≈10% relative bandwidth) coherent pulses, rather
than a sequence of several trains of narrow-band pulses. In this technique, target velocity is measured by both pulse-topulse (ambiguous modulo 2π) phase rotation and target distance variation (distance migration) along the pulse train.
The modeling of the targets and clutter are first described, then the limitations of the matched filter processing (existence of residual ambiguities in the form of secondary lobes) are highlighted. An iterative adaptive approach makes it
possible to remedy these faults, in simulation as well as on real experimental signals.
Adaptive clutter suppression techniques are then examined: the influence of the echo spectrum spread and the influence of the bandwidth parameter are analyzed in detail, and an adaptive detector is developed, combining the elimination of clutter and the detection decision.
In conclusion, the operational benefits of this detection by a single train of wideband pulses, compared to the usual technique combining a sequence of narrow-band pulse trains, are summarized, both in terms of sensitivity gains and in terms of velocity resolution and target analysis capability. ... Read more

Pulse-Doppler radars classically transmit a train of pulses with a narrow bandwidth at a constant pulse repetition frequency (PRF) to detect moving targets. By design, they are subject to the well-known problem of range and/or velocity ambiguities. Indeed, the ambiguous velocity v a and range ambiguity R a are linked through ... Read more

The problem of range-migrating target detection in a compound-Gaussian clutter is studied here. We assume a target to have a range-walk of a few range cells during the coherent processing interval, when observed by wideband radar with high range resolution. Two CFAR detectors are proposed assuming different correlation properties of clutter over range. The detectors' performance is studied via numerical simulations and a significant improvement over existing techniques is demonstrated. ... Read more

This study presents a simple yet ingenious transmit diversity technique (so-called hybrid codes) for phased array radar. Its main property is the capability of digital beamforming on transmit just like with a set of orthogonal signals employed by coherent multiple-input–multiple-output radar and simplicity (only one waveform has to be generated in time). The performance of the hybrid codes is examined by analysing the transmit ambiguity functions containing beampatterns and range profile for all angular directions of interest. ... Read more

In this paper the problem of unambiguous moving target detection using wideband radar is considered. Doppler ambiguities, which are present in the low pulse repetition frequency mode, are transformed into ambiguous sidelobes of targets and clutter using range migration effect. However, the level of these sidelobes is typically high, such that standard detectors suffer from false alarms generated by the ambiguous sidelobes of real targets. To remove these false alarms two new detectors assuming Gaussian distribution of clutter and exploiting high resolution spectral estimation are developed. These detectors are based on spectral estimation obtained with non-parametric Iterative Adaptive Approach from spectrum analysis and satisfy bounded false alarm condition. Approach to reduce the number of reference cells for covariance matrix estimation is discussed. The benefits of the proposed detectors are demonstrated via numerical simulations showing improvement over existing algorithms. ... Read more

In this paper the influence of clutter power spectrum on unambiguous radar target detection with single low pulse repetition frequency wideband waveform is analyzed. Impact of both stationary and diffuse clutter components for different signal bandwidths and coherent processing intervals (CPI) is studied. Exponential model of the ground clutter power spectrum for the diffuse component is used. For the first time, radar detection performance for wideband signals at ambiguous to clutter velocities is predicted as function of bandwidth and CPI. ... Read more

In this paper, we consider the problem of estimating a signal of interest embedded in noise using a sparse signal representation (SSR) approach. This problem is relevant in many radar applications. In particular, estimating a radar scene consisting of targets with wide amplitude range can be challenging since the sidelobes of a strong target can disrupt the estimation of a weak one. Within a Bayesian framework, we present a new sparse-promoting prior designed to estimate this specific type of radar scene. The main strength of this new prior lies in its mixed-type structure which decorrelates sparsity level and target power, as well as in its subdivided support which enables the estimation process to span the whole target power range. This algorithm is implemented through a Monte-Carlo Markov chain. It is successfully evaluated on synthetic and semiexperimental radar data and compared to state-of-the-art algorithms. ... Read more

Within the scope of sparse signal representation, we consider the problem of velocity ambiguity mitigation for wideband radar signal. We present a Bayesian robust algorithm based on a new sparsifying dictionary suited for range-migrating targets possibly straddling range-velocity bins. Numerical simulations
on experimental data demonstrate the ability of the proposed algorithm in mitigating velocity ambiguity. ... Read more

One of the most striking challenges that radar designers have to deal with, when developing new doppler systems, is to overcome the difficulty of working with ambiguous velocities. Even using high PRF’s, target’s velocities become ambiguous because wavelengths are getting shorter. This article tries to depict an idea of becoming unambiguous in doppler, using only one PRF and without range tracking, taking advantage of target’s range migration if high range resolution radars are used. Simulations will be shown justifying the idea, but also, pointing out some limitations depending on the radar’s operational parameters and target’s relative motion. ... Read more

A radar scatterometer operates by transmitting a pulse of microwave energy toward the ocean’s surface and measuring the normalized (per-unit-surface) radar backscatter coefficient (r8). The primary application of scatterometry is the measurement of near-surface ocean winds. By combining r 8 measurements from different azimuth angles, the 10 m vector wind can be determined through a Geophys- ical Model Function (GMF), which relates wind and backscatter. This paper proposes a mission concept for the measurement of both oceanic winds and surface currents, which makes full use of earlier C-band radar remote sensing experience. For the determination of ocean currents, in particular, the novel idea of using two chirps of opposite slope is introduced. The fundamental processing steps required to retrieve surface currents are given together with their associated accuracies. A detailed description of the mission proposal and comparisons between real and retrieved surface currents are presented. The proposed ocean Doppler scatterometer can be used to generate global surface ocean current maps with accuracies better than 0.2 m/s at a spatial resolution better than 25 km (i.e., 12.5 km spatial sampling) on a daily basis. These maps will allow gaining some insights on the upper ocean mesoscale dynamics. The work lies at a frontier, given that the present inability to measure ocean currents from space in a consistent and synoptic manner repre- sents one of the greatest weaknesses in ocean remote sensing. ... Read more