Waddah A. Al-Ashwal

Analysis of bistatic sea clutter - Part II: Amplitude statistics

The amplitude statistics of simultaneously recorded bistatic and monostatic sea clutter are analyzed and fitted to five different commonly used distributions to model sea clutter. We find that under the measurement conditions the bistatic geometry reduced the effect of specular spikes but not those due to the modulation. It was found that the bistatic geometry could offer significant advantages in detection particularly at horizontal polarization and close to a bistatic angle of 90°.

Evaluation of coherent netted radar carrier stability while synchronised with GPS-disciplined oscillators

In this paper the dual-mixer time delay (DMTD) technique is used to characterize netted radar carrier stability. Moreover, the performance of synchronization via twisted-pair (TP) cable was compared to that of GPS-disciplined oscillators (GPSDO). This was done using an experimental coherent netted radar (NetRAD), developed at University College London (UCL), UK, and quartz-based GPSDOs, developed at the University of Cape Town (UCT), South Africa. NetRAD was configured as a DMTD test bench, using the existing radar hardware. Parameters such as time and frequency offset, time deviation and Allan deviation were extracted through post-processing of the sampled IF signal. Zero-range measurements conducted under laboratory conditions are presented alongside field measurements conducted over a base-line of 100 metres. Performance of the UCT GPSDOs and the reference TP cable systems were comparable in terms of frequency stability and phase jitter. However, as was expected, the GPSDO time sync was much less precise.

Analysis of bistatic sea clutter - Part I: Average reflectivity

Based on two low grazing angle simultaneously recorded out-of-plane bistatic and monostatic S-band sea clutter datasets, and covering bistatic angles from 30°-120°, we analyze the average normalized radar cross section (σ°), and show that under the measurement conditions the ratio between σ_B° and σ_M° tends to a minimum around a bistatic angle of 90°, particularly at horizontal polarization. However, the cross-polarized σ° was larger for the bistatic clutter at bistatic angles close to 90°.

Multistatic networked radar for sea clutter measurements

NetRad, consisting of three fully coherent S-Band (2400 MHz) nodes, synchronised by clock and trigger cables, or, GPS Disciplined Oscillators (GPSDOs) with a programmable trigger, has been underdevelopment at UCL and UCT for a number of years. Basic output power is low (200 mW), but a high power transmitter (500W peak) is available for one node. The cable links limit bistatic baselines to some 100m but the GPS Oscillator option allows for full multistatic operation, including forward scatter. The nodes are tied together by means of a wireless network (5 GHz) and command and control software, which allows the radars to be triggered remotely via the GPSDOs, and the data capture parameters of the nodes to be altered at will. Sensible results on small targets out to 2 km are possible, longer for large targets. We show measurements from trials on sea clutter and moving targets, in the south of the UK and near Simons Town, South Africa.

Sea Clutter Mitigation Using Resonance-Based Signal Decomposition

A sea clutter mitigation method based on sparse optimization is proposed and tested with real radar data collected using a 2.425-GHz netted radar system developed at University College London, London, U.K. The proposed method was able to separate the target returns from the sea clutter returns, thus increasing the signal-to-interference ratio. It is shown that the extracted signal had a lower false alarm rate compared to the original signal.

Measurements of bistatic radar sea clutter

Bistatic radar is a technique of considerable potential importance and interest. Despite this, current understanding of the properties of bistatic clutter, and in particular, bistatic sea clutter, is limited at best. We present some results of a recent trials campaign to gather bistatic sea clutter data, and to analyse the data in order to develop models to represent bistatic radar sea clutter. The results indicate that the shape parameter of the compound K distribution model fitted to the data tends to be higher for the bistatic clutter than for the equivalent monostatic clutter. This suggests that a bistatic geometry may allow a lower detection threshold for a given probability of false alarm, and hence give improved detection performance of weak targets against a clutter background compared to the conventional monostatic geometry.

NetRAD multistatic sea clutter database

This paper describes a multistatic, sea clutter and vessel database, assembled using the three node, S Band radar, known as NetRAD (for, “Netted Radar”). This data was collected in the United Kingdom and South Africa during 2009-201. It is the intention of the investigators and sponsors of this work to make the raw data available to individuals and organisations interested in processing this multistatic data in support of the development of the understanding of sea clutter and vessel properties in the multistatic configuration.

Comparison between measurement and simulation of monostatic and bistatic sea clutter

There has been considerable research into analytical modeling of bistatic sea clutter However, such models have generally not been validated against measured data. A comparison between low grazing angle simultaneously recorded out-of-plane bistatic and monostatic S-band sea clutter and electromagnetic simulation is presented in this paper. Both vertical and horizontal polarizations were recorded and the bistatic angle was varied from 60° - 120°. The simulation results were in agreement with the measurement in the monostatic geometry and there were significant differences in the bistatic geometry.

Simplified Three-Cornered-Hat Technique for Frequency Stability Measurements

We propose a novel technique allowing the use of the three-cornered-hat method with two devices under test (DUTs) and a time-tagging system that employs a common reference oscillator. The precision of a time-tagging system is reduced by fluctuations in the timebase, which are canceled when the relative phase between the two DUTs is measured. However, the raw time-tags in this system provide a phase comparison between the DUTs and the system timebase, allowing the use of the three-cornered hat with some dual-channel measurement instruments.

Preliminary analysis of monostatic and bistatic Doppler signature of small maritime target

The simultaneous bistatic and monostatic Doppler signatures of a small boat are measured and analyzed. The data was recorded using the UCL NetRAD 2.4 GHz netted radar system. Two datasets are presented: one at small bistatic angle (~ 4°) and the other at a larger angle (~ 91°). There was little difference between the monostatic and bistatic channels in the former, while there were significant differences in the latter. In addition, by using detections from both channels the true velocity of the target is estimated.