M. Ash

Determination of Sweep Linearity Requirements in FMCW Radar Systems Based on Simple Voltage-Controlled Oscillator Sources

Linear frequency modulated (FM), or chirp, pulse compression is a widely used technique for improving the range resolution of radar systems, although it often places quite stringent demands on FM sweep linearity. This paper examines the impact of sweep nonlinearities on the performance of frequency modulated continuous wave (FMCW) radar systems, particularly those employing simple voltage-controlled oscillator (VCO) sources, using a new and straightforward approach based on the fractional slope variation (FSV). Modeled results are presented, assuming a square-law source nonlinearity representation, showing the effect of such nonlinearities on point-target response and range resolution. These results are then related to the standard definition of linearity. Measurements from a commercial VCO are finally used to convincingly validate the work, resulting in a simple and practical method to predict the impact of source nonlinearity, as defined by the FSV parameter, on the performance of an FMCW radar system.

FMCW radar imaging of avalanche-like snow movements

High quality field measurements of avalanche flows are required for calibrating computational models which are an essential tool in managing the threat posed by these flows. In this paper we present a new C-band FMCW radar system developed at University College London for gathering highresolution avalanche flow data. The radar employs a full deramp hardware architecture, a diverse set of frequency ramps, and an 8-channel receiver array. We also show initial results of a small-scale field trial carried out using a single channel prototype radar deployed in a snow chute. The results are presented as range-time plots. A simple calculation of the expected flow velocity due to gravity agrees with the estimated experimental value. The results demonstrate the capability of the radar system to record high range resolution microwave images of snow movements. The experiments reported here were carried out as a precursor to full trials of the radar system during which images of full scale avalanche flows will be captured.

The dynamics of surges in the 3 February 2015 avalanches in Vallée de la Sionne.

Five avalanches were artificially released at the Vallee de la Sionne test site in the west of Switzerland on 3 February 2015 and recorded by the GEOphysical flow dynamics using pulsed Doppler radAR Mark 3 radar system. The radar beam penetrates the dilute powder cloud and measures reflections from the underlying denser avalanche features allowing the tracking of the flow at 111 Hz with 0.75 m downslope resolution. The data show that the avalanches contain many internal surges. The large or “major” surges originate from the secondary release of slabs. These slabs can each contain more mass than the initial release, and thus can greatly affect the flow dynamics, by unevenly distributing the mass. The small or “minor” surges appear to be a roll wave-like instability, and these can greatly influence the front dynamics as they can repeatedly overtake the leading edge. We analyzed the friction acting on the fronts of minor surges using a Voellmy-like, simple one-dimensional model with frictional resistance and velocity-squared drag. This model fits the data of the overall velocity, but it cannot capture the dynamics and especially the slowing of the minor surges, which requires dramatically varying effective friction. Our findings suggest that current avalanche models based on Voellmy-like friction laws do not accurately describe the physics of the intermittent frontal region of large mixed avalanches. We suggest that these data can only be explained by changes in the snow surface, such as the entrainment of the upper snow layers and the smoothing by earlier flow fronts.

A New Multistatic FMCW Radar Architecture by Over-the-Air Deramping

Frequency modulated continuous wave (FMCW) radar is widely adopted solution for low-cost, short to medium range sensing applications. However, a multistatic FMCW architecture suitable for meeting the low-cost requirement has yet to be developed. This paper introduces a new FMCW radar architecture that implements a novel technique of synchronizing nodes in a multistatic system, known as over-the-air deramping (OTAD). The architecture uses a dual-frequency design to simultaneously broadcast an FMCW waveform on a lower frequency channel directly to a receiver as a reference synchronization signal, and a higher frequency channel to illuminate the measurement scene. The target echo is deramped in hardware with the synchronization signal. OTAD allows for low-cost multistatic systems with fine range-resolution, and low peak power and sampling rate requirements. Furthermore, the approach avoids problems with direct signal interference. OTAD is shown to be a compelling solution for low-cost multistatic radar systems through the experimental measurements using a newly developed OTAD radar system.

Improving the sensitivity and phased array response of FMCW radar for imaging avalanches

Radar has proved to be a valuable tool for gathering velocity measurements of flowing avalanches. Geodar, a recently developed FMCW, phased array radar, successfully improved upon existing avalanche radar measurements and has to date provided the community with high-quality avalanche measurements over several winter seasons. Indeed, Geodar has recorded measurements of flowing avalanches in two-spatial dimensions for the first time. Following the success of Geodar, the authors are now redesigning the system to improve its performance in terms of sensitivity and array response. This paper summarises the issues encountered with the original design and describes how these issues have been addressed with the new design. This includes a drastic change to the receiver design, shifting the deramp processing onto the antenna board, and printing the antenna array and its associated RF receiver circuitry on a single PCB. The design is shown to dramatically improve the array sidelobe performance, and enhance the sensitivity of the receiver by reducing the transmission line losses in the RF chain.

Autonomous phase-sensitive radio echo sounder for monitoring and imaging antarctic ice shelves

A low-power, autonomous phase-sensitive radio-echo sounder (ApRES) radar system has been developed at University College London, in collaboration with the British Antarctic Survey, for monitoring and imaging Antarctic ice shelves. The system is ground-based and uses a direct digital synthesizer to implement a frequency modulated continuous wave radar architecture. The system operates between 200 MHz to 400 MHz with a dc power consumption of 4.8 W. Since January 2014, three ApRES systems have been deployed on the ice shelf of Pine Island Glacier, West Antarctica. One system is configured in monostatic point ranging mode, while two systems are configured in an orthogonal 8×8 multiple input multiple output (MIMO) arrangement that enables two-dimensional through ice imaging.

Phased array antenna for avalanche FMCW radar

In this work, design and analysis of a single element of a 16-element phased array antenna is presented. By means of sub-arraying and overlapping techniques, the required ±14.5° azimuth and ±22.5° elevation angles were achieved while 200 MHz bandwidth and 13.7 dBi gain were obtained.

Preliminary antenna system design for FMCW avalanche radar

This paper described the design and construction of a preliminary microstrip array antenna at 5.3 GHz. The antenna is going to be applied to an FMCW avalanche radar. The antenna design which composed of an array of 4 × 2 patches could achieve the high gain of 15.6 dB with a wideband of 90%. The high gain and wideband attributes is also achieved by separating the feed network from the main patches and increasing the antenna height. In order to ensure the power is transferred smoothly from the main input port, the feed network is designed in a nover spider-like tapered feed while ensuring the antenna performance is not affected.

Through Wall Radar Classification of Human Micro-Doppler Using Singular Value Decomposition Analysis

The ability to detect the presence as well as classify the activities of individuals behind visually obscuring structures is of significant benefit to police, security and emergency services in many situations. This paper presents the analysis from a series of experimental results generated using a through-the-wall (TTW) Frequency Modulated Continuous Wave (FMCW) C-Band radar system named Soprano. The objective of this analysis was to classify whether an individual was carrying an item in both hands or not using micro-Doppler information from a FMCW sensor. The radar was deployed at a standoff distance, of approximately 0.5 m, outside a residential building and used to detect multiple people walking within a room. Through the application of digital filtering, it was shown that significant suppression of the primary wall reflection is possible, significantly enhancing the target signal to clutter ratio. Singular Value Decomposition (SVD) signal processing techniques were then applied to the micro-Doppler signatures from different individuals. Features from the SVD information have been used to classify whether the person was carrying an item or walking free handed. Excellent performance of the classifier was achieved in this challenging scenario with accuracies up to 94%, suggesting that future through wall radar sensors may have the ability to reliably recognize many different types of activities in TTW scenarios using these techniques.