Alan Langman

Development of a low cost SFCW ground penetrating radar

Due to their system complexity and high component cost, stepped frequency continuous wave radars have not been popular in the ground penetrating radar industry. However, over the last decade the cost of RF technologies has decreased considerably, making it more feasible to make SFCW GPRs. This paper discusses the implementation and development of a low cost SFCW GPR using digital radio technology, a homodyne single channel receiver and a digital signal processor. The radar operates over a bandwidth from 490 MHz to 780 MHz and is capable of taking a single depth profile measurement using 256 frequency steps in less than 0.5 seconds. The results of field trials are also presented.

Growing horns: Applying the Rhino software defined radio system to radar

Rhino is a hardware and software tool flow designed for software defined radio applications. We show that Rhino can be used for rapid prototyping of radar hardware systems, with minimal adjustments to the core Rhino system, with the new tool set being called, Rhinoradar. The radar user is able to specify desired radar configurations (waveforms, repetition rates, sampling schemes, matched filtering) via simple GNURadio-like processing blocks. The radar user is thus largely screened from complex Hardware Description Language (HDL) coding. The Rhino hardware provides two FMC interfaces, giving access to a wide range of commercial A/D and D/A boards. It also supports the IEEE 1558 network timing standard, allowing multiple boards to be synchronised via an Ethernet Network. Dual 10 gigabit network interfaces allow for real time data streaming for recording or further signal processing.

Hardware cancellation of the direct coupling in a stepped CW ground penetrating radar

A stepped CW ground penetrating radar using UHF frequencies is being developed by the University of Cape Town. One of the major problems encountered is a large direct coupling between the transmit and receive antennas. This coupling limits the dynamic range of the system by inserting a large signal into the receiver. The hardware implementation of a digitally controlled RF cancellation circuit is discussed. This RF system comprises of an analogue bi-phase modulator used as a wideband phase-shifter and a PIN diode attenuator. This system, controlled by a PC, was attached to the front end of the SFCW radar. Results of the cancellation circuit used to cancel a cable over a 200 MHz bandwidth and a coupling vector are presented.<<ETX>>

The RHINO platform: charging towards innovation and skills development in software defined radio

This paper presents a pilot study on the development of a reconfigurable computing platform for use in prototyping Software Defined Radio (SDR) applications and building technical knowledge in this specialist area. SDR is becoming an increasingly popular approach for building experimental radio and radar systems, giving researchers significant flexibility in choosing bandwidths, modulation and other operational parameters traditionally fixed by front-end hardware. The SDR approach involves constructing and testing radio applications on reusable platforms, thereby reducing costs and time spent changing physical layer hardware. This paper discusses use of the Reconfigurable Hardware Interface for comptiNg and radiO (RHINO) platform as a hardware platform for novice engineers to develop SDR skills and to prototype radio systems.

Drill head mounted obstacle avoidance radar

Horizontal drilling in soft soil provides an efficient and cost effective solution for the installation of utilities. However, with the increased congestion of underground utilities, the probability of damaging mislocated or unknown utilities increases, reducing the financial benefits of this technology and increasing the possibility catastrophic damage such as striking gas lines. It is hence important to develop instrumentation that is capable of locating obstacles lying along the bore paths. This paper discusses the development of a obstacle avoidance system based on ground penetrating radar technology. The system is a stepped frequency continuous wave (SFCW) radar that has been designed to fit within a standard 2.75 inch diameter drill head. The only above-ground components are the human machine interface (HMI) and power supply. Communication and power are transmitted underground via a wireline technique. An advanced demonstration model has been built and tested. The paper provides an overview of the requirements of an obstacle avoidance radar system. This is followed by a brief discussion of radar and antenna development required to implement the system. Finally results of indoor and outdoor field trials will be provided.

Improving the resolution of a stepped frequency cw ground-penetrating radar

One of the major problems in sub-surface radar is the compromise between resolution and penetration depth. Stepped frequency continuous wave radars (SFCW) have improved the penetration depth of sub-surface radars by achieving greater sensitivity, instantaneous dynamic range, and better spectral control than conventional pulsed systems. However, the resolution in SFCW radar systems is limited by the fast Fourier transform (FFT) processing required to extract depth (i.e., range) information from the vector frequency data. This paper investigates the potential use of the extended prony method for range extraction in a SFCW ground penetrating radar (GPR). This method fits data to a complex exponential model, without placing the restriction on the data that the targets are constrained to definite range bins. This allows for the resolution of the system to go beyond the limitations set by the bandwidth of the waveform. Simulations are presented to examine the effects of the signal-to-noise ratio (SNR) on performance, when applying the extended prony method to a simple GPR model. At all times the results are compared with the standard FFT processing. A prototype radar system has been constructed at the University of Cape Town using standard laboratory equipment, a computer and additional digital and rf circuitry. The antennas used are two ridged wideband horns. Targets were buried in a sandpit and measurements were taken over a 2 GHz bandwidth with a center frequency of 3 GHz. Comparisons ware made between the FFT and the extended prony method for different portions of the system bandwidth, showing the extended prony method can achieve high resolution using a reduced bandwidth.

Polarimetric model for a stepped-frequency continuous-wave ground-penetrating radar

Polarimetric measurements provide additional information to aid in determining the geometric and physical properties of sub-surface targets. In this paper algorithms are derived to extract polarimetric target descriptors from a Stepped Frequency Continuous Wave Ground Penetrating Radar (SFCW GPR) data. The algorithm uses the multi-snapshot Matrix Pencil-of-function Method, to estimate the parameters of a fully polarimatric SFCW GPR model developed in this paper. The processing is applied to both simulated and laboratory measurements, and the results demonstrate the validity of this technique.

Dynamically configurable GPR data acquisition and display application

ABSTRACT The GPR data acquisition software is arguably one of the most important components of a Ground Penetrating Radar system. This software needs to ensure the capture of reliable and repeatable data by a diverse user community. Yet, too many commercial and academic systems provide a single- user highly configurable interface for all applications. This paper describes the development of a configurable data acquisition and display application for use with ground penetrating radar. It is proposed that the standard GUI-based application that offers access to all controls and settings is distracting to many GPR end-users. It is therefore suggested that an application should present only the necessary controls to the end-user, and all other options should be inaccessible. This paper describes the development of such an application from a user requirements analysis to the design and implementation of an object-oriented, Java-based solution.

The use of polarimetry in subsurface radar

Extraction of target information from the measurement of the state of polarization of the scattered wave has been a promising area of research for a number of years. This paper discusses the theory and implementation of a stepped frequency CW polarimetric subsurface radar. The extended Prony method is used to obtain high resolution range profiles from which the scattering matrices are extracted. The results of laboratory trials are presented. These include measurements of the scattering matrix for a pipe and plate conducting targets, buried in a large sand box. Polarization responses for these targets are plotted to emphasize the use of the scattering matrix for target discrimination.<<ETX>>

Assessment of a digital quadrature demodulator for a stepped frequency radar

A direct digital demodulator for a stepped frequency radar was modeled and its performance estimated by computer simulation. The performance of a prototype was evaluated. Timing jitter was found to be the most significant cause of error in both cases.