Graham Brooker

Mutual Interference of Millimeter-Wave Radar Systems

This paper examines the probability that any millimeter-wave radar systems will interfere mutually by considering spatial, temporal, and operational frequency-related overlaps. It examines the nature and magnitude of the interference under different conditions and for different sensor types before concluding that in an overlapping frequency band, the probability that interference will occur is high. It goes on to demonstrate that, though there are some forms of interference that can be identified and controlled, there are others which are impossible to isolate, resulting in degraded target detection performance and tracking

Seeing through dust and water vapor: Millimeter wave radar sensors for mining applications

This paper defines the issues required for the development of successful visualization sensors for use in open cut and underground mines. It examines the mine environment and considers both the reflectivity of the rock and attenuation effects of dust and water droplets. Millimeter wave technology, as an alternative to the more commonly used laser and sonar implementations, is selected due to its superior penetration through adverse atmospheric conditions. Of the available radar techniques, frequency modulated continuous wave (FMCW) is selected as being the most robust. The theoretical performance of a number of 77 and 94 GHz FMCW millimeter wave radar systems is determined and these confirm the capability of these sensors in the mining environment. Implementations of FMCW radar sensors for simple ranging and three-dimensional surface profiling are discussed before data obtained during field trials in mines is presented to justify the selection of this technology. (c) 2007 Wiley Periodicals, Inc.

Radar-based perception for autonomous outdoor vehicles

Autonomous vehicle operations in outdoor environments challenge robotic perception. Construction, mining, agriculture, and planetary exploration environments are examples in which the presence of dust, fog, rain, changing illumination due to low sun angles, and lack of contrast can dramatically degrade conventional stereo and laser sensing. Nonetheless, environment perception can still succeed under compromised visibility through the use of a millimeter-wave radar. Radar also allows for multiple object detection within a single beam, whereas other range sensors are limited to one target return per emission. However, radar has shortcomings as well, such as a large footprint, specularity effects, and limited range resolution, all of which may result in poor environment survey or difficulty in interpretation. This paper presents a novel method for ground segmentation using a millimeter-wave radar mounted on a ground vehicle. Issues relevant to short-range perception in an outdoor environment are described along with field experiments and a quantitative comparison to laser data. The ability to classify the ground is successfully demonstrated in clear and low-visibility conditions, and significant improvement in range accuracy is shown. Finally, conclusions are drawn on the utility of millimeter-wave radar as a robotic sensor for persistent and accurate perception in natural scenarios.

Development and application of millimeter wave radar sensors for underground mining

This paper defines the issues that are required for the development of a successful underground range measurement sensor. It considers various options, including laser and sonar implementations, before focusing on a millimeter-wave frequency modulated continuous wave radar. The implementations of radar sensors for simple ranging and three-dimensional cavity profiling are then discussed before some data obtained in underground mines is presented to verify the radar performance through thick dust and vapor.

Reactive Collision Avoidance for Unmanned Aerial Vehicles Using Doppler Radar

Research into reactive collision avoidance for unmanned aerial vehicles has been conducted on unmanned terrestrial and mini aerial vehicles utilising active Doppler radar obstacle detection sensors. Flight tests conducted by flying a mini UAV at an obstacle have confirmed that a simple reactive collision avoidance algorithm enables aerial vehicles to autonomously avoid obstacles. This builds upon simulation work and results obtained using a terrestrial vehicle that had already confirmed that active sensors and a reactive collision avoidance algorithm are able to successfully find a collision free path through an obstacle field.

Decentralised ground target tracking with heterogeneous sensing nodes on multiple UAVs

This paper presents real time results of a decentralised air-borne data fusion system tracking multiple ground based targets. These target estimates are then used to construct a map of the environment. A decentralised communication strategy is employed which is robust to communication latencies and dropouts and results in each sensing node having a local estimate using global information. In addition, this paper describes both hardware and algorithms used to deploy two sensor nodes for such a task. Two sensor types will be discussed, vision and mm wave radar. The problems introduced by locating the sensors on air vehicles are both interesting and challenging. A total of four unmanned air vehicles will be employed to carry node payloads. Weight and power restrictions of the payloads coupled with the vehicle dynamics make the task of processing and fusing vision and radar based data a challenging problem indeed. This paper aims to highlight many of the problems that have been encountered in developing both hardware and software to operate under such constraints.

W-band airborne interrupted frequency modulated CW imaging radar

A 94 GHz imaging radar-based on the interrupted FMCW (FMICW) principles, with its associated gimbals for stabilization and scanning has been developed as an airborne test-bed to evaluate radar-aided navigation and guidance algorithms. Preliminary results from helicopter-based flight tests show sufficient contrast between selected features (including runways) and their surroundings for both computer- and human-pilot-based guidance. Feature extraction and matching algorithms have shown this system to be more accurate than GPS.

High‐resolution millimeter‐wave radar systems for visualization of unstructured outdoor environments

This paper examines the use of millimeter-wave radar systems for visualization and navigation in unstructured outdoor environments. Three types of radar systems are described. The first is a long range, 94 GHz, frequency modulated interrupted continuous wave radar which is capable of producing two-dimensional (2D) reflectivity images to a range of more than 3 km. This is intended for use in long-range path planning. The second is a class of medium range 77 GHz frequency modulated continuous wave (FMCW) radar with two axis mirror scanners which is capable of producing high resolution threedimensional (3D) imagery out to 500 m at a reasonably slow frame rate. The final class also operates using the FMCW principle, but at 94 GHz, to produce high resolution 2D and 3D images out to about 50 m at a much higher update rate. These shorter range sensors may be used to determine the traversability of the local terrain. The outputs produced by the different classes of radar are examined and the paper considers their advantages when compared to other sensors such as vision and scanning laser. Using radar images, the final section compiles rules for interpreting radar reflectivity images from a path-planning perspective.

Application of Millimetre Wave Radar Sensor to Environment Mapping in Surface Mining

This paper presents the application of a millimetre wave radar technology to environment mapping in surface mining. Sensor requirements for ranging and surface profiling in shovel and dragline operations were determined based on machines performance requirements. Frequency modulated continuous wave (FMCW) technique was selected to achieve the correct range resolution while fast Fourier techniques (FFT) was used to extract the range data from the radar output. Radar data processing was undertaken using stochastic environment representation technique in real-time. The results of field trials show successful radar performance in terms of the systems accurate measurement of excavation terrain, real-time imaging, robustness, reliability and penetration through dust and water

Terrain imaging millimetre wave radar

This paper presents an overview of the work being conducted by the Australian Centre for Field Robotics (ACFR) and the CRC for mining technology and equipment (CMTE) into sensors and systems for real-time environment imaging. Radar is perhaps the only sensor capable of performing imaging tasks in environment where high levels of dust, water vapour, and rain must be contended with. Methods of visualizing the radar data for various applications are presented.