Philip Church

Electrical Impedance Tomographic Imaging of Buried Landmines

A prototype confirmation landmine detector, based on electrical impedancetomography (EIT), which can operate under realistic environmental conditions, has been developed. Laboratory and field experiments demonstrated that it is possible to reliably reconstruct, on the scale of the electrode spacing (ES) (in width and depth), conductivity perturbations due to a shallow buried antitank mine or a similar object in a variety of soils (black earth, clay, sand) down to depths equal to the dimensions of the object (1-1.5 ES, equivalent to 14-21 cm for a 64-electrode 1 m times 1 m array). These represent the first EIT images of real landmines computed from measured data. Occasional problems were encountered with the electrical contact in very dry soils, with excessive insertion pressure being required for reliable electrode contact. However, poor contacts could be detected, and the offending probe was either reinserted or compensation was applied. A matched filter detection algorithm based on a replica of the object of interest was developed and shown to effectively reduce the false alarm rate of the detector. EIT is especially suited for wet lands and underwater, where other mine detectors perform poorly. Experiments in a water-and sediment-filled tank have demonstrated that detection of minelike objects in such an environment with a submerged array is feasible. These experiments represent the first EIT measurements of targets using an electrode array submerged underwater. EIT may also have an application in locating intact mines in the berms formed by mine-clearing equipment. The EIT sensor head could be made cheaply enough to be disposable and remotely inserted to improve safety

Characterization of the OPAL obscurant penetrating LiDAR in various degraded visual environments

The OPAL obscurant penetrating LiDAR was developed by Neptec and characterized in various degraded visual environments (DVE) over the past five years. Quantitative evaluations of obscurant penetration were performed using the Defence RD Canada – Valcartier (DRDC Valcartier) instrumented aerosol chamber for obscurants such as dust and fog. Experiments were done with the sensor both at a standoff distance and totally engulfed in the obscurants. Field trials were also done to characterize the sensor in snow conditions and in smoke. Finally, the OPAL was also mounted on a Bell 412 helicopter to characterize its dust penetration capabilities, in environment such as Yuma Proving Ground. The paper provides a summary of the results of the OPAL evaluations demonstrating it to be a true “see through” obscurant penetrating LiDAR and explores commercial applications of the technology.

Imaging of Compact Objects Buried in Underwater Sediments Using Electrical Impedance Tomography

A detailed study is undertaken to investigate the performance and phenomenology of electrical impedance tomography for underwater applications. Experiments are performed in an aquarium tank filled with water and a sediment layer. A 64-electrode square array, appropriately scaled down in size, and a previously developed data acquisition system are used. An evaluation is conducted of the ability to detect compact objects buried at various depths in the sediment, with different horizontal separations, and at various vertical separations between the electrode array and the sediment layer. The objects include metallic and nonmetallic mine-like objects and inert ammunition projectiles, all appropriately scaled down in size. The effects of a number of other physical factors are studied, including sediment type, water turbidity and salinity, and object coating integrity and rusting.

Performance assessment of an electrical impedance tomography detector for minelike objects

This paper reports the results of the performance assessment of an Electrical Impedance Tomography detector (EIT) for mine-like objects in soils. EIT uses an array of electrodes to inject low frequency currents in the soil and measure the resulting electrical potentials. The measurements are then used to reconstruct the electrical conductivity perturbations underneath the array. In the course of this work, an EIT instrument was built and field evaluated. The array is made of 64 stainless steel stimulating and recording electrodes arranged in an 8x8 grid. Specialized electronics has been built to control the electrode current stimulations and potential measurements. The detection algorithm is tuned to objects of a given size and shape to reduce the false alarm rate. The main mechanical, electronic and algorithm components of the detector will be presented. The EIT detector was originally designed in view of evaluating its potential as a confirmatory detector of AT mines. To that end, mine-like objects representative of some AT mines were used. Results of preliminary field evaluations are presented. The detection capabilities and limitations of mine-like objects are discussed.

Laboratory Evaluation of the EIT Technology Capability to Detect Mines Buried in an Underwater Sediment Layer

The work reported in this paper is focused on the particular problem of detecting mines buried in the sediment layer of shallow water environments. This is relevant to the detection of mines buried in beaches, surf zone or wet agricultural areas such as rice paddy fields. A reduced scale Electrical Impedance Tomography (EIT) detector is used in a laboratory setting to evaluate the capability of the EIT technology to detect mine-like objects buried in a layer of sand, underwater. Detection results are presented for two correlation methods developed using signatures measured for known mine-like objects located at several relative positions with respect to an electrode array. Discrimination results are also presented for two mine-like objects of similar shape and different size. Finally, recommendations are made for future research and implementation.

Mapping of ice, snow and water using aircraft-mounted LiDAR

Neptec Technologies Corp. has developed a family of obscurant-penetrating 3D laser scanners (OPAL 2.0) that are being adapted for airborne platforms for operations in Degraded Visual Environments (DVE). The OPAL uses a scanning mechanism based on the Risley prism pair. Data acquisition rates can go as high as 200kHz for ranges within 240m and 25kHz for ranges exceeding 240m. The scan patterns are created by rotating two prisms under independent motor control producing a conical Field-Of-View (FOV). An OPAL laser scanner with 90° FOV was installed on a Navajo aircraft, looking down through an aperture in the aircraft floor. The rotation speeds of the Risley prisms were selected to optimize a uniformity of the data samples distribution on the ground. Flight patterns simulating a landing approach over snow and ice in an unprepared Arctic environment were also performed to evaluate the capability of the OPAL LiDAR to map snow and ice elevation distribution in real-time and highlight potential obstacles. Data was also collected to evaluate the detection of wires when flying over water, snow and ice. Main results and conclusions obtained from the flight data analysis are presented.

Overview of the commercial OPAL LiDAR optimized for rotorcraft platforms operating in degraded visual environments

Neptec has developed a family of obscurant-penetrating 3D laser scanners called OPAL 2.0 that are being adapted for rotorcraft platforms. Neptec and Boeing have been working on an integrated system utilizing the OPAL LiDAR to support operations in degraded visual environments. OPAL scanners incorporate Neptec’s patented obscurantpenetrating LiDAR technology which was extensively tested in controlled dust environments and helicopters for brownout mitigation. The OPAL uses a scanning mechanism based on the Risley prism pair. Data acquisition rates can go as high as 200kHz for ranges within 200m and 25kHz for ranges exceeding 200m. The scan patterns are created by the rotation of two prisms under independent motor control. The geometry and material properties of the prisms will define the conical field-of-view of the sensor, which can be set up to 120 degrees. Through detailed simulations and analysis of mission profiles, the system can be tailored for applications to rotorcrafts. Examples of scan patterns and control schemes based on these simulations will be provided along with data density predictions versus acquisition time for applicable DVE scenarios. Preliminary 3D data acquired in clear and obscurant conditions will be presented.

Electrical impedance tomography for underwater detection of buried mines

The detection of buried land mines in soil is a well-studied problem; many existing technologies are designed and optimized for performance in different soil types. Research on mine detection in shallow water environments such as beaches, however, is much less developed. Electrical impedance tomography (EIT) shows promise for this application. EIT uses current-stimulating and voltage-recording electrode pairs to measure trans-impedances in the volume directly beneath the electrode array, which sits flat over the ground surface. The trans-impedances are used to construct a conductivity profile of the volume. Non-metallic and metallic explosives appear as perturbations in the conductivity profile, and their location and size can be estimated. Lab testing has yielded promising results using a submerged array positioned over a sand bed. The instrument has also successfully detected surrogate mines in a traditional soil environment during field trials. Resolution of the detector is roughly half the pitch of electrodes in the array. In underwater lab testing, non-conducting targets buried in the sand are detected at a depth of 1.5 times the electrode pitch with the array positioned up to one electrode pitch above the sand bed. Results will be presented for metallic and non-metallic targets of various shapes and sizes.

Evaluation of a steerable 3D laser scanner using a double Risley prism pair

Laser scanners based on Risley prism pair technology offer several advantages, including a multitude of scan pattern generation, non-overlapping patterns, and a conical Field-Of-View (FOV) generating a high data density around the center. The geometry and material properties of the prisms define the conical FOV of the sensor, which can be typically set between 15° to 120°. However, once the prisms are defined, the FOV cannot be changed. Neptec Technologies in collaboration with Defence Research and Development Canada has developed a unique scanner prototype using two pairs of Risley prisms. The first pair defines a small 30° FOV which is then steered into a larger 90° Field-Of-Regard (FOR) by using the second pair of prisms. This presents the advantages of a high-resolution scan pattern footprint that can be steered quickly and randomly into a larger area, eliminating the need for mechanical steering equipment. The OPAL Double Risley Pairs (DRP) prototype was recently evaluated at Yuma Proving Ground with the scanner positioned atop a tower and overlooking various types of targets while dust was generated by a helicopter. Results will be presented in clear and dusty conditions, showing examples of moving a high resolution FOV within the FOR.

Characterization of the OPAL LiDAR under controlled obscurant conditions

Neptec Technologies’ OPAL-120 3D LiDAR is optimized for obscurant penetration. The OPAL-120 uses a scanning mechanism based on the Risley prism pair. The scan patterns are created by rotating two prisms under independent motor control. The geometry and material properties of the prisms define the conical field-of-view of the sensor, which can be built to between 60 to 120 degrees. The OPAL-120 was recently evaluated using a controlled obscurant chamber capable of generating clouds of obscurants over a depth of 22m. Obscurants used in this investigation include: Arizona road dust, water fog, and fog-oil. The obscurant cloud optical densities were monitored with a transmissometer. Optical depths values ranged from an upper value of 6 and progressively decreased to 0. Targets were positioned at the back of the obscurant chamber at a distance of 60m from the LiDAR. The targets are made of a foreground array of equally spaced painted wood stripes in front of a solid background. Reflectivity contrasts were achieved with foreground/background combinations of white/white, white/black and black/white. Data analysis will be presented on the effect of optical densities on range and cross-range resolution, and accuracy. The analysis includes the combinations of all obscurant types and target reflectivity contrasts.