Previous research by many groups has shown that broad-band thermal infrared (TIR) imagers can detect buried explosive threat devices, such as unexploded ordnance (UXO), landmines and improvised explosive devices (IEDs). Broad-band detection measures the apparent temperature - an average over the wave band of the product of the true soil surface temperature and the emissivity. Broad-band detection suffers from inconsistent performance (low signal, high clutter rates), due in part to diurnal variations, environmental and meteorological conditions, and soil surface effects. It has been suggested that hyperspectral TIR imaging might have improved performance since it can, in principle, allow extraction of the wavelength-dependent emissivity and the true soil surface temperature. This would allow the surface disturbance effects to be separated from the soil column (bulk) effects. A significant, and as yet unanswered, question is whether hyperspectral TIR images provide better detection capability (higher probability of detection and/or lower false alarm rate) than do broad-band thermal images. TIR hyperspectral image data of threat objects, buried and surface-laid in bare soil, were obtained in arid, desert-like conditions over full diurnal cycles for several days. Regions of interest containing threat objects and backgrounds were extracted throughout the time period. Simulated broad-band images were derived from the hyperspectral images. The diurnal variation of the images was studied. Hyperspectral was found to provide some advantage over broad-band imaging in detection of buried threat objects for the limited data set studied.
The ability of animals to detect explosives is well documented. Mammalian systems, insects and even single
celled organisms have all been studied and in a few cases employed to detect explosives. This paper will describe
the potential ability of ants to detect, disperse and possibly neutralize bulk explosives. In spring 2008 a team
of DRDC and Itres scientists conducted experiments on detecting surface-laid and buried landmines, improvised
explosive devices (IEDs) and their components. Measurements were made using state-of-the-art short wave
and thermal infrared hyperspectral imagers mounted on a personnel lift. During one of the early morning
measurement sessions, a wispy, long linear trail was seen to emanate several meters from piles of explosives that
were situated on the ground. Upon close visual inspection, it was observed that ants had found the piles of
explosives and were carrying it to their ant hill, a distance of almost 20 meters from the piles. Initial analysis
of the hyperspectral images clearly revealed the trail to the ant hill of explosives, despite being present in
quantities not visible to the unaided eye. This paper details these observations and discusses them in the context
of landmine and IED detection and neutralization. Possible reasons for such behaviour are presented. A number
of questions regarding the behaviour, many pertinent to the use of ants in a counter-landmine/IED role, are
presented and possible methods of answering them are discussed. Anecdotal evidence from deminers of detection
and destruction of explosives by ants are presented.
DRDC Suffeld and Itres Research have collaborated to investigate the use of hyperspectral imaging (HSI) for
surface and buried landmine detection since 1989. Visible/near infrared (<i>casi</i>) and short wave infrared (<i>sasi</i>)
families of imagers have been developed which have demonstrated reliable HSI detection of surface-laid mines,
based on their reflectance spectra, from airborne and ground-based platforms. However, they have limited
ability to detect buried mines. Thermal infrared (TIR) HSI may have the capability to detect buried mines.
Disturbance of quartz-bearing soils has been shown to measurably change their TIR emissivity spectra due to
mixing of surface/subsurface soil (restrahlen band intensities vary with particle size). Some evidence suggests
that the effect can persist months after the visible disturbance has disappeared. Carbonates and other materials
exhibit similar TIR spectral features and heat flow anomalies caused by buried mines can also be measured in the
TIR band. There are no commercially available TIR hyperspectral imagers that are suitable for mine detection.
The very few possibly suitable imagers are one-of-a-kind research instruments, dedicated to internal programs
and not available for the general mine detection community. A TIR hyperspectral imager (<i>tasi</i>) based on a novel
optical design and a cooled MCT focal plane array has been developed. The instrument has been designed with
landmine detection in mind. First light images from the prototype were obtained in summer 2006 and initial
test flights were completed in fall 2006. The design of the instrument and a comparison with design alternatives
in the context of mine detection requirements is discussed. Preliminary images are presented.
DRDC Suffeld and Itres Research have jointly investigated the use of visible and infrared hyperspectral imaging
(HSI) for surface and buried land mine detection since 1989. These studies have demonstrated reliable passive HSI
detection of surface-laid mines, based on their reflectance spectra, from airborne and ground-based platforms.
Commercial HSI instruments collect and store image data at aircraft speeds, but the data are analysed off-
line. This is useful for humanitarian demining, but unacceptable for military countermine operations. We
have developed a hardware and software system with algorithms that can process the raw hyperspectral data
in real time to detect mines. The custom algorithms perform radiometric correction of the raw data, then
classify pixels of the corrected data, referencing a spectral signature library. The classification results are stored
and displayed in real time, that is, within a few frame times of the data acquisition. Such real-time mine
detection was demonstrated for the first time from a slowly moving land vehicle in March 2000. This paper
describes an improved system which can achieve real-time detection of mines from an airborne platform, with
its commensurately higher data rates. The system is presently compatible with the Itres family of visible/near
infrared, short wave infrared and thermal infrared pushbroom hyperspectral imagers and its broadband thermal
infrared pushbroom imager. Experiments to detect mines from an airborne platform in real time were conducted
at DRDC Suffield in November 2006. Surface-laid land mines were detected in real time from a slowly moving
helicopter with generally good detection rates and low false alarm rates. To the authors' knowledge, this is
the first time that land mines have been detected from an airborne platform in real time using hyperspectral
Airborne hyperspectral imaging has been studied since the late 1980s as a tool to detect minefields for military
countermine operations and for level I clearance for humanitarian demining. Hyperspectral imaging employed on
unmanned ground vehicles may also be used to augment or replace broadband imagers to detect individual mines.
This paper will discuss the ability of different optical wavebands - the visible/near infrared (VNIR), shortwave
infrared (SWIR) and thermal infrared (TIR) - to detect surface-laid and buried mines. The phenomenology that
determines performance in the different bands is discussed. Hyperspectral imagers have usually been designed
and built for general purpose remote sensing applications and often do not meet the requirements of mine
detection. The DRDC mine detection research program has sponsored the development by Itres Research of
VNIR, SWIR and TIR instruments specifically intended for mine detection. The requirements for such imagers
are described, as well as the instruments. Some results of mine detection experiments are presented. To date,
reliable day time detection of surface-laid mines in non-real-time, independent of solar angle, time of day and
season has been demonstrated in the VNIR and SWIR. Real-time analysis, necessary for military applications,
has been demonstrated from low speed ground vehicles and recently from airborne platforms. Reliable, repeatable
detection of buried mines has yet to be demonstrated, although a recently completed TIR hyperspectral imager
will soon be tested for such a capability.
DRDC Suffield and Itres Research have jointly investigated the use of visible and infrared hyperspectral imaging for landmine detection since 1988. There has been considerable success detecting surface-laid landmines by classification of their visible/near infrared (VNIR - 400 to 1000 nm wavelength) spectral signatures, but it has not been possible to find VNIR spectral characteristics that would generically distinguish anthropogenic objects from natural features such as rocks, vegetation, soil, etc. Preliminary studies in 1998 suggested that it might be possible to develop such a generic classifier in the short wave infrared (SWIR) and that detection performance might improve. Because of a lack of available SWIR hyperspectral imagers with adequate performance for mine detection, a prototype pushbroom SWIR hyperspectral imager was developed and completed in summer 2002. The now commercially available instrument, <i>sasi</i>, has 160 bands over a spectral range of 850 to 2450 nm, signal to noise ratio of 400:1 with f/1.8 fore-optics, and 600 pixels over a 37.7° field of view. A number of mission flights have been carried out and excellent imagery obtained. In October 2003, Itres and DRDC Suffield personnel obtained field SWIR hyperspectral imagery in the DRDC Suffield Mine Pen of numerous surface-laid mines, one buried mine, other surface-laid human-made items, background materials and people from a horizontally scanning personnel-lift at an altitude of roughly 5 m. Preliminary indications are that a simple generic classification decision boundary should be able to distinguish surface-laid landmines from many human-made artifacts and natural materials. The buried mine was not detected, but the mine had been buried for several years and hence there would be no residual surface disturbance. Furthermore, the small sample size and limited observation time make it difficult to generalize about SWIR performance for buried mines. The instrument is described and the preliminary results of the trial, planned improvements and future research are discussed.
There are currently no fielded technologies for noncontact detection of tripwires. Itres Research Ltd. and DRDC Suffield have been conducting research on optical detection of tripwires since 1996, both for hand-held and vehicle-mounted roles. A proof-of-concept brassboard imager, initially for a vehicle-mounted role, has been constructed. The imager uses a high spatial resolution, panchromatic focal plane array whose high degree of integration includes on-board digitization and flexible addressing capabilities for windowing and subimaging. Command, control and signal processing are accomplished by a computer, based on dual 1GHz Pentium III processors. Using a high level, rapid prototyping language, 1 image frame can be processed in 3 seconds. Straightforward improvements should allow true real-time operation to be achieved. Preliminary testing of the imager was conducted in the outdoor DRDC Suffield Mine Pen in January 2003. Taut, sagging and undulating tripwires of various materials were partially hidden, often nearly invisible to the naked eye, in a number of types of local vegetation. Preliminary, quasi-real-time results showed that many of the wires were detected, although a significant number of false alarms occurred. As expected with the present algorithm, sagging, undulating and highly obscured wires were often difficult to detect. The instrument, results of the trial, planned improvements and future research will be discussed.
A ground vehicle-based, real-time, surface mine detection system, utilizing a Compact Airborne Spectrographic Image (casi), efficient mine detection algorithms, and real-time processing systems, was designed and tested. The combined real-time system was capable of 'learning' the in-situ spectra of various mines, thus providing a spectral library for the detection algorithms. The real-time processing of the casi data involved three steps. The first step was the radiometric correction of the raw data. The second step involved the application of the mine detection algorithms to the corrected data, referencing the spectral library. In the final step, the results of the real-time processes were stored and displayed, usually within a few frame times of the data acquisition. To the authors knowledge, this system represents the first hyperspectral imager to detect mines in real-time. This paper describes the generation of the in-situ mine spectral library, the collection of the scene data, the real-time processing of the scene data and the subsequent display and recording of the detection data. The limitation and expansion capabilities of the real-time system are discussed as well as various techniques that were implemented to achieve the goals. Planned future improvements that have been identified to create a more robust and higher performance, yet simpler processing systems are also discussed.
Research to assess the feasibility of developing a standoff active or passive optical tripwire detector is discussed. Reflectives of typical tripwires and background materials were measured for UV, VNIR and SWIR wavelengths. A breadboard testbed was developed to obtain images of tripwires against various backgrounds for various geometries and a wide range of VU and VNIR wavelengths. Sample images of simulated and real tripwires in uncluttered environments and against typical cluttered backgrounds were acquired and analyzed. Line detection algorithms were applied to the images to detect tripwires. Although detection was not attempted in real-time, analysis showed that available, cost-effective DSPs could potentially execute those algorithms on the images in real-time. The algorithms successfully detected tripwires in a heavily cluttered background and even have the capability to detect partially obscured wires. To complement the measurements, a spreadsheet model was developed to evaluate the merits of different detectors, sources of illumination, wavebands and geometries for different scenarios. Acceptable signal-to- clutter ratios were found for a number of reasonable passive and active illumination scenarios. The study demonstrated that an optical tripwire detector is feasible in principle.
The feasibility of detecting surface-laid and, in some circumstances, buried mines by analysis of visible to near- IR (VNIR) hyperspectral imagery has been demonstrated by the authors in previous studies. An important factor in the practical success of such technology is being able to achieve the necessary spatial and spectral resolution to allow discrimination of mines from background. With some restrictions, both can be improved by increasing the instrument data output rate or decreasing the platform speed and both can be traded off against one another. The optimum trade-off must be determined for a given problem, including the choice of algorithm. Airborne VNIR hyperspectral data were collected over several controlled surface-laid mine fields using a casi hyperspectral imager and a helicopter. The combination of the imager's high speed data recording coupled with the low airspeed of the helicopter enabled the collection of hyperspectral data ranging from four 136 nm wide spectral bands at 10 cm resolution to nine 60 nm wide spectral bands at 20 cm resolution. Each mine field contained a variety of mines ranging form small anti- personnel mines to large anti-vehicle mines. An assessment of the feasibility and practicality of using airborne hyperspectral data to detect various surface-laid mines and mine fields was conducted. In addition, the trade-offs between spectral and spatial resolution for the detectability of surface-laid miens and mine fields are discussed.
A visible wavelength imaging method of identifying surface-laid mines from an airborne platform is described. A Compact Airborne Spectrographic Imager (CASI) collects multispectral radiometric images of mines and backgrounds which are converted to reflectance images using an incident light sensor. Mines are identified by classifying reflectance spectra in two ways. The first classifies individual pixels using the linear correlation coefficient as a measure of spectral similarity while the second classifies spectra using a variant of linear spectral unmixing in which the majority spectral members within an image are treated as background. In scanning manlift imagery of replica mines, targets were discriminated from a variety of background types, even when partially obscured by vegetation, for widely varying illuminations caused by diurnal and seasonal variations, sky conditions, and sun angles. In preliminary practical tests, the CASI was flown over various agricultural fields in which subpixel-size mine-like targets were laid. Visually undetectable targets were detected with good results. Comparison of classifiers revealed that the correlation method is better for high spatial resolution data. When the targets were subpixel in size, the end member analysis had a higher probability of detection than the correlation method, but had more false alarms.
This paper describes a commercially available instrument, CASI (Compact Airborne Spectrographic
imager), designed for remote sensing. The instrument is capable of medium-resolution multispectral
imaging of both local and distant astronomical objects. The instrument employs a GEC UT1O4
CCD to provide an overall spectral resolution of 1.8 nm and a peak quantum efficiency of 10% at
575 nm. The spectral range of the instrument is 450 nm to 900 nm, with 512 active pixels in the
spatial imaging direction. Integration times are variable from several seconds down to 10 ms. A
fiber optic tap intO the spectrograph slit enables a real-time spectral calibration to be recorded with
the data. The results obtained observing several astronomical objects are presented.