Visual detection of soil disturbances is a surprisingly effective, but far from perfect way of detecting buried explosive threats such as landmines and improvised explosive devices (IEDs). This effort builds upon the few systematic studies of optical detection in this area. It investigates observer sensitivity to optical information produced by the burial of anti-tank and small anti-personnel landmines asking “How detectable are disturbed soil signatures captured in visible (VIS), shortwave infrared (SWIR), and thermal infrared (TIR), bands?” “Which band or bands are most effective for detection?” and “How well does each band support detection in the natural environment over time?” Using signal detection procedures this study presented young adults photographs showing soil disturbed by landmine burial or adjacent undisturbed surfaces with instructions to make decisions about the presence or absence of a disturbance. Stimuli spanned a six-week time period over which VIS, SWIR, and TIR imagery was collected. Results show that (a) signal strength persists surprisingly well over the observation period, (b) generally, SWIR and VIS show consistently strong performance for large anti-tank mines and SWIR shows the soil signature for the small, anti-personnel mine remarkably well. TIR lags the other two bands when using d’ to measure performance, but shows promising hit rates for anti-tank mine signatures under appropriate conditions. Generally, results show that the SWIR and VIS bands show most promise as a practical means of explosive hazards detection, although TIR can work effectively for large anti-tank mines under certain conditions. Limitations and implications for further research are discussed.
The burial of objects disturbs the ground surface in visually perceptible ways. This project investigated how such
information can inform detection via imaging from visible through mid-infrared wavelengths. Images of the ground
surface where objects were buried were collected at multiple visible through mid-infrared wavelengths prior to burial
and afterward at intervals spanning approximately two weeks. Signs of soil disturbed by emplacement change over time
and exposure in the natural environment and vary in salience across wavelengths for different time periods. Transient
cues related to soil moisture or illumination angle can make signatures extraordinarily salient under certain conditions.
Longpass shortwave infrared and multi-band mid-infrared imaging can enhance the signature of disturbed soils over
visible imaging. These findings add knowledge and understanding of how soil disturbances phenomena can be exploited
to aid detection.
Objects buried in unimproved surfaces can be inferred from the disturbance of the soil above them. We have found for
mines emplaced according to U.S. military doctrine in clay-rich soils, that imaging at visible, shortwave infrared, and
thermal infrared are effective at different times under various illumination conditions, and that these techniques can be
synergistic. Complementary visible - thermal infrared laboratory spectral measurements show that grain size differences
associated with disturbed soils can make them more reflective or emissive than undisturbed soils. However, the field
measurements demonstrate that grain size effects are not significant under passive visible and shortwave infrared
illumination. Instead, shortwave infrared (1.55 - 1.7 μm) imaging, in particular, is effective because the roughened
disturbed soil casts a pattern of shadows under a wide range of illumination conditions that are also emphasized by a
background of undisturbed soil possessing few contrast variations.
Can human vision supplement the information that handheld landmine detection equipment provides its operators to
increase detection rates and reduce the hazard of the task? Contradictory viewpoints exist regarding the viability of
visual detection of landmines. Assuming both positions are credible, this work aims to reconcile them by exploring the
visual information produced by landmine burial and how any visible signatures change as a function of time in a natural
environment. Its objective is to acquire objective, foundational knowledge on which training could be based and
subsequently evaluated. A representative set of demilitarized landmines were buried at a field site with bare soil and
vegetated surfaces using doctrinal procedures. High resolution photographs of the ground surface were taken for
approximately one month starting in April 2006. Photos taken immediately after burial show clearly visible surface
signatures. Their features change with time and weather exposure, but the patterns they define persist, as photos taken a
month later show. An analysis exploiting the perceptual sensitivity of expert observers showed signature photos to
domain experts with instructions to identify the cues and patterns that defined the signatures. Analysis of experts' verbal
descriptions identified a small set of easily communicable cues that characterize signatures and their changes over the
duration of observation. Findings suggest that visual detection training is viable and has potential to enhance detection
capabilities. The photos and descriptions generated offer materials for designing such training and testing its utility.
Plans for investigating the generality of the findings, especially potential limiting conditions, are discussed.
Studies show that soldiers' mine detection capabilities with the PSS-12 hand-held detector are substandard and that their probabilities of detecting (PD) low-metal mines are dangerously low. Highly experienced PSS-12 operators, however, achieve PDS over 0.90 on high- and low-metal anti- tank (AT) and anti-personnel (AP) mines. Significantly, experts' detection techniques differ from conventional military PSS-12 operating procedures. We report three studies investigating whether instruction based on expert skill could bridge the observed performance gap. Basic research on human expertise has shown that instruction based on detailed scientific analyses of experts' behaviors and thought processes boosts skill acquisition dramatically. These studies tested the effects of an experimental detection training program based on knowledge and techniques learned from analysis of PSS-12 expertise. In Study I soldiers who had completed standard mine detection training participated as operators/trainees. This experiment used a pretest-posttest design. Mine simulants served as targets in testing gand training. Targets simulate d5 different mines and represented high- and low-metal AT and AP mine types. Pretest performance failed to distinguish the treatment and control groups. Both achieved very low PDs on low metal mines. Treatment-group soldiers then received approximately 15 hours of experimental, hands-on training. Posttest results showed that the treatment groups PD on minimal metal targets was more than 6 times that of the control group. Study 2 tested a subset of the treated soldiers in the same setting, now wearing body armor. Results replicated those of Study 1. Study 3 tested treatment group soldiers on real mine targets. Several mines from each mine type were used. The surface of the test lanes was expected to increase detection difficulty. Soldiers nonetheless achieved an aggregate PD of 0.97 and showed significant improvement in detecting low-metal mines.
This paper describes findings from a study conducted to analyze the behavior, knowledge, and thinking that support the highest levels of human land mine detection skill. A recent assessment of land mine detection capability concluded that 'human operators perform better with any detector system than the corresponding fully automated system.' This assessment, plus evidence linking individual differences in detection ability to experience, suggests that methods, data, and theory developed in studying human expertise can be applied to the problems of land mine detection and discrimination. Studies of experts across a variety of skill domains have demonstrated that analyses of experts' skills can yield findings useful for designing efficient and effective training programs and supporting technology development. This initial field study was performed to (a) identify the upper levels of human mine detection capability using currently-fielded hand-held equipment and (b) model the knowledge, thickening, and techniques employed by proficient human operators. Two experienced operators showed sufficiently impressive detection performance to qualify as experts. Data laos show that skilled PSS-12 operator can detect low-metal mines with considerable accuracy. A first-approximation information- processing model of expert operator skill is presented that is based on observation of the operators' activities as they searched for mine targets.
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