## 1 Introduction
### Sensor deployment and target detection distance  
Search strategy is the means used to maximize target detection. This concept is applied at different scales, for example an incident commander searching for a lost person might employ a search strategy that involves foot searchers, aircraft, and search dog teams. At this level the objective is to maximize resource allocation based on probability of area (POA), the likelihood that the target is in a defined region. At a micro scale, search strategy is the actual pattern a searcher uses to search a vector, such as a vehicle, a building, or a geographic area. Ideally search strategy is optimized to minimize time worked and distance covered while maximizing the number of targets found. Even with an optimized search strategy, target detection ultimately rests on the ability of the search tool whether human, dog, or synthetic sensor. Chemosensor operators also employ search strategy; it can be as simple as placing a sensor in a ventilation return duct to detect compounds in a room or as complex as a systematic grid pattern through a room or area. Search strategy has been investigated for different applications from theoretical [22] to animal predation and foraging [23] to sampling of rare species ([24], [25]) among others [26]. Olfaction-based detection distance by dogs and search strategy are interrelated but the relationship between the two has not been quantified. Detection distance is simply how far away a target is detected, independent of the sensory means employed. In the context of considering a detection dog to be a chemical sensor, detection distance is the point where the dog exceeded its minimum detection limit, since it was able at that moment to detect and identify (recognize) the target source. This is not necessarily the maximum detection limit for those conditions since scent pools vary in shape and size as described above. Therefore, detection distance varies not only with detection threshold of the dog, but also with the physical shape of the odor concentration distribution. For humans, target detection such as tortoises, scat, missing people, landmines, or buried items to name a few is based primarily on visual or sometimes auditory clues. Efficacy of night searching, searching in low light conditions, or searching in dense vegetation or other type of cover by humans is therefore very limited. Similarly for animals, visual detection ability is affected by the quality of the surrounding medium such as air or water. Visual detection distance has been investigated as a function of light level and turbidity in fish and related predator-prey detection of each other [27]. Such responses can be explored with theoretical models that describe the role of detection distance between predators and prey in escape behavior [28]. One study [29] evaluated the relationship between the distance birds detected a predator and subsequent escape behavior. In detection work, dogs acquire and use olfactory search images [30] and have been shown to rely primarily on olfaction to detect stationary and cryptic or buried objects [31]. Together, detection distance and search strategy affect the probability of detection (POD), which is the likelihood that a target will be located. In detection dog disciplines POD is reported as a percentage. For wildlife detection applications, where large areas or long distances are to be searched, it is important to first determine POA based on best available information about the species and its habitat, and subsequently within the selected search areas determine a search strategy to achieve the desired POD. Although a 100% POD is always desirable, in the field setting it is not a realistic expectation ([20], [10]). Studies on the effectiveness of dogs in the field setting have returned varying results [15], but dogs have been shown to be quite capable of detecting targets under natural search conditions ([32], [3], [33]).