Search theory allows for correction factors to account for conditions (such as night) that affect the sweep width value. Search theory also predicts that the coverage is proportional to the probability of detection by either the inverse cube curve or exponential function (random search). The objective is to determine the correction factors from night searching, use of IR detection devices and validate the coverage curves.
Effective Sweep Width experiments were conducted in the same location with the same medium visibility adult-sized targets during both the day and the night in a temperate forest. Additional experiments examined the impact of one, two, and three person teams. In addition, high and low visibility clue-sized objects were placed directly on the trail. Low visibility human subjects were used for infrared detection.
We found an effective sweep width of 64 meters during the daytime and 22 meters at night for a correction factor of 0.34 for the adult-sized targets. Both high (100% vs 94%) and low (83% vs 43%) visibility clues were more detectable during the day versus night (P<0.001). Searchers with dim flashlights (<200 lux at one meter) resulted in an additional correction factor of 0.5. The use of IR at night increased the sweep width to 68 meters. Two searchers increased the sweep width value by 1.3, however, three searchers didn’t see a statistical increase. The probability of detection versus coverage plots of both day and night experiments fell between the inverse cube and exponential curves.
Additional experiments have been conducted to examine the sweep width factors generated from both electro-optical and Infrared sensors on a UAV platform. Sweep width values and important correction factors will be examined which will impact search patterns.This single experiment for only one visibility class of search target showed that visual searching is significantly degraded by searching at night. The daytime coverage suggests the inverse cube model while the night coverage suggests an interim result. The use of effective sweep width, correction factors, and validated coverage curves can lead to more accurate assessments of the probability of detection.