Analysis of Visual Detection Performance (Fall 1978 Experiment)

From 11 September 1978 to 6 October 1978 a visual detection experiment was conducted in Block Island sound by the U.S. Coast Guard Research and Development Center. It was the first in a series of experiments designed to improve search planning guidance contained in the National Search and Rescue Manual. This was a controlled experiment involving 82 and 95 foot cutters, 41 and 44 foot boats, helicopters, and fixed wing aircraft searching for white 16 foot boat targets anchored at predetermined locations within the search area. Through the use of a microwave ranging system, the positions of searchers and targets could be accurately reconstructed to determine the lateral range of targets that were detected, as well as targets not detected. Thus, probability of detection versus lateral range curves could be developed, and, by integrating these curves, sweep width could be determined as well. A total of 695 detection opportunities were generated. A sophisticated binary multivariate logistic regression computer program was used to develop sweep width estimates for the environmental conditions experienced. Of the eight visual detection parameters investigated, visibility, wind speed, swell height, cloud cover, search unit type, and duration of search were determined to have a significant effect on sweep width. The sweep width is an excellent measure of search unit performance. A more rapid degradation of sweep width was found for deteriorating environmental conditions than is now predicted by the National Search and Rescue Manual. The methods used to conduct this experiment and analyze the data were found to be successful, and are recommended for future experiments.