68 Proceedings Spring 2025 range curve (LRC). The lateral range curve quantifies the probability of detecting the search object as a function of the range between the search asset and the object. All variables that impact probability of detection other than range are accounted for within the shape of the LRC. Therefore, a change to any variable will result in a different LRC. The Coast Guard Research and Development Center (RDC) has developed LRCs and associated sweep widths that have been used by the service and international mar- itime SAR community since the late 1970s. Historically, the development of LRCs has largely been based on extensive field experiments. Throughout these experi- ments, search objects of interest—simulated people in the water, life rafts, and small boats—were anchored in an area and search assets would proceed through the area along a specified path. Data were collected regard- ing several factors, including: • The search asset and sensor—was it conducted with naked eye or night vision goggles? • Search parameters like speed and altitude of the search asset • The search object, including its size • Environmental conditions like wind speed and meteorological visibility • When the search assets detected objects throughout the search pattern All collected data were then analyzed to calculate the necessary LRCs. There are more than a dozen variables which can impact an LRC, many of which, like environmental con- ditions, cannot be fully controlled while conducting field experiments. Therefore, collecting sufficient data in each of the possible combinations of variables is not feasible. Early approaches to compute LRCs defined methods of interpolating and extrapolating the data collected in the field to the broader expanse of variables. While effective, this approach still requires thou- sands of data points across varied environmental conditions per sen- sor, search asset, and object combi- nation. Collecting this amount of data is made even more challenging by the rate at which new sensors are available and integrated with Coast Guard assets. Modernizing Lateral Range Curve Development In recent years, the RDC has exam- ined means of reducing the demand for empirical data when computing LRCs. Nearly 20 commercial and government off-the- shelf, physics-based models were evaluated. These tools, for either radar or electro-optic/infrared (EOIR) sensors, were capable of computing either instantaneous prob- ability of detection as a function of range or information about how the search object appears in the environment. For example, to predict effectiveness of an infrared sen- sor it is necessary to know the amount of heat emitted by an object within the environment. Given that no model inherently computes LRCs, the RDC has established methods for translating the aspect- dependent—detectability of a vessel viewed head-on compared to viewed from the side is very different—instan- taneous probability of detection as a function of range into an LRC. These previous efforts have defined a new pro- cess that uses physics-based models to predict the lateral range curves of human-in-the-loop sensors, and lever- ages small, targeted field experiments to validate the pre- dictions. The RDC’s Data, Modeling, & Decision Support Research Program is continuing to evaluate this new approach to calculating LRCs, with plans to validate the physics-based models against empirical data collected in accordance with the historical approach. Accurate LRCs are a crucial SAROPS input, enabling the Coast Guard to maximize its probability of finding mariners in distress as effectively as possible. About the authors: Grace Python serves as an operations research analyst in the Coast Guard Office of Search and Rescue (Coast Guard-SAR) Policy Division. Prior to joining Coast Guard-SAR, she spent seven years at the Coast Guard Research and Development Center as an operations research ana- lyst, predominantly conducting SAR-related research. LT Ardy Effendi graduated from the U.S. Coast Guard Academy in 2016 and served aboard multiple Coast Guard cutters and as commanding officer of the Coast Guard Patrol Forces Southwest Asia cutter relief crew. After completing his master’s degree in operations research at North Carolina State University in 2020, he reported to the Coast Guard Research and Development Center. 0 Lateral Range (closet point of approach) Maximum range of target detection Target missed inside sweep width Target detected outside sweep width Target detected outside sweep width Sweep width (w) 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 Pd Since the late 1970s, the Coast Guard Research and Development Center has developed lateral range curves, like those shown here, and their corresponding sweep widths. Coast Guard graphic
