67 Spring 2025 Proceedings SAR Research How lateral range curves improve rescues by Grace pythoN Operations Research Analyst Office of Search and Rescue U.S. Coast Guard Lt ardy eFFeNdi Data Analyst Research and Development Center U.S. Coast Guard U .S. Code states that the Coast Guard “shall develop, establish, maintain and operate SAR facilities and may render aid to distressed per- sons and protect and save property on and under the high seas and waters subject to the jurisdiction of the United States.” The Coast Guard’s jurisdiction encompasses more than 3.4 million nautical square miles in which the ser- vice may conduct search and rescue (SAR) operations for persons in distress. On an average day, the Coast Guard responds to 45 SAR cases. Some of these cases require assistance, but there is no search involved—an individ- ual requires a medical evacuation, or a vessel is disabled and needs help. For some cases, there is uncertainty about the exact location or condition of the people in distress, which could require a search across an expansive area. For example, a vessel taking on water is able to send a may- day call with an approximate location before communi- cations are lost. Even as the Coast Guard immediately initiates a response, there is uncertainty regarding the vessel’s exact position when it went into distress and the object the response team is searching for. Are there individuals still on the vessel or did they abandon ship to a life raft? Perhaps they are in the water, and if they are in the water, are they wearing personal floatation devices? Each of these potential search objects will drift in unique ways based on their geometry and the winds and currents in their area. To deal with all these aspects of uncertainty, iden- tify the likely location or locations of objects, and plan effective searches, the Coast Guard uses the Search and Rescue Optimal Planning System (SAROPS). Developed by the Coast Guard, SAROPS is a tool that simulates thousands of possible particles, each representing an individual search object, to account for position and time uncertainty associated with the distress and the winds and currents in an area. This information is used to determine the probability that an object will be in a given location at a given time. Once probable locations are identified, SAROPS is used to determine an effective pattern for searching the area of interest with the available search assets including those from Coast Guard, other government agencies, and other boaters. Developing a search pattern requires an understanding of how effective any search is at finding the objects of interest. As a simplified example, consider mowing your lawn. Lawns are often mowed in long, parallel lines because the mower is 100% effective along the path it travels. To achieve efficient coverage of the entire lawn, the distance between these parallel lines should match the length of the mower’s blade. This is a well-defined example; the mower is 100% effective where it is used and 0% effective everywhere else. However, sensors used while searching during a SAR case are rarely 100% effective out to a given range. Sensor effectiveness generally decreases as the distance between the sensor and the search object increases, but that rate of decrease is dependent on numerous factors including: • The type and size of search object(s) • Environmental conditions on the scene • The type of search asset employed—helicopter, fixed-wing aircraft, small boat, or cutter All these factors are accounted for through a lateral This image shows an example of the probability distribution of where an object is likely to be at a specific time given all the uncertainty associated with a case, where the purple sections in the center are more likely, and blue sections are less likely. Coast Guard graphic
