Drone SAR Altitude Guide

There are 3 functions of remote sensing that are relevant to missing person searches, each requiring greater resolution to accomplish:

• Detection: the ability to distinguish an object from the background (e.g., heat source, white/orange object)
• Recognition: the ability to determine what type of object has been detected (e.g., person, bird, buoy, etc.)
• Identification: the ability to determine the exact identification of the object (e.g., whether it is the missing person or a different person)

Importantly, each of these functions have a different effective resolution, i.e., the number of pixels the object needs to be on your screen to detect, recognise or identify it. A widely used criterion for minimum resolution requirements for imagery is Johnson’s Criteria, based on the work of John Johnson for the U.S. Army. Johnson’s Criteria is usually referenced in terms of achieving a 50% probability for each function; however, the International Aeronautical Maritime Search and Rescue Manual calculates that a 79% probability is more optimal during a search. Therefore, the longest edge of a search object must subtend:

• Detection: 4 pixels
• Recognition: 15 pixels
• Identification: 25 pixels

References:

• NSARC, 2016. Unmanned Aircraft System (UAS) Search and Rescue Addendum to the National Search and Rescue Supplement to the International Aeronautical and Maritime Search and Rescue Manual Version 1.0. USA: NSARC.
• IMO & ICAO, 2019. IAMSAR Manual 2019 Edition.