Drone SAR Altitude Guide

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

• The ability to distinguish an object from the background (e.g., heat source, white/orange object)
• The ability to determine what type of object appears on the screen 
• The ability to determine the exact object we are looking at 

Importantly, each of these functions have a different effective resolution, i.e., the number of pixels the object needs to be on your screen. 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.

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.