Drone SAR Altitude Guide

What is the optimal altitude for finding a missing person?

Watch Video  

Complete this quick survey as part of your pre-flight checks to produce sample thermal and visual images of how big the missing person might appear on your screen.

This helps to “calibrate” your eyes and find out if your parameters are optimal for each function of remote sensing (detection, recognition, and identification).


Learn More About Remote Sensing

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


  • 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.

Learn More About Our Setup

Drone: DJI Mavic 2 Enterprise Advanced

Screen: Built-in screen on the DJI Smart Controller

Missing person characteristics:

  • Height: 5ft11
  • Weight: 105kg
  • Body temperature: 36.9oC (recorded by Tympanic method)
  • Sex: Male
  • Age: 30
  • Clothing: black clothing


  • Air temperature: 5oC
  • Terrain: Flat with vegetation at 10.3cm tall

To stay in touch and receive ebooks, resources, and product updates, subscribe to our newsletter.