Eyes in the Sky: Using Drones to Measure Sea Turtles

By fisheries.noaa.gov.

What do drones and toy turtles have in common? Scientists are using these tools to measure sea turtles in the wild without ever touching them.

Drones not only take great photographs—they can also be used to take measurements. In our case, we use them to measure the size of sea turtles seen in the wild.

Photogrammetry is the process of getting reliable measurements from photographs. This technique has been used for more than 100 years, primarily to create maps from aerial photos. With advanced drone technology, biologists are using photogrammetry to measure sea turtle species like leatherbacks, loggerheads, and Kemp’s ridleys.

Collecting size information using photogrammetry helps us understand what age groups of different sea turtle species are using which areas, and when. For example, scientists from NOAA’s Southeast Fisheries Science Center recently used this method to measure juvenile green sea turtles in coastal Louisiana. At another site in North Carolina, we saw and measured adult and juvenile loggerhead sea turtles. This might suggest that different species of turtles occur within different regions. Collecting information on size and habitat use informs conservation management strategies and helps assess progress toward recovery. Another benefit: measurements can be made without having to capture and handle the turtles. This means more animals can be measured in a day and the turtles don’t even know we’re there.

How Photogrammetry Works

A diagram of a drone flying above a sea turtle.
Photogrammetry uses:
  • Basic features of the drone’s camera (focal length and sensor width)
  • Height or altitude the drone was flying when the picture was taken
  • Image width of the picture in pixels

By combining this information, we can determine the ground sampling distance which is how much actual area is represented in each photo pixel. Special software is then used to measure the turtles’ length in pixels and multiply it by the ground sampling distance.