Cranes and Drones: Strange Airfellows?

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When U.S. Geological Survey (USGS) biologist Leanne Hanson answered a “call” in 2009 for interested USGS scientists to learn to operate drones, she knew it would be uplifting work—literally. Recently, as a newly trained and certified pilot, she spent a week flight-testing a small unmanned aircraft system, also called an sUAS1 or simply a drone, as a non-invasive means of conducting aerial counts o

The collaborative project Hanson is working on is called “proof of concept”—meaning that they are testing the drones to see if they will be an effective means of conducting aerial counts of skittish creatures like migrating sandhill cranes.

“It was really interesting,” reports Hanson, a biologist with the USGS Fort Collins Science Center (FORT) in Colorado. “We flew the sUAS over the cranes when they were roosting, feeding, and loafing to see how they reacted. They sat still for us when they were roosting and loafing, but birds flushed during feeding. We will plan missions during roosting and loafing times, when their behavior is not affected.”

Taking Recycling to New Heights

In a demonstration of the utility of military technology to scientific research, the U.S. Army transferred 15 decommissioned Raven A sUASs to the USGS Unmanned Aircraft Systems (UAS) Project Office for use in natural resource field projects. One of those projects involves Hanson and the sandhill cranes that migrate through the Monte Vista National Wildlife Refuge in central Colorado’s San Luis Valley.

In the first application of the Raven system to a natural resource management need, the USGS and U.S. Fish and Wildlife Service (FWS) are comparing the sUAS video imagery with simultaneously collected data from ground-based counts to estimate the population of sandhill cranes migrating through the San Luis Valley. Cranes are large, upright birds (up to 4 ft tall) that move through the refuge in early spring. The birds can be counted while aggregated in this important “staging area” on their migratory route.

Scientist Leanne Hanson releasing a Raven droan into the air.
FORT scientist Leann Hanson releasing the Raven into the air. 

Typically, Hanson says, fixed-wing aircraft are used to conduct surveys of everything from vegetation cover to wildlife populations. This is an expensive and somewhat risky practice, but has been the only feasible way of getting accurate information without field staff spending hours trying to collect data on the ground. In the case of sandhill cranes, which spread out over several square miles of staging area, aerial surveys are the only viable way to obtain reliable population estimates.

“Basically, if the drones don’t scare the birds and the imagery is clear enough for counting cranes, the drones can quickly cover more territory and see more ‘at a glance’ than field personnel on the ground. That not only saves time, money, and fuel, but could also generate more precise estimates,” says Hanson. “Plus, some places are just difficult to access on foot, while a drone can simply fly in.” 

The FWS, which manages the Monte Vista National Wildlife Refuge, hopes sUASs use will prove to be a safer (for both birds and low-flying pilots) and more cost-effective means of conducting migratory bird population assessments, with the least risk of disturbing migrating birds.

Questions the crane study is designed to answer are:

  • Does the vehicle, which buzzes loudly in hand but fades out as it achieves altitude, frighten and flush the birds? Or how will they react?
  • If the drone reaches an altitude where it does not cause a reaction in the birds, can the birds still be seen well enough to count?
  • How do views compare between the two different camera types used on the drones? (The electro-optical camera records natural color, like a regular camera; the infrared camera senses heat, which shows up as either white or black shapes on a gray background.)
  • Finally, if an sUAS works for population surveys, how closely do these aerial counts align with those conducted by observers on the ground?

Early Returns

Click here to watch the Raven A video

Scientist Chris Holmquist-Johnson holding a Raven UAS. USGS photo.

Raven A specs:

Length: 36 in

Wingspan: 55 in

Weight: 4.2 lb 

Operating Altitude: 150–1,000 ft AGL (above ground level)

Cruising Speed: 30 mph

Range: 10 km

Flight duration: 60-90 min

Power: Lithium-ion rechargeable battery

Hanson and the project team flew the Raven at various altitudes, starting at their approved maximum of 400 ft above ground level, then decreasing each subsequent flyover by 50 ft until they reached the nominal altitude of 150 ft, the minimum height allowed in the Federal Aviation Administration’s Certificate of Authorization [see box below, How sUASs Work]. Simultaneously the team recorded for each flight (1) any disturbance to the birds and (2) the Raven’s height above ground in order to identify correlations between the two. They also tested the efficacy of each type of camera, since only one can be mounted at a time on the drone.

Although the pilot study is not yet completed, preliminary results are promising.

“We were amazed at the image clarity using the NADIR [down-looking] infrared camera at 200 ft above ground level. We located roosting cranes that our ground-counters didn’t know were there—just one example of how we can improve population counts using this technology,” says Hanson. “Also, early morning, low-light flights are too dangerous for manned aircraft, but by using sUASs, we can extend the short window of time we have during the crane migration to obtain good population estimates at ideal times.”

The estimates are used for a variety of management decisions, from setting hunting “bag limits” for the year to how refuges manage their lands and waters.

Other USGS Field Applications

The UAS Project Office and FORT are planning other diverse uses of the sUAS technology. Some of the projects in the works include:

  • identifying pygmy rabbit and sage-grouse habitat in Wyoming;
  • studying mountain pine beetle damage and extent in Colorado;
  • checking historical sage-grouse leks (mating areas) to see if they are still active;
  • locating debris piles, which provide crucial habitat for fish at various life stages, in rivers; and
  • documenting and monitoring bank erosion along a stretch of the Missouri River that borders the Lower Brule Sioux Reservation in South Dakota to determine where shoreline habitat and cultural resources are affected.

Over the course of these studies, scientists will learn which of these applications will benefit most from using drones such as the Raven A, what species can be detected with the cameras, and the efficacy of this method for aerial surveying in different environments. Many other tests are being conducted to learn how field research can be enhanced, while saving staff time and other costs, by obtaining a bird’s-eye view from a drone.

1Also called Unoccupied Aircraft Vehicles, or UAVs.

An unmanned aircraft flying above a study area.

How sUASs Work

For each specific use of sUASs, the operating pilots must first obtain a Certificate of Authorization, or "COA," from the Federal Aviation Administration (FAA) and file a flight plan. sUAS flights use aeronautical charts for mission planning just like other aircraft, and sUASs need FAA approval for night flights.

For a COA, each flight requires four trained and certified pilots: one to remotely fly the plane, one "mission controller," and two observers. The mission controller works with the software to ensure that the sUAS operations conform to both the flight plan and the stipulations of the COA. One of these stipulations is that the drones must remain in the line of sight of trained observers. Therefore, the two observers watch while the flights take place, ensuring that there is no conflict between the sUAS and other aircraft or birds flying in the area.

Pilots outfit the sUAS with either an electro-optical or an infrared camera, which is housed in the nose of the vehicle (its "payload"). The sUAS is hand-launched, whereupon the pilot uses a hand-held flight controller to view what the sUAS-mounted camera "sees" and control the Raven’s flight. Meanwhile, the mission controller monitors the flight onscreen using special software that reads geographic information system (GIS) data and monitors the global positioning system (GPS) signal given off by the aircraft. When the flight is completed, no special landing area is required; the drone is directed by the pilot to go into a deep stall and "lands" by dropping to the ground and breaking apart in an engineered way to absorb impact and protect the payload (Raven RQ-11A sUAS: USGS Training Exercise video). After landing, it is easily reassembled for its next flight.

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Date published: August 18, 2016

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