Drone keeping an eye on Elkhorn Slough

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A drone buzzes above Elkhorn Slough, zipping back and forth in an elongated zig-zag pattern. As it glides through the air, it takes snapshots of the surface to monitor plant life and ground elevation.

Surveying the land by drone is a technique being used to track Hester Marsh’s delicate restoration, an ongoing project since 2017.

Historically, the marshland was diked and drained to create pastures, causing the sponge-like land to shrink. Now, scientists are piling on dirt and restoring native plants to revive the salt marsh to its former glory. They’re also elevating it to counteract future sea-level rise caused by climate change.

John Haskins points out the drone’s flight path on the device’s remote control. (McKenzie Prillaman — Herald Correspondent) 

But that’s a tricky feat with such a finicky ecosystem.

Ensuring the marsh is thriving and healthy requires frequent and accurate monitoring, which can take hours of labor spent in the mud. Data collection by drone, however, makes the process faster and more precise than ever.

“The marsh itself is like Goldilocks,” said John Haskins, water quality monitoring specialist of the Elkhorn Slough National Estuarine Research Reserve and co-lead of the drone project. “It wants to be in a perfect zone of the tidal frame to be able to grow.”

If the marsh is too high, it doesn’t receive enough water for plant growth. But if it’s too low, flooding kills the plants. The sweet spot, Haskins explained, exists within a 3-foot region inside of the 8-foot tidal frame, the full range that the ocean tides can reach on the U.S. West Coast.

Traditionally, scientists examine how vegetation is faring by hand. Using meter sticks and tape measures, they count the number of each plant type within a small area and calculate approximate vegetation coverage throughout the entire region.

Drone landing after flying over the phase II area of Hester Marsh’s restoration. (McKenzie Prillaman — Herald Correspondent) 

The stark-white foot-long drone, however, with its two affixed cameras, can survey the entire 35-acre area of Hester Marsh’s phase II restoration in about 45 minutes. Further, a snapshot of the entire region means precise plant counts rather than estimations.

“What we discovered is that for a restoration project like this, where there’s not a lot of vegetation here now, it’s a really quick and easy way to monitor change through time,” said Charlie Endris, research scientist and GIS specialist of the Moss Landing Marine Laboratories and co-lead of the drone project.

While flying, one of the drone’s cameras captures nearly 1,000 images that are later stitched together to create a three-dimensional elevation map of the entire region. The other takes pictures with two wavelengths of light invisible to the human eye that help identify specific plant varieties in the marsh.

In the comfort of his office, Haskins plugs in an aerial map of Hester Marsh into an app. He then draws out a flight path for the drone, where it sweeps back and forth across the land, ensuring that the images will overlap so they can be pieced together later.

After driving out to the marsh, Haskins unloads the drone, which he has a special pilot license to operate, and sends it instructions through the app. He and Endris first thought of monitoring the marsh by drone in 2015, when they came out to the slough with someone flying a fixed-wing drone, essentially a miniature airplane.

Haskins’s drone takes off and automatically follows the route laid out earlier. The device glides 50 meters above the ground, taking pictures every couple of seconds all while detecting and avoiding other airborne objects, like birds. It returns to the landing pad about every 15 minutes for fresh batteries.

When the flight is finished and the drone is back at the office, Haskins and Endris process “gigabytes and gigabytes” of data collected by the drone. It takes days to convert all of the images into a product that can be interpreted, Endris said. Sometimes he and Haskins get help from local university students, but the duo is looking for a way to upload the data online and turn it into a community science project.

The final result is a three-dimensional elevation model with centimeter-level precision categorized into different zones, such as vegetated marsh, non-vegetated marsh and grasslands. Using this tool, scientists at Elkhorn Slough can tell how much the piled-on sediment gets compressed over time, assess the plant varieties and locations, track creek formation and development and more.

Charlie Endris (left) and John Haskins (right) holding a drone used to survey Elkhorn Slough. (McKenzie Prillaman — Herald Correspondent) 

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