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Stitching Together the Data Quilt

Building a map from the mountaintops to the beaches to the ocean floor.
April 13, 2017

Waves roll over the flat expanse of West Beach on Calvert Island. Seaweed, caught in the surf, accumulates over a kilometer of white sand in dark squishy piles. Trees, insects, and mammals are all enriched by the nutrients associated with these heaps of decay. A team of ecologists is trying to trace how much seaweed tumbles onshore every year and where those nutrients are ending up. But first they need maps—of everything.

“Terrestrial maps end at the high tide line and hydrographic charts provide only very general descriptions of shorelines. The intertidal zone, which can range up to fourteen feet [roughly 4 meters] on the Central Coast, is this big missing chunk of topographical information,” says Sara Wickham, a Hakai scholar and master’s student at the University of Victoria.

To ensure that researchers have a clear image of that critical area at the intersection of land and sea, Hakai Institute’s geospatial technologies team is combining their collective mapping efforts above and below the water using a technique called Integrated Terrain Modeling. Integrated Terrain Modeling stitches together detailed maps of the land, intertidal, and seafloor into a single image of the coast.

The land and the ocean are connected, so we dont want to look at ecosystem processes on land or in the ocean in silos. Anybody interested in the coastal margin and how ecosystems interact with each other would benefit from these integrated maps, says Hakai scientist Derek Heathfield.

Integrated Terrain Modeling combines data from LiDAR, drones, and sonar to create one single image of the coast from mountaintop to ocean floor. Figure by Mark Garrison

On land, Hakai scientists use LiDAR to map both the elevation of the ground and the height of the tree canopy. Often deployed from an airplane, LiDAR measures the time it takes for laser pulses to hit an object on the ground and bounce back. That same concept can be used at sea. But when it hits the water light is absorbed and diffracts, so we can’t use lasers underwater. Instead, we use sound.

A multi-beam echosounder creates a map by emiting sound pulses that travel from a boat at the ocean’s surface down to the seafloor before bouncing back. Rather than finding enemy submarines, this sonar-like system calculates the distance to the seafloor or nearest underwater vegetation to create a map of the bottom.

The challenge starts at the acquisition of these data. We try to fly the LiDAR at the lowest tide possible and do the sonar underwater at the highest tide possible. But its that point of overlap thats critical to piece the data together,” says Heathfield.

Thats where drones come in. Photos taken from the drone are combined using software into a highly accurate picture of the area between the forests and the seafloor—the intertidal and shorelines.

A three-dimensional point cloud representation of changes to sand dunes on Calvert Island over one year. These images were made by combining thousands of photos taken from a drone. Photos by Derek Heathfield

Each of the three mapping methods creates millions of data points. Each corresponds to a precise elevation and they create a three-dimensional landscape when blended together onto one map. Scientists can now explore the whole landscape from mountaintop to ocean floor to study those critical connections between the land and the sea. Maps will never be the same.