Using Lasers to Map in Glorious Detail

Hakai Institute scientists working on the Central Coast of British Columbia, from archaeologists to forest ecologists, need high-quality maps of what ecosystems cover the islands. But islands in this part of BC are covered by impassable terrain—boot-snatching bogs, impenetrable thickets of salal bushes, and shifty sand dunes.

Calvert Island and its neighbor, Hecate Island, together make up an area larger than the city of Montreal. Mapping it the conventional way, on foot, would be nearly impossible. High-tech strategies, such as aerial photos, are better, but still limited. Hakai researchers have spent the last four years taking it to the next level: lasers.

Scanning the Earth from satellites or aircraft is called remote sensing. Using remote sensing, geographers can cover a much larger area compared to ground-based mapping, and these maps can in turn help plan more in-depth studies, determine how many trees are on the landscape, or quantify how much of each type of ecosystem covers the region.

“Remote sensing offers almost an infinite number of possibilities to what you can measure,” says Hakai Institute researcher Ian Giesbrecht.

Even with aerial help, two-dimensional maps are somewhat limited. Historically, geographers classified terrestrial ecosystems by examining aerial photos taken from a plane. But the resulting map contains minimal information about the three-dimensional structure of the vegetation, which is an important measurement considered by forest scientists. That is where the lasers come in. LiDAR, a portmanteau of light and radar, is a technique that uses a laser scanner attached to a plane.

Much like its slower cousin, the sound-based sonar, LiDAR uses a light pulse that bounces off the object it’s trying to image. A laser shoots pulses downward and the light bounces off vegetation and land masses before returning to the plane-bound scanner. A three-dimensional image can then be created with vegetation either present, or removed to show the underlying geological structure of the land.

Compared to aerial photos, LiDAR maps can rapidly classify landscapes into their respective ecosystems by quantitatively identifying repeating patterns with high resolution.

“These methods give much finer detail compared to aerial photos alone. We were the first to produce LiDAR ecosystem maps on the British Columbia outer coast,” says Giesbrecht.

Shanley Thompson, who recently obtained her PhD from the University of Victoria, led a collaborative effort between the Hakai Institute, UVic, and the BC Ministry of Forests, Lands, and Natural Resource Operations. Their multi-year effort paid off, and highly detailed ecosystem classification maps of Calvert and Hecate Islands were recently published in the scientific journal Applied Geography.

These maps can now be used across a wide variety of projects. For instance, we can now track the amount of carbon coming off the land from specific ecosystems and into the ocean, which provides food for the base of the ocean food web.

“We would love to get these detailed maps for other parts of the coast, too,” adds Giesbrecht.

A copy of Thompson et al. (2016) in Applied Geography can be found here. An interactive version of the LiDAR ecosystem classification map with metadata can be found here.