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Keeping a digital eye on Canada’s wetlands
When you sign on to map all of Canada’s forests, lakes and wetlands, the sheer numbers will tell you you’re signing on for a life’s work. Mike Wulder, a Senior Research Scientist at Natural Resources Canada, has done exactly that.
“In general, within Canada, the national land base is about a billion hectares,” Wulder says, matter-of-factly. “Of that, we’re looking at the forested area of Canada. So, if you net out the agricultural areas in the south and the more tundra and Arctic areas in the north, you end up with about 65 per cent of the country, or 650 million hectares.”
Within that area, you find trees, lakes and wetlands — “the types of things you want to see when you go camping,” he says. He’s responsible for trying to generate information about those areas so the country has maps of it, and scientists can see an assess its status and changes.
“Working for the Pacific Forestry Centre, it’s no surprise that mapping the forest is one of the main focuses,” he says with a laugh.
But it’s a huge area and he wants to be able to map it with a high level of detail, which has, in the past, created a bit of a conundrum because he needed high spatial detail over a large area.
“The way we used to tackle it was usually through sampling,” he says. “So you’d work with statisticians and they’d help you design a system by which you could rigorously represent this large area with samples.”
While samples enable reporting, maps are also useful to many users, so he started seeking ways to make maps and has been using satellite data. In 2008, the U.S. Geological Survey opened up its Landsat archives, which meant there was a dataset available to him and his team to make not only maps, but to make many maps over time.
“That’s meant being able to revisit a lot of our monitoring and reporting activities by using this dataset available to us through free and open access,” he says.
Following some initial and highly successful mapping with the newly discovered information, recently the team decided to take it one step further and look at wetlands. A new paper, titled A National Assessment of Wetland Status and Trends for Canada’s Forested Ecosystems Using 33 Years of Earth Observation Satellite Data, looks at this “dynamic category,” so named because they tend to change frequently over time. Many land cover classes are quite stable, but wetlands are more of a land condition, changing within and between years.
“This is the fun part from my point of view,” Wulder says. “It’s the whole idea that we have 33 years or more worth of satellite data that we’ve been able to access from open access. Each of these images covers 185 kilometres, so you need minimum 1,200 of them to cover the entire country for a single year. Then you have cloud, smoke, haze — anything that can lead to missed data — so you need to come up with processing steps that allow you to remove these artifacts, obtain more imagery, and make the complete coverage so you can make these annual maps.”
It may be fun, but it’s not simple. He says he has to do all kinds of processing with the dataset to get the digital numbers to be such that he can use in them in algorithms. After that, he can map.
“Now that we’re able look at this land-cover, it’s no longer a single-year map; we can use the year-on-year information to self-inform through time so you can see that you have logical transitions from year to year,” he says. “Then, we wondered if we had more information to see whether certain places were wetland or not and how these areas interacted with forests. The paper looks at how frequently a given location is mapped as wetlands through time.
To pull all of this off, he uses high-powered computing, provided by Compute Canada.
“You have all these images to deal with and you need quite a bit of storage and processing capacity for them,” he says. “We collaborate closely with academics at UBC and this allows for student training and access to highly qualified professionals that are working as students or post-docs. Without Compute Canada, we wouldn’t have the shared working environment and the collegial process we’ve been able to follow. Compute Canada helps us incubate and accelerate our science activity.”
When it comes to societal benefits, the projects give people such as Wulder a baseline understanding of the state of wetlands that he can then compare to past years or make projections for future conditions. More broadly, the information can be used by provincial, national and local governments for insights on wetland status and trends. And the satellite-derived information Wulder and his team have produced is informing Canada’s National Forest Inventory and carbon accounting activities, as well as much science. It might be helpful, for example, in looking at how harvesting has changed over the past three decades; or, how well trees are regenerating after disturbances.
The private sector, meanwhile, can download and use these wetland datasets to help plan where to put power lines and roads. The maps will tell them whether their infrastructure will be going through a wetland, for example.
This work is supported by the Climate Change Impact and Ecosystem Resilience (CCIER) program of the Canadian Space Agency and is enriched through collaboration with the Integrated Remote Sensing Studio within the Faculty of Forestry at the University of British Columbia.