WWU researchers look to space to remotely detect and map snow algae

WWU graduate research assistant Colby Rand and Associate Professor of Environmental Sciences (ESCI) Alia Khan recently published a comparison of commercial small satellites, called SmallSats, and traditional satellite remote sensing technology to assess the strengths and limitations of each for mapping snow algae. 

Algae on snow and ice can reduce surface albedo — the ability to reflect light and heat — and may accelerate snow melt. Any darkening on the surface of snow or ice is akin to wearing a dark shirt on a sunny day, which will make you retain more heat than if you were wearing a light one.

The article “How commercial SmallSats are revolutionizing the remote detection and mapping of snow algae” appears in Frontiers in Remote Sensing, a journal highlighting innovation in remote sensing science. 

This work comes out of a project, Commercial Sensor Evaluation for Detection and Mapping of Snow Algae, that is funded by an award to Khan through the National Aeronautics and Space Administration (NASA).

“The presence of snow algae have a direct impact on surface darkening, which leads to enhanced melt of snow and ice,” said Khan. “Mapping the distribution of snow algae is crucial to understanding their influence on snow and ice melt, as well as their impact on the global energy balance and climate system.”

Advancements in remote sensing

Khan’s early research to map and understand snow algae relied on ground observations. More recently, her research group has begun incorporating uncrewed aerial vehicles (UAVs). 

Other studies have relied on freely available data from government-operated satellites, but the resolution has not been detailed enough to effectively measure and track the algal blooms at a fine-scale. 

Advances in satellite technology in recent years, including the emergence of SmallSats, are giving researchers access to more and better information. 

“The high spatial resolution of the SmallSats enables more accurate detection of the presence of snow algae in remote regions of the cryosphere that are difficult to access by foot,” said Khan.

SmallSats are smaller, lighter, and less expensive to design, build, and deploy. They are often launched in constellations where multiple satellites work together to monitor specific regions over time.

NASA’s Commercial SmallSat Data Acquisition (CSDA) program obtains and provides access to commercial satellite imagery. 

“NASA’s CSDA data allowed us to monitor snow algae in remote and inaccessible areas without the need for field visits, enabling long-term observation of changes over time,” said Rand, who plans to graduate in this summer with a master’s degree in Environmental Science.

The use of UAVs in remote sensing to provide high-resolution images has also grown in recent years, but in some places – including much of Mt. Baker, which lies within federally designated wilderness areas – drone use is prohibited. 

In practice, researchers may, by choice or necessity, combine various technologies and techniques. The use of high-resolution drone imagery can provide additional detail and help to validate data from other sources

Working with SmallSat imagery does have a few downsides. One key limitation of SmallSats is their relatively small image footprints, making it impossible to capture imagery of certain areas, such as the entirety of Mt. Baker, in a single scene. 

Another is that the data requires new or adapted methods of analysis due to differences in spectral bands and resolution from different platforms.

Mapping snow algae, pixel by pixel

For this article, Rand and Khan compared imagery from SmallSats such as PlanetScope, SkySat, and BlackSky to those from traditional satellites like WorldView, Sentinel-2, and Landsat. Each satellite platform varies in spatial resolution, spectral coverage, and revisit frequency.

They applied various image classification techniques, including spectral indices, to map the location of snow algae over time on Mt. Baker. Scientists use spectral indexing to measure vegetation health and moisture levels and, more recently, algae blooms on snow, ice, and water.

According to Rand, spectral indices are mathematical formulas used to classify satellite and drone images on a per-pixel basis. 

“Each pixel captures surface reflectance across several intervals of the electromagnetic spectrum, and these values are used to determine whether a pixel represents algae-covered or ‘clean’ snow,” he said. More resolution means more detail and better accuracy.

SmallSats show potential to transform remote sensing research

Despite a few limitations, commercial SmallSats provide new opportunities for mapping snow algae at finer scales and higher revisit frequencies than previously possible with traditional government-funded satellites. 

“The incredible coverage of the new small-sat imaging sensors — covering most areas on earth multiple times per day — is completely transforming this kind of environmental monitoring,” said Ted Scambos, senior research scientist at the University of Colorado Boulder’s Cooperative Institute for Research in the Environmental Sciences (CIRES).

For climate researchers like Khan, this is the technology they’ve been waiting for.

“I have been studying snow algae ‘on the ground’ since 2018,” said Khan. “In the past, we relied on ground-based and airborne measurements with a UAV because these ephemeral snow algae blooms were beyond the detection capabilities of satellite imaging at the required scale. However, being able to track snow algae blooms at 50 cm resolution from space is a game-changer.”  

Learn more about Environmental Sciences degrees and programs on the College of the Environment website. 

Jennifer Nerad covers Western's College of the Environment for the Office of University Communications. Have a great story idea? Reach out to her at neradj@wwu.edu.