Scientists have taken the concept of remote sensing to an entirely new level, using lidar to peer into the depths of the ocean. The new technique allows the experts to study algae and ocean composition much farther down in the sea than what has been possible using satellite sensors.
Study co-author Barney Balch is a senior research scientist at the Bigelow Laboratory for Ocean Sciences.
“Traditional satellite remote sensing approaches can collect a wide range of information about the upper ocean, but satellites typically can’t ‘see’ deeper than the top five or 10 meters of the sea,” said Balch. “Harnessing a tool that lets us look so much deeper into the ocean is like having a new set of eyes.”
Lidar detects and measures the distance to reflective particles like algae in the ocean by illuminating them with laser light. On a research expedition in 2018, study lead author Brian Collister tested the ability of a shipboard lidar system to detect algae and other particles in the deep ocean.
“The lidar approach has the potential to fill some important gaps in our ability to measure ocean biology from space,” said Collister, who is a PhD student at Old Dominion University. “This technique will shed new light on the distribution of biology in the upper oceans, and allow us to better understand their role in Earth’s climate.”
Balch’s research team has studied the Gulf of Maine for over two decades. The scientists’ experience in finding and identifying algae in this ecosystem provided key knowledge for testing out the lidar system in this area.
The team used lidar to detect and measure particles of the mineral calcium carbonate, and collect information about a bloom of coccolithophores. These algae surround themselves with calcium carbonate plates, which are white in color and highly reflective. This particular coccolithophore bloom turned out to be the largest observed in the region in 30 years.
“This cruise allowed us an ideal opportunity to try the lidar system out with the ability to sample the water and know exactly what species were in it,” said Balch. “Lidar has been used in the ocean for decades, but few, if any, studies have been done inside a confirmed coccolithophore bloom, which profoundly changes how light behaves in the environment.”
Located throughout the ocean worldwide, coccolithophores have a major influence on the biogeochemical cycles that shape the planet, and studying the algae is key to understanding global ocean dynamics.
The new research suggests that lidar will make it possible to estimate coccolithophore populations remotely, which could save a lot of time and money that is typically used for field studies.
“It’s a huge deal that we are learning to reliably identify particles in the ocean from a lidar system positioned above the water,” said study co-author Richard Zimmerman. “This is a significant advance, and it could revolutionize our ability to characterize and model marine ecosystems.”
The study is published in the journal Applied Optics.