ESRL Quarterly Newsletter - Winter 2009

Airborne Lidar Catches Algae

ESRL’s Jim Churnside (Chemical Sciences Division) has used lidar instruments on airplanes to find schools of fish and squid. He’s used lidar—which bounces laser light off distant objects and captures the information-rich return signals—to find abandoned “ghost nets,” which can ensnare and kill ocean dwellers. Now, Churnside is using airborne lidar to find layers of phytoplankton—tiny plant-like creatures that are the foundation of most oceanic food chains.

This spring, Churnside and his colleagues took an unprecedented look at the progression of a phytoplankton bloom in Washington’s East Sound, by flying a remotely-controlled lidar on a small Cessna airplane over the water. Backed by ship and underwater glider data from Percy Donaghay, Jan Rines, and Jim Sullivan of the University of Rhode Island, the study provided the first on-the-ground validation that airborne lidar can detect thin layers of phytoplankton in water.

The technique could help fisheries biologists seeking to better understand fish population dynamics, Churnside said, as well as scientists trying to understand how climate change is affecting the oceans (thin layers of phytoplankton can throw affect satellite measurements of ocean dyanmics, including stratification, which are critical for understanding climate change.) The U.S. Navy, which funded part of Churnside’s research, is also interested in thin layers of plankton, which affect can acoustics and optics.

In May, Churnside’s team “watched” with lidar as a bloom of phytoplankton formed and then dissipated in East Sound. Measurements from a nearby channel captured the inflow of turbid water, as the bloom dissipated, and the lidar data captured the vertical movement of the bloom, as well. The phytoplankton dynamics were apparently related to the temperature stratification of the water, the tide, and possibly to biological factors as well, Churnside said. He reported his team’s results at the annual December meeting of the American Geophysical Union.