Hacking a Climate Satellite to See Beneath the Ocean's Surface

When NASA launched its CALIPSO spacecraft, the space agency did not intend to estimate phytoplankton populations.

NASA’s Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite can be repurposed to measure phytoplankton blooms like this one to help estimate the ocean’s global carbon stock. Credit: NASA Goddard, CC BY 2.0

By Eric Betz 27 May 2015

NASA launched its Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission in 2006 to study the impact of clouds in the atmosphere. The climate satellite uses lidar, which shoots laser light pulses at Earth’s surface and measures how they bounce back to measure the distance to objects below. The space agency’s goal is to combine that information with data from other satellites to show vertical structures, water content in clouds, and other climate indicators.

Global distributions of surface particulate particulate organic carbon from CALIPSO lidar measurements Credit: Supplementary Materials, Behrenfeld et al. [2013] — Global distributions of surface particulate organic carbon from CALIPSO lidar measurements. Credit: Supplementary Materials, *Behrenfeld et al.* [2013]

Lidar is not a new tool for ocean research. Scientists have used it to profile schools of fish and ocean surface roughness and even to detect waves by interpreting phytoplankton signatures. Recent studies found that CALIPSO is also capable of capturing data from below the surface of the ocean. In 2008, a pair of researchers compared CALIPSO data taken before and after Cyclone Nargis to show how the storm vertically mixed sediments. More recently, scientists also showed the spacecraft had potential to estimate the global carbon stocks in Earth’s oceans.

Lu et al. wanted to estimate exactly how much subsurface backscatter they could pick up from the spacecraft’s lidar measurements to more precisely determine its usefulness.

First, the team had to remove the signals they did not need from the lidar observations. Once that was accomplished, the backscatter signal showed significant correlations with chlorophyll a concentrations, an indicator of phytoplankton presence. They also found the signal was sufficient to estimate particulate organic carbon, a combination of living and dead organic material. The researchers say the two measurements taken together would allow scientists to calculate the ocean’s global carbon stock. (Journal of Geophysical Research: Oceans, doi:10.1002/2014JC009970, 2014)

—Eric Betz, Freelance writer

Citation: Betz, E. (2015), Hacking a climate satellite to see beneath the ocean’s surface, Eos, 96, doi:10.1029/2015EO030183. Published on 27 May 2015.