US: Scientists at NASA's Jet Propulsion Laboratory, California, and the U.S. Geological Survey have successfully demonstrated how a NASA-developed airborne environmental monitoring instrument can be applied to help water managers monitor water quality in San Francisco Bay, and other inland and coastal water bodies around the world.
In a study published in the current issue of the journal Environmental Science & Technology, researchers combined water sample measurements collected by USGS scientists aboard a high-speed boat in northeastern San Francisco Bay with data collected by JPL scientists at the same time onboard a specially instrumented Twin Otter aircraft flying overhead.
The plane carried the JPL-developed Portable Remote Imaging Spectrometer (PRISM), which measures the amount and wavelength of visible light and near-infrared radiation reflected toward the instrument from the water below. The PRISM data allow researchers to detect the unique spectral signatures of several water constituents typically used as indicators of water quality.
When the two data sets were later analyzed and compared in laboratories, the PRISM data closely matched the water quality information collected from the boat. The benefit of PRISM is that it can greatly expand the spatial coverage of traditional boat- and fixed-monitoring, station-based approaches used for water quality monitoring.
For this study, the researchers analyzed turbidity (how cloudy the water is), chlorophyll-a (an indicator of phytoplankton in the water), dissolved organic carbon (a source of undesired disinfection by-products produced during the treatment of drinking water), and sediments suspended in the water.
Dissolved organic carbon is also a useful indicator of the amount of dissolved methylmercury, a potent neurotoxin that tends to accumulate in fish and other wildlife in the San Francisco Bay-Delta Estuary. The experiment demonstrated how a single image from PRISM can instantaneously provide a detailed snapshot of these important water quality indicators over a large and diverse water body.
New imaging spectrometers like PRISM can enable accurate detection of water quality indicators that were previously difficult to measure using existing satellite sensors. Scientists hope to apply the PRISM technology to sensors on future Earth-orbiting satellites that can provide continuous global monitoring.
"This study successfully demonstrated the potential of remote sensing to monitor water quality indicators and their variability in the San Francisco Bay-Delta Estuary—one of California's most important water resources—where wetland restoration, human activities and climate change can impact water quality and ecosystem productivity," said study lead author Cédric G. Fichot, a JPL postdoctoral researcher.