Tahoe buoys are mini-research labs
August 30, 2005
Scientists from NASA’s Jet Propulsion Laboratory and the University of California, Davis, have placed a network of research buoys and rafts on Lake Tahoe. Serving as research stations, these vessels provide information that ensures Earth-observing satellites are measuring the Earth’s surface temperature correctly. Several environmental satellites, including Terra, Landsat, Aqua and Envisat, fly over Lake Tahoe to collect data, with about six satellites passing by each day.
The NASA and UC Davis scientists have been collaborating to collect data on Lake Tahoe and to validate the data gathered by the environmental satellites since 1999. Initially, four rafts were deployed, until Tahoe’s harsh conditions required use of buoys that are more robust. UC Davis researchers used various parts of the broken rafts to make two new rafts, which were deployed in the southern part of the lake. There are now six research stations on Lake Tahoe.
Temperature data from the research stations can be field-tested for accuracy and compared to the satellites’ measurements for calibration. These validated NASA satellites collect temperature data, which are used for a variety of purposes, such as creating surface-temperature maps used in weather forecasting, as often seen on The Weather Channel.
NASA scientists selected Lake Tahoe as a validation site just before the Terra satellite was launched on a 15-year mission to study Earth’s environment in 1999. “Water is the best natural target for validating thermal infrared measurements,” says Simon Hook, Ph.D., who runs the Lake Tahoe validation site. Lake Tahoe provides an especially good location for calibration because the water surface is large; the lake never freezes; freshwater is easier on the equipment; and the high elevation and usually clear days reduce the amount of atmospheric interference.
Hook works on JPL’s Advanced Spaceborne Thermal Emission and Reflection Radiometer, one of five instruments on the satellite, Terra. ASTER views Earth with 14 spectral bands, from the visible to the thermal infrared. The instrument’s visible bands produce high-resolution images of Earth’s surface and clouds. The thermal infrared bands provide temperature measurements, making it possible for ASTER to spot the signs that a dormant volcano may be awakening, or see that warm water is collecting on one side of Lake Tahoe while cold water is rising on the opposite shore.
These research stations are the only permanently moored objects on the lake and each is a mini-research laboratory. Each has a radiometer that can measure the lake’s surface skin temperature to within 0.05 of a degree; a temperature sensor trailing in the water that measures the lake’s temperature at depth; and meteorological equipment that determines air temperature, wind speed and direction, pressure, relative humidity, and net radiation.
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The research stations seem to be continually growing, as more equipment is added. For example, California’s Air Resources Board recently added an air sampler to the stations, and the UC Davis Tahoe Environmental Research Center has put on a deposition sampler to see what is coming into the lake from the air. The deposition sampler enables scientists to measure the amount of nitrogen and dust falling into the lake from the atmosphere.
The data collected from these stations have multiple uses. UC Davis researchers are investigating lake circulation, clarity loss and other environmental changes. Geoff Schladow, who has been studying Lake Tahoe for the last eight years, notes that, “Too many nutrients in the water were once thought to be a problem, but in the past few years we started finding that fine sediment has a larger effect on clarity.” The satellite data enable Schladow and his colleagues to see temperature changes across the entire lake, making it possible to understand lake circulation and its effect on the transport of fine particles.
Data from the buoy stations and satellites will enable graduate students and researchers to study the physical processes that contribute to Lake Tahoe’s unique clarity and build computer models to categorize and understand these processes.
Using the data, students can build their own models in the classroom, and see firsthand the dynamic conditions that exist in these subalpine environments.
The public can also view the data online at http://terc.ucdavis.edu or http://laketahoe.jpl.nasa.gov. These Web sites provide access to some of the near-real time data acquired from the monitoring stations. The Coast Guard and other boaters can check lake conditions, such as wind speed, air temperature and water temperature, to determine which gear to wear, for example. This online information is updated at least hourly.
The mutual benefits of this research program for the space scientists, our local scientists, students, and the public make the research buoys a good example of the kind of collaborative projects that federal, state, and local officials promote for solving Tahoe’s environmental problems.