CAMEX-3 JPL Surface Acoustic Wave (SAW) Hygrometer

Developed at the Jet Propulsion Laboratory (JPL), this hygrometer uses a custom made surface acoustic wave (SAW) device as a sensitive detector of condensation in lieu of the more traditional chilled mirror and light beam approach. The SAW device is a quartz crystal designed to support high-frequency acoustic oscillations. Because these oscillations are quite sensitive to surface effects, condensation produces a measurable shift in the resonance frequency of the SAW device. A two-stage TEC electronically heats or cools the SAW device, while a platinum resistor (thermistor) is used to monitor the temperature. The SAW hygrometer measures dewpoint by establishing equilibrium between evaporation and condensation on the surface of the SAW device. Using a SAW device as a fast, high-sensitivity moisture sensor, a feedback controller measures the condensation on the sensor surface, and responds by heating or cooling the sensor to maintain equilibrium. The equilibrium temperature under feedback control is a measure of dewpoint or frostpoint, depending on the phase of the condensed moisture.

The JPL SAW hygrometer flew aboard the NASA DC-8 aircraft during the third field campaign of the Convection and Moisture Experiment (CAMEX-3). CAMEX-3 was based out of Patrick Air Force Base, Florida from 6 August - 23 September, 1998 and successfully studied Hurricanes Bonnie, Danielle, Earl and Georges. CAMEX-3 collected data for research in tropical cyclone development, tracking, intensification, and landfalling impacts using NASA-funded aircraft and surface remote sensing instrumentation.

(START DATE: 1998-08-06 STOP DATE: 1998-09-23)

NASA Information Contact: Michael Goodman, Global Hydrology and Climate Center
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