Historically, air content in laboratory flumes was measured using expensive fine scale probes based on hot wire, electrical conductivity, pitot tubes, or optical technologies. These methods are expensive and extremely difficult to modify for use in the field. Consequently, we developed an approach to measure air content using Time Domain Reflectometry (TDR), which is highly robust in the field and one-tenth the cost of traditional methods. According to the TDR approach, the highly different dielectric constants of air and water determine the transit time of a voltage pulse traveling along parallel rods. The number of pulses each second is recorded. To convert pulse data to air content, an empirical calibration between the two is needed.The calibration should account for ambient temperature and water salinity. Below are photos and a schematic of the TDR sensor from Campbell Scientific that we used in our early research. Other companies now also sell such technology.
- Air Content Measurements -
Lab Methods - Single
Phase Test Results - Air-Water Mixture
Calibrations - Turbulent Air-Water
Mixture Time Series
Field Methods - Field Site - Field Results
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