The Standing Wave (ADR) Measurement Principle
Standing Wave, or Amplitude Domain Reflectometry (ADR), uses an oscillator to generate an electromagnetic wave at a consistent frequency, which is transmitted through a central signal rod, using outer rods as an electrical shield. The electromagnetic wave is partially reflected by areas of the medium with different dielectric constants (water content), producing a measurable voltage standing wave. ADR measures volumetric soil water (VSW%) independently of all other soil variables, including density, texture, temperature and electrical conductivity. ADR does not require in-situ calibration to accurately measure Volumetric Soil Water (VSW%).
Environmental, agriculture & engineering applications requiring assessment of the changes of soil moisture in absolute mm and the exact volumetric soil moisture use ADR or TDR technologies. ADR sensors that have been buried permanently in landfills are still functioning after 15+ years.