Subsurface measurement needs for ecological, hydrological and agricultural applications

Biological activities occurring in the subsurface largely depend on the relative abundances of water and oxygen that are required for respiration. Accurate measurements of soil water content and flux in addition to concentrations of CO₂ and O₂ have been the target of research to improve agriculture and environmental management. The majority of sensors used for subsurface science are based on electrical, electromagnetic or optical measurement principles. Novel developments in subsurface water-related measurement approaches include on-the-go time domain reflectometry (TDR) probes and heat-pulse-based water flux probes. Measurement approaches for gas concentration and flux have relied on new developments using thin films and optical techniques, while gas flux measurements utilize surface chamber measurements and subsurface concentration gradient approaches.