Development of a laser-based water level sensor for fine-scale ecohydrological measurements

Evapotranspiration (ET) is a critical component of the global water cycle, but one that is difficult to estimate due in part to a lack of accurate and affordable sensor technology. One low-cost approach to measuring site-specific ET in areas where the water table is close to the surface is to take advantage of the diurnal fluctuations in surface water and groundwater driven by ET. This method requires highly sensitive measurement to accurately quantify water table variation. The goal of this work is to develop and test a laser-based water level sensor (LB-WLS) to improve the estimate of ET via diurnal variations in water level. The LB-WLS was compared against traditional total pressure transducers (TPT) in both laboratory and remote settings. The LB-WLS was found to have lower residual noise, with an average Root Square Error (RSE) of 0.05±0.04 cm, compared to 0.19±0.16 cm for the TPT sensor. While sensor development is ongoing, this level of performance represents a major improvement in fine-scale monitoring of surface water and groundwater.