River & Estuary Observation Network: Refinement of Stage Height Sensor Subsystem for Low Cost and High Reliability

Abstract

A system comprised of software and on-site measurements is presented for accurately obtaining water stage data from vented or non-vented submersible pressure sensors installed at autonomous stream gauging stations. The system accounts for pressure sensor offset errors, water density, and local gravitational acceleration to produce a stage height reading which is accurate to either ±0.01 ft (±3 mm) or to the accuracy limit of the sensor, whichever is greater. A 2nd order polynomial expression for determination of water density from temperature and salinity is developed and found to be sufficiently accurate for this purpose. Simulated stage measurements performed in the laboratory with a commercially produced sensor showed errors of up to ±0.04 ft in reported stage when the sensor’s default conversion from pressure to depth was used; the maximum error limit was reduced to ±0.02 ft when the sensor output was instead processed using the new system. A custom-designed, low-cost, versatile submersible pressure sensor is introduced and tested under the same conditions and found to exhibit a maximum error of ±0.04 ft without any sensor calibration. These new developments, integrated into previously developed inexpensive base stations, enable accurate monitoring of stage height at remote locations with low installation and operating costs.

Keywords: depth sensor, gage height, hydrologic monitoring, hydrology, level sensor, stage height, streamflow, water surface elevat ion