Error analysis of water level measured from a bottom mounted ocean platform

The U.S. NOAA National Ocean Service Center for Operational Oceanographic Products and Services (CO-OPS) has been pursuing an effort to develop and test a real-time oceanographic and meteorological observing system, named “The Hermit,” for collection and transmission of real-time measurements at remote coastal sites with limited infrastructure. One of The Hermit's primary sensors is a conductivity, temperature, pressure sensor (CTP), for measuring water level. The CTP sensor is mounted onto a platform that is lowered to the seabed and left for a period of 90 days or longer. The identification of potential sources of water level measurement error from this system is critical in mitigating errors in final data products. Additionally, because of the broad range of CO-OPS' water level data applications, identifying measurement error sources is critical for assessing the applications for which a new measurement system type may or may not be suitable. This paper presents and evaluates four sources of water level measurement error associated with bottom mounted pressure sensors: long-term sensor drift, vertically referencing water level, biofouling, and platform settling.