No abstract

The National Oceanic and Atmospheric Administration (NOAA) is transitioning the primary water level sensor at the majority of tide stations in the National Water Level Observation Network (NWLON) from an acoustic ranging system to a microwave radar system. Field comparison of the acoustic and microwave systems finds statistically equivalent performance when temperature gradients between the acoustic sensor and water surface are small and when significant wave height is less than roughly 0.5 m. When significant wave height is greater than approximately 0.5–1 m, the acoustic system consistently reports lower water levels. An analysis of 2 months of acoustic and microwave water level data at Duck, North Carolina, finds that the majority of differences between the two sensors can be attributed to systemic errors in the acoustic system and that the microwave system captures water level variability with higher fidelity than the acoustic system. NWLON real-time data products include the water level standard deviation, a statistic that can serve as a proxy for significant wave height. This study identifies 29 coastal water level stations that are candidates for monitoring wave height based on water level standard deviation, potentially adding a significant source of data for the sparsely sampled coastal wave fields around the United States, and finds that the microwave sensor is better suited than the acoustic system for wave height estimates.

Abstract. An empirical fetch-limited ocean wave spectrum has been combined with an acoustic ray-based model to predict the acoustic signal time-angle fluctuations induced by sea surface roughness. Rough sea surface realizations are generated and used as sea surface boundaries with the acoustic model. To validate this model, results are compared against experimental data collected in a fetch limited region. These data includes simultaneous wind speed and acoustic propagation (1-18 kHz) measurements in a fetch limited coastal region. Modeled time-angle fluctuations compare well with field data at lower wind speeds (< 10 m/s).