Noisy Wave Data Smoothing with B-Splines

Water surface elevation, η(t), is often measured in marine field experiments and research facilities with echo ranging gauges. Proper operation of these gauges requires judicious setting of the receiver circuit to prevent data drop-outs. Field experiments, where the sensors are left unattended for long periods of time, are particularly susceptible of data drop-outs as metocean conditions affect the reception of the echo signal or the pre-selected range of measurement changes. When the amount of data collected is small, user interactive software featuring simple interpolation methods allows for replacing data drop-outs relatively quickly. However, these are slow when the amount of data collected is large. An automated data smoothing method has been developed implementing B-splines. The software derived from this implementation was tested for accuracy using random wave records measured during experiments at the O.H. Hinsdale Wave Research Laboratory at Oregon State University. In the experiments, η(t) was recorded with two ultrasonic wave gauges. One was carefully set to record realizations free of data drop-outs and to be used as targets. The other gauge, not so carefully set, recorded data with drop-outs that were smoothed using a) a user interactive software and b) the automated software. The data "drop-out free" records obtained after smoothing were compared to the target records by means of cross correlation analysis. Records smoothed with the automated software showed the same or better correlation to their corresponding data "drop-out free" records than records smoothed with a user interactive software by visual inspection.