A Comparison of Datums Derived from CO-OPS Verified Data Products and Tidal Analysis Datum Calculator.

Abstract

The NOAA National Ocean Service Center for Operational Oceanographic Products and Services (CO-OPS) has developed a publicly accessible tool to compute tidal datums from water level data with a variety of tidal signals. The Tidal Analysis and Datums Calculator (TAD) uses a Butterworth digital filter to remove high frequency (> 4 cycles/day) water level variability in order to identify tidal high and low waters from observed water level data. Present CO-OPS procedure uses a Curve Fit Manual Verification (CFMV) approach to identify tidal high and low waters. A comparison of high and low water selections at eight long-term NOAA water level stations shows that the mean difference between selections made by TAD and CFMV have a mean bias of 0 at the 1 mm level, and the standard deviations of the differences are all within CO-OPSaccepted data processing error bounds. Instances of major differences (> 0.02 m) between individual high and low water selections are rare and have no significant influence on the resulting datums. The difference in errors associated with tidal datums computed by TAD and CFMV is less than 0.002 m when compared to the published tidal datums at the eight stations. The results here demonstrate that TAD is able to efficiently determine accurate high and low water values without manual verification. Therefore, users of this new tool will be able to generate consistent and reproducible tidal datums that are useful for coastal planning and restoration.