O NLINE TIDAL DATUM COMPUTATIONS

JOA Surveys, LLC, Anchorage, Alaska www.joasurveys.com [email protected] 907-561-0136

Tide Data and an Email Address

JOA Surveys, LLC has developed a simple web service for computing National Tidal Datum Epoch equivalent tidal datums from user collected water level data. The user submits water level data series in a comma delimited text file along with their email address, and can optionally select a control tide station. The online service will process data recorded at sample rates from 1 second to 1 hour. The web service will email the user the computed tidal datums and graphs that allow basic quality review.

NOAA CO-OPS Methodology from 30 locations where water level data and tidal datums are published by NOAA CO-OPS. The web service runs a collection of Octave scripts The locations were distributed from the Alaskan that smooth the raw data using an adaptive Arctic to Puerto Rico and represent a lowpass Butterworth filter, select and designate the comprehensive range of tidal regimes. The high and low tides, and compute monthly means length of the data series ranged from 1 week to and tidal datums (eg, MLLW, MSL, MHW, etc). four years. The Root Mean Square of the The computations follow the methods outlined in differences between the datums derived using the NOAA Center for Operational Oceanographic the online tool and the NOAA published values Products and Services (CO-OPS) Computational was 4 cm. Techniques for Tidal Datums Handbook. The web Beta Testing service will automatically download data for the control station selected by the user from the CO- The datums output from the tool are only OPS Application Programming Interface. preliminary and should not be used for safety of navigation. The tool does not check the quality Tidal datums for data series that span at least one of the user input data. Errors in the complete month are computed using the Monthly measurements will propagate through to the final Mean Simultaneous Comparison method. Tidal datums. Information on using the tool can be datums for shorter data series are computed using found at www.joasurveys.com. the Tide-by-Tide method of simultaneous comparisons. If a control station ID is not provided, Inputs datums will be computed using the First Reduction  Comma delimited file (mm/dd/yyyy HH:MM, meters) method.  Seven digit control station number, if applicable  Accuracy Email for user Output  Text file emailed to user with final datums and The Online Tidal Datum Computation web service monthly means, if applicable has been tested against 41 water level datasets