The National Oceanic and Atmospheric Administration (NOAA) is continually striving to decrease the time between the acquisition of multibeam surveys and the updating of charts with information based on those surveys. As part of the process to increase the efficiency and effectiveness of processing hydrographic data, the Coast Survey Development Laboratory was tasked to develop an application that would automate and assist the NOAA oceanographer in developing tidal zoning.

In order to meet this objective, the TIDEZONE software application was developed. The software provides the NOAA oceanographer with a customized Geographical Information System (GIS) project management tool that facilitates the creation, archiving, dissemination and processing of hydrographic survey data with tide zone information. The TIDEZONE application allows the hydrographer to digitally setup tide station zoning for hydrographic surveys. Additionally, the software allows the user to render greater fidelity to the tidal zoning process and automate many steps.

In tidal zoning, a network of closed geographical shapes (usually polygons) are constructed which characterize survey regions of similar range and time intervals referenced to a tide station. Typically each tide zone has an unique range and time correctors referenced to a primary and several backup tide stations. Backup tide stations are incorporated to insure coverage throughout the hydrographic survey, in case the primary tide station malfunctions. The range and time correctors of the tidal zoning are used to compute the tide corrector of a measurement in a zone relative Mean Lower Low Water. The tide corrector along with corrections for ship motion, sensor position and sound velocity are applied to the sounding measurement to obtain a corrected measurement suitable for representation on a NOS chart.

Prior to the use of the TIDEZONE software, tide zone parameters were archived in volumes of notebooks and the coordinates of the zones were originally sketched on paper charts. Once the zones were sketched, each zone's coordinates were manually transcribed to the tidal instruction for a particular hydrographic survey. This was a very cumbersome process, to compile and archive the information. In addition, the oceanographer is typically required to respond to several requests for tidal information simultaneously. This frequent shift of priorities and manual process created a great source of uncertainty about meeting project goals of performance and timeliness. Dealing with this uncertainty was a major concern.

Software Development and Capabilities

This development project took advantage of the relatively inexpensive desktop GIS software available commercially. The proliferation of Geographical Information Systems (GIS) is a technological advance that provides the user with rapid access to geographical and tabular information. The GIS software chosen for the project was MapInfo. This software was chosen because it was relatively inexpensive and user friendly. In addition, we were able to customize MapInfo for the discipline of tidal zoning with a programming language called MapBasic. A variety of databases had to be identified, collected and constructed to give the oceanographer a useful set of information to create tidal zoning schemes. Some of the geographical and informational databases incorporated into the system include:

NOAA Raster Charts

NOS shoreline (1:80,000)

historic tide station data (location, tidal characteristics, bench mark descriptions, elevation etc.)

hydrographic survey boundaries

corange and cotidal lines

hydrographic survey limits and sheet layouts

Chart Historic (CHAPP) data

The software was developed in close consultation with NOAA oceanographers, working in the Ocean Product and Services Division (OPSD). The menu-driven software automated many of the steps that were once manually accomplished, and optimized the basic MapInfo Environment. An example of how geographical information is displayed and the main menu of the TIDEZONE application is shown in Figure 1. Some of the tasks that were automated include the retrieval of shoreline and tide station data with the GIS, report generation of tidezone descriptions, and generation of tidezone ASCII digital files for use with final processing at Marine Centers. The software was designed to assist the oceanographer to develop, maintain and disseminate tidal zoning information. However, it was not intended to replace the oceanographer. The software does not perform automated modeling of coastal water tides estuaries and bays in order to create corange, cophase and tidal zones. Due to the great hydrodynamical complexity of the problem, various methods have been developed with more or less success. Much more work is needed to develop a simple and efficient automated method that can be implemented in a rigorous, practical environment. Thus, the oceanographer is an essential part of the process of interpreting historical and survey observations to develop preliminary tidal zoning before the survey and final tidal zoning after the survey.

When the NOAA oceanographer is assigned a project to develop zoning for a coastal area, it is important that the project be controlled. The oceanographer needs to assess: how much tidal datums have changed, the accuracy of tidal datums, the need to update tidal datums where tide stations are needed to properly characterize a region, the type of mixed tide, the impact of weather conditions, among a great many other things.