Modeling and Estimation of Tidal Correctors Software Development

As part of the process to increase the efficiency of hydrographic survey verification and processing, the Coast Survey Development Lab was tasked to develop a software package that will assist the NOAA hydrographic survey ships to process multibeam data, in the field, with tidal correctors for survey tracklines across tide zones. Until recently, hydrographic survey track lines were restricted to a single tide zone. This often made assigning survey lines a cumbersome process. The software, called Tide Corrector Generator Version 1.0, is a MapBasic Geographical Information System (GIS) application that compiles and processes water level station, digital tide zones and Computer Aided Resource Information System/Hydrographic Information Processing System (CARIS/HIPS) trackline data files to produce an output file of tidal correctors (relative to MLLW). An example of a trackline processed by software is depicted in Figure 1.

Figure 1- Example of track line processed in the San Francisco Bay

The algorithm to determine the tide corrector closely models that which is performed at the Atlantic and Pacific Marine Centers where they process "smooth" tides. The software also incorporates a decision algorithm that allows the user the flexibility to exclude a particular set of tide stations (referenced by zoning) from being used in processing the tide correctors. The ASCII output file generated is compatible for use with the CARIS/HIPS Multibeam processing system. The output file will be used to apply tidal correctors to hydrographic surveys using the CARIS/HIPS multibeam processing system. A slide demonstration of the Tide Corrector Generator 1.0 software is as follows:

1. Opening Menu

2. Program Setup Menu

3. Load Tide Zone

4. Filter Zoning Table Processing

5. Load DPAS Files

6. Prompt to Graph DPAS File Loaded

7. Graph of Loaded DPAS File

8. Load CARIS Trackline File

9. Tidal Corrector Processing Algorithm

10. Processed Trackline and Zoning

11. COWLIS Output Formatted File

The software was originally developed for use with the CARIS/HIPS Multibeam processor. However, it has a potentially broader usage in increasing NOAA survey vessels capability of performing quick response surveys with any depth sounding processing system such as the Hydrographic Information Data Acquisition and Processing System (HDAPS).

In order to support the requirements of several developmental projects within the Coast Survey Development Lab, more sophisticated algorithms for determining the tidal corrector have been developed. Several projects, that have utilized Global Positioning Systems (GPS) technology to determine ellipsoidal height of the water level surface, have been validated with a more refined model of determining the tidal corrector above Mean Lower Low Water. Algorithms have been developed which incorporate the Delaunay triangulation estimation, natural neighbor interpolation, and moving average estimation.

Revised Thursday October 25 2001by OCS Webmaster