PRODUCTS FROM TWO COMPUTER PROGRAMS WHICH 

 PROCESS DIGITAL BATHYMETRIC DATA 



by 

 Barry E. Herohenroder 



I. INTRODUCTION 



Regularly spaced bathymetric data are needed by the U.S. Army, Corps of 

 Engineers for input to various numerical models which describe coastal phenom- 

 ena such as storm surge and wave refraction. Bathymetric contours produced 

 from such data are also sometimes needed to help locate important bathymetric 

 features or changes in a project area. To generate regularly spaced bathy- 

 metric data, an adequate set of raw irregularly spaced data must be available 

 and a method to interpolate-extrapolate this data to regularly spaced locations 

 is required. This report describes a large set of bathymetric data available 

 on magnetic tape and products from a computer program which generates regularly 

 spaced data from the raw data; products from a program which generates contours 

 from the regularly spaced data are also described. 



One source of raw bathymetric data in an area affected by a coastal project 

 may be survey data taken as part of the project. If there are no such data or 

 if the project survey data must be supplemented, a major additional data source 

 is the National Ocean Survey (NOS) digital hydrographic data set available from 

 the National Geophysical and Solar-Terrestrial Data Center (NGSDC) of the 

 National Oceanic and Atmospheric Administration (NOAA) . Data from both data 

 sources normally have an irregular spacing. 



Interpolating-extrapolating irregularly spaced data to regularly spaced 

 locations is onerous when done by hand. Drawing depth or bed elevation con- 

 tours by hand is also time consuming and tedious. To simplify these tasks at 

 the Coastal Engineering Research Center (CERC) , two computer programs, ZGRID1 

 (program No. 720X6RICG0) and CONTOR (program No. 720X6R19X0) , have been devel- 

 oped or modified. ZGRID1 interpolates or extrapolates and CONTOR determines 

 and draws contours. The two programs are available with documentation from the 

 Engineering Computer Programs Library at U.S. Army Engineer Waterways Experiment 

 Station, Vicksburg, Mississippi. Both ZGRID1 and CONTOR require large, fast 

 computers, e.g., CDC 6600, CDC CYBER176, CRAY-1, IBM 3033, and use standard 

 CALCOMP plotting commands. 



II. NOS DIGITAL DATA 



A few years ago, NOS began digitizing U.S. coastal hydrographic data from 

 about 3,200 survey sheets. Most of the resulting digital data have been 

 archived with the NGSDC; they are available on magnetic tape for a fee by writ- 

 ing or phoning National Geophysical and Solar-Terrestrial Data Center, Code 

 D621, EDS/NOAA, Boulder, Colorado 80302, phone (303) 499-1000, extension 6338 

 (FTS 373-6338). A detailed description of the available digital data, as well 

 as pricing information, is given in National Geophysical and Solar-Terrestrial 

 Data Center (1976, 1979a, 1979b, 1980) and in Lawrence (1977). The digital 

 data are irregularly spaced in latitude and longitude and consist of about 97 

 percent depth soundings and 3 percent bottom characteristics (e.g., clay, mud, 

 soft, etc.) and dangers to navigation (e.g., wrecks, pilings, etc.) The 1 

 square areas along the continental United States and Alaskan coasts for which 



