imposes a physical limit on both the vertical (depth) accuracy and the 

 spatial resolution possible In utilizing bathymetrlc contouring methods. 



Despite Its Inherent uncertainties, a bathymetrlc contour chart 

 does provide an absolute estimate of depth at all points In space. In 

 the terminology of numerical modelling, a contour chart can be consid- 

 ered a "deterministic model" of sea-floor topography. Because such a 

 model Is analogous to fitting a least-squares surface through randomly 

 spaced, noisy data, It Is by nature a smoothed representation of the 

 actual submarine topography. The degree of smoothing required (or 

 equlvalently the cutoff frequency for low-pass filtering of spatial 

 frequency) depends upon the accuracy, resolution, and density of data 

 used In the contouring. Van Wyckhouse (1973) demonstrated the deter- 

 ministic aspect of bathymetrlc charts with the creation of SYNBAPS 

 (Synthetic Bathymetrlc Profiling System), a data base containing depths 

 on an evenly spaced grid. The grid cell spacing of 5' of latitude and 

 longitude used for SYNBAPS, seems to represent a workable estimate of a 

 suitable interpolation interval for deterministic modelling. Recent 

 work at the U.S. Naval Oceanographic Office has extended this 5' grid 

 world-wide. 



There are also some practical considerations, in addition to the 

 physical limitations, in determining submarine topography to high spa- 

 tial frequencies. Survey instruments such as deep-towed sleds incorpo- 

 rating stereo photography, narrow-beam sounders and side-scan sonar, are 

 able to map small areas of the sea floor with high resolution. However, 

 it is practically impossible to extend these surveys globally, due to 

 the operational difficulties and the great expense of these methods. 

 Another practical difficulty of extending deterministic, gridded models 



