APPENDIX 

 SHALLOW WATER ENVIRONMENTAL ANALYSIS 



Introduction 



Here we describe the development of data processing techniques and the subsequent 

 analysis and summarization of sound speed data to support model studies for shallow water 

 locations. A brief qualitative description and analysis of the seasonal sound speed structures 

 are also provided for each of four locations. 



For purposes of this study shallow water is defined in oceanographic terms as the 

 ocean areas overlying the continental shelves. A natural break in the bottom slope near a 

 depth of 200 m often is found marking the edge of the shelf and the beginning of the 

 steeper continental slope. From an acoustic viewpoint, shallow water is water depths 

 where the acoustic waves interact strongly with the ocean surface and bottom and no con- 

 vergence zone paths are observed. The acoustic definition of shallow water therefore can 

 be frequency dependent. This initial study of shallow water acoustics has been restricted 

 to continental shelf regions at depths less than 200 m. 



In our initial attempts to analyze shallow water data, we used the procedures 

 established to select a representative sound speed profile for a particular deep open ocean 

 environment. These did not yield results because of the extreme complexity and variability 

 of profile shapes observed in the shallow water data samples. Because strong emphasis has 

 been placed on the gradient of the vertical sound speed structure for acoustic purposes, 

 analytical procedures were developed to segregate profile types based on the vertical 

 gradient. From these subsets, representative profiles can be selected and model results 

 evaluated on the probability of occurrence of selected profile types. For this study, profiles 

 have been grouped objectively as positive or non-positive gradient profiles with gradient 

 values and percentages of occurrence tabulated. 



Shallow Water Environments 



Four shallow water regions were selected for evaluation during this initial phase of 

 the study. These regions were selected because they each represent a different type of 

 shallow water environment. Specific sites were chosen because a reasonable number of 

 observations were available to support the analysis. (For specific site locations see Figure 

 2.1 in the main text of this report). The Strait of Juan de Fuca off the west coast of 

 Washington at mid latitudes represents a narrow shelf coupled strongly to the open ocean 

 with potential brackish water influence. The shallow North Sea is an example of an 

 isolated adjacent sea and is located at high latitudes. The area East of Singapore was 

 selected to provide a shallow water environment to evaluate the expected weak seasonal 

 effects at very low latitudes. The continental shelf off Lands End in the northeast Atlantic 

 is a wide shelf at high latitudes exposed to open ocean conditions and influenced by the 

 North Atlantic current extension of the Gulf Stream. 



Method of Data Analysis 



The primary source of sound speed data for this analysis was the National Oceano- 

 graphic Data Center (NODC) Nansen cast archival data file. This file provides profiles of 

 ocean temperature, salinity and computed sound speed at standard depths of 0, 10, 20, 30, 

 50, 75, 100, 125, 150 and 200 m. Stations with bottom depths in excess of 200 m were 

 excluded to ehminate observations from the outer continental slope. To supplement the 



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