Simulation of Internal Wave Wakes and Comparison with Observations
London Research and Development Corp., CANADA
The Loch Linnhe trials were conducted from 1989 to 1994 in Scotland and were designed to evaluate the use of ship-generated internal wave wakes for maritime surveillance by high resolution radar. Examples of these wakes have appeared in the literature. Though the crest structure of the observed wakes is understood, the conditions under which an internal wave wake can be observed by airborne or space-borne radar are still obscure. The purpose of this paper is to describe simulated wakes using a simple model and to compare the results with the observations; this relies on estimating and comparing the surface flow velocities that affect Bragg waves and the resultant radar backscatter. Within the limitations of the internal layer model, the simulations reproduce the crest patterns as expected. The surface flow velocities generated by a number of practical hull forms (e.g. Taylor, Series 60 as well as Wigley) are calculated and compared to those described in the published trial reports. This demonstrates that simple models can explain the characteristics of internal wave wake generation by surface ships moving near the vertical density profile appropriate to a narrow horizontally stratified internal layer. It suggests that the extension of the theory to realistic oceanic diffuse layers will enable the assessment of the practical conditions under which internal wave wakes can be observed. An enhanced simulation should allow the optimization of space-borne radar for the detection of ship internal wave wakes and wake characterization. This could be useful for cross-validating sensor inputs to a Recognized Maritime Picture.