THE INFLUENCE OF OPTICAL-PROPERTIES OF SHALLOW SHELF SEAS ON TEMPERATURE STRUCTURE AND ACOUSTIC PROPAGATION

The penetration of solar radiation below the sea surface is not always taken into account in numerical ocean models, even though its influen ce on the temperature (and therefore sound speed), structure of the wa ter column can be significant, especially in shallow shelf seas where water turbidity tends to be high. Variations in sound speed structure have a consequent effect on the propagation of sound underwater which, in turn, influences the performance of sonar systems. A double expone ntial parameterization for the penetration of solar radiation with dep th was implemented in an N x1 D turbulence closure model of the UK she lf seas. The model was run along a section through the Celtic Sea Fron t, with sets of optical extinction coefficients representing different water clarities, for one month to simulate the generation of the fron t, and the results were compared with a control model run in which all solar radiation was absorbed in the surface layer. Temperature struct ure and sound propagation were only affected by changes to the optical parameterization on the stratified side of the front, where consequen t variations in acoustic propagation loss of up to 10 dB relative to t he control were simulated using an acoustic model. Changes in propagat ion loss were greatest for acoustic sources placed in the stratified w ater above the thermocline. Similar changes to the optical parameteriz ation made on the well-mixed side of the front had no discernible effe ct. Crown copyright (C) 1996 published by Elsevier Science Ltd.