ASSESSMENT OF THE IMPACT OF UNCERTAINTY IN SEABED GEOACOUSTIC PARAMETERS ON PREDICTED SONAR PERFORMANCE

摘要

'Uncertainty' can be distinguished from Variability' as the lack of knowledge of the input variables that a certain calculation must tolerate. In the case studied here, the calculation concerns sonar performance, and uncertainty may stem from many sources including the finite measurement precision of methods used to describe the physical environment. Lack of knowledge of the environmental inputs causes uncertainty in the predicted sonar performance. It is common for this uncertainty to be high but its impact is rarely taken into account. In this paper we take, as an example of an environmental descriptor, plane wave reflection loss already derived from measurements of ambient noise directionality. An inverse method is developed that allows the reflection loss as a function of angle and frequency to be converted to a geophysical description of the seabed in terms of density, sound speed and attenuation. The uncertainty in these geophysical 'inputs', i.e. the "error bar" associated with the inversion, is estimated and the impact of this uncertainty on the prediction of sonar performance is calculated. This is achieved by calculating reverberation and target echo in a series of environments lying within the uncertainty bounds. These calculations are repeated using seabed data derived from a geophysical description of a core. The relative impacts of the uncertainties associated with the two methods of describing the seabed are compared. The calculations performed also take into account uncertainty in sonar-related parameters such as target reflectivity.