TIME-DOMAIN AND FREQUENCY-DOMAIN ANALYSIS OF ACOUSTIC SCATTERING BY SPHERES

In recent years the application of resonance scattering theory, RST, to the interaction of underwater sound with elastic bodies, has yielded a description of the scattering process that has provided valuable insight into the underlying mechanisms of scattering. Comparisons of this approach with observations have usually been carried out in the frequency domain, using the form function notation. In the present study results are reported of an examination of the backscattered echo from a selection of spheres conducted both in the time domain and the frequency domain. The structure of the background and resonance components of the backscattered signal are investigated, and examined in both domains. To obtain the measurements a linear frequency-modulated signal or chirp was employed. Using a Fourier analysis approach, with pulse compression, measurements have been taken in the time domain, which readily show the components of the backscattered echo. Using these data, sections of the record have been separately transformed to obtain in the frequency domain the background and resonance form functions. Further, time-frequency plots have been generated to examine the association between the time domain echo and the form function structure. To compare the observations with predictions, resonance scattering theory has been applied both in the time domain and the frequency domain.