An open-water trial was carried out using a 75 kHz parametric sonar system with the ultimate aim of detecting and characterising submerged objects. This was a contribution to the European Commission's MAST-III DEO (Detection of Embedded Objects) project. The trial involved the detection, in a free field, of scattered signals from a water-filled, thin-walled steel cylinder with flat end-caps. Attempts were made to identify spectral components of the back-scattered signals so that in later experiments, objects that are partially or completely buried may be characterised. Incident and back-scattered signals were recorded using secondary frequencies in the range 1-10 kHz for various target orientations. Comparisons of incident and scattered signals at both primary and secondary frequencies were made for sine wave, chirp and Ricker pulses.
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