NEARSHORE SIDE-SCAN SONAR STUDIES

Side-scan sonars operating at 80-250 kHz have been deployed to produce narrow beams directed parallel and normal to shore on a gently slopin g beach. These provide measurements of processes (such as wave propaga tion) seaward of the edge of the surf zone. Shoreward propagation of s ound into the surf zone and hence useful information retrieval from th is zone is prevented, however, by high bubble or suspended sediment ab sorption at its outer edge, as found in earlier Doppler sonar studies at 195 kHz by J. A. Smith. The shoreward limit of acoustic propagation has a variable structure related to incident wave groups, the positio n at which waves break, and to dynamical processes within the surf zon e determining the position of the bubble or suspended sediment boundar y.