Fundamentals of acoustical oceanography

Abstract

The topography and structure of the sea floor are enormously varied. One cannot use one sonar system and one method of data analysis for the whole ocean. The chapter suggests four guiding principles: as the spatial and temporal resolution of sonar systems improve, more and more small features are displayed; as the frequency of a sonar goes lower, the sea floor appears to become smoother; there are always unresolved features; and global positioning systems and accurate navigation are absolutely essential. Vertical echo sounders are the workhorses of marine geology and geophysics. Bottom-scanning sonar technology has gone from a simple echo sounder pointed sideways to instruments that have carefully designed beam patterns, very sophisticated time-varying gains, and image processing. The bottom of sea has smooth sediments, gravel, wave-like features, and just plain puzzling features. Smooth-sediment-covered areas have very small uniform surface-scattering coefficients. Ridges, gravel beds, sand waves, grooves, and so forth show as dark and light features. It takes much geological imagination to guess what the images represent.