Monitoring the Coastal Environment; Part III: Geophysical and Research Methods

Andrew Morang, Robert Larson, Laurel Gorman

Abstract


Acoustic and electromagnetic geophysical methods are widely used in coastal studies for determining water depth, identifying bottom sediment type and surficial features, locating man-made objects and hazards, and studying sub-bottom geology and structure. Acoustic methods are broadly divided into categories: 1. high-frequency systems such as echo-sounders whose main purpose is to determine water depth (minimal seafloor penetration); 2. lower-frequency systems with the ability to penetrate bottom sediments. Coastal hydrographic surveys must be conducted by qualified personnel with meticulous quality-control procedures. The maximum practicable achievable accuracy for coastal surveys using echo sounders is about ± 0.5 ft (0.15 m). High-resolution seismic surveys are used for engineering and for beach fill studies. The thinnest bed or layer that can be detected is about λ/4, where λ is the wavelength of the acoustic source.


Keywords


Depth sounding; sub-bottom profiling; side-scan sonar; ground penetrating radar; hydrographic surveying; acoustic impedences; high -resolution seismic

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