In situ acoustic coring systems for investigating the acoustic and physical properties of mud

Abstract

In situ measurements of compressional and shear wave speed and attenuation provide direct characterization of marine sediment acoustic properties at near ambient conditions, as opposed to measurements that are conducted on samples removed from the seabed. Probe-based acoustic measurement techniques utilize piezoelectric sources and receivers that penetrate the seabed to obtain spatially localized depth-dependent records of compressional and shear waves in the sediment. When such measurements are coupled with conventional coring techniques, sediment samples can be collected from the propagation path between probes, allowing for comparison between the in situ acoustic records and quantities obtained from ex situ core analyses, such as porosity, grain size, or organic matter. Two acoustic coring measurement systems have been developed to investigate the acoustic, physical, and biological properties of soft sediment—the acoustic coring system, a gravity-corer-based platform capable of penetrating the seabed up to several meters, and the acoustic multi-corer, a seabed lander that samples the upper tens of centimeters of sediment near the water-seabed interface. The design and operation of these measurement platforms will be described, along with their capabilities and limitations. Some representative results from field deployments of these systems will be presented. [Work sponsored by ONR.]