Decimeter-resolution 3D seismic volume in shallow water: a case study in small-object detection

Abstract

The 3D Chirp subbottom profiler provides high resolution imaging of coastal and inshore seabed and subseabed structure by combining the known, highly repeatable source waveform of Chirp profilers with the coherent processing and interpretation afforded by true 3D seismic volumes. Comprising sixty hydrophone groups arranged around a Maltese cross of four Chirp transducers, 3D Chirp permits the acquisition of a true 3D volume with a horizontal resolution of 12.5 cm, providing an excellent base for shallow water engineering, archaeological, military, and geological studies. Here we present the results of surveying an atidal basin on the south coast of England aimed at mapping any bedrock protrusions along with the size and distribution of any buried objects. The 150 m by 250 m study area provided a series of unique challenges, including a large number of discrete objects ranging from tens of centimeters to several meters in size, buried in a thin, 0.5 m to 1.5 m, veneer of unconsolidated silt, overlaying a flat bedrock surface showing a high acoustic contrast and short wavelength roughness. Through the comparison of comprehensive post--survey dredging of the entire site with a prestack time migrated 3D volume, it has been possible to confirm a 100 % detection rate for all discrete buried objects larger than 0.30 m by 0.30 m in illuminated area, although one acoustic anomaly could not be accounted for in the dredging results.

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ORCID for Justin K. Dix: orcid.org/0000-0003-2905-5403

ORCID for Timothy J. Henstock: orcid.org/0000-0002-2132-2514

ORCID for Jonathan M. Bull: orcid.org/0000-0003-3373-5807

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