The Application of Distributed Acoustic Sensing for Shallow Marine Investigations an Intertidal Case Study

Abstract

Summary Typically, there is a paucity of geotechnical information available to designers of offshore foundations for marine renewable structures, which often results in highly conservative designs. With an increased recognition of the value of shear wave velocity measurements as a critical design parameter in the marine geotechnical industry, there is a real requirement to develop a cost effective shear wave seismic data acquisition methodology. This case study documents field trials at Dollymount Strand, Dublin using fibre optic cables as continuous seismic sensors for the collection of surface wave data. Data were collected using an OptaSense ODH4 interrogator connected to a 1000m long CST armoured single mode fibre optic cable. A Sercel Mini G airgun, operated from a survey vessel, was used as the seismic source. The collection of data from an intertidal site allowed for direct comparison of different acquisition methodologies in both dry and flooded conditions. The findings of the study showed that Distributed Acoustic Sensing (DAS) was effective at collecting shallow marine seismic data for analysis using the Multichannel Analysis of Surface Waves (MASW) method. Using DAS in this environment has great potential due to the rapid data acquisition compared to other currently available technologies.