oa 3D-3C Distributed Acoustic Sensing Arrays in Marine Geophysics

Distributed Acoustic Sensing (DAS) is a valuable geophysical technique for real-time seismic signal monitoring using an entire fiber-optic cable. However, it has limitations, including single-component measurements, fiber directionality, and low signal-to-noise ratios (SNR). We introduce the concept of “DAS radar” with a 3D-3C DAS array to address these issues. The 3D-3C DAS array consists of 4388 fiber sensors arranged in a cross and concentric circle (CCC) pattern on the seafloor, with the additional fiber cable deployed vertically in seawater. By calculating travel times and differential travel times (DTT) from a seismic source, the array can determine source azimuth and incidence angles. This information helps correct DAS amplitude distortion due to fiber directivity and enables us to construct hodograms for 3C DAS array data analysis. Thousands of fiber sensors provide an opportunity to enhance SNR using beamforming and coherent stacking methods. The 3D-3C DAS array has numerous marine geophysics applications. It can be used for 3D-3C migration imaging of subsurface structures, monitoring seawater velocity and temperature, tracking CO2 injection and migration, and detecting submarine volcanic and seismic activities. It can also image shallow formations, monitor geo-hazards, track marine mammals, and traffic monitor and control in shallow waters. We conclude that the 3D-3C DAS array is a promising tool for marine geophysics that overcomes some limitations of current DAS measurements, offering versatile applications in marine geophysics for subsurface imaging, environmental monitoring, geo-hazard detection, and marine life tracking.