Sub-bottom pipeline and cable detection using automated contact recognition Author: J. KWEE ABSTRACT As more and more wind energy parks are build offshore these days, the need for detecting and mapping the existing infrastructure below the water bottom becomes increasingly vital. Relatively small and easy to deploy sub-bottom profi ling systems provide high resolution 2-D single channel seismics. In this high resolution seismic data, pipelines and cables are identifi ed by the display of hyperbolas. The top of the hyperbola indicates the top of the cable, which is used to determine the exact position and depth of burial. These contacts can be determined manually, taking into account human error and inconsistency. A new development within the geophysical software package Silas is the automated contact recognition technique for the detection of these hyperbolas. The contact recognition consists of the automated determination of two parameters: 1) the semblance of the apex of the hyperbola and 2) the accumulated power of the hyperbola. These parameters are quantifi able fi gures which enables a more objective classifi cation of detected contacts. Other datasets, as multibeam, sidescan sonar and magnetometer data, can be combined with the sub-bottom data within the software for cross correlation and clear imaging of the sea bed and below. INTRODUCTION With the presence of more and more pipelines and cables in the coastal waters, the need to determine the exact location increases. This extended abstract will focus on sub-bottom detections of cables and pipelines using single channel shallow seismic data and describes the automated contact detection of Silas. Vital information with regards to cables is the depth of burial of cables and pipelines. A changing bathymetry can create free span of cables, which could lead to potential dangers of an interrupted power or communication grid. If the location and depth is known, risks can be mitigated before mayor problems arise. Methods using an active signal on pipeline or the cable may detect this properly, but result in a shutdown of the cable for the time of monitoring. A passive method to detect these cables and pipelines is sub bottom profi ling and will be discussed in this extended abstract. Sub-bottom profi ling - Single channel 2-D seismic data Most of the sub-bottom marine infrastructure is situated in the top part of the seabed. Sub-bottom profi ling uses transducers both sending and receiving the signal resulting in 2-D, single channel seismic profi les. These small systems can easily be mounted, also on smaller vessels, allowing easy surveys in coastal and even inland waters. The lower the frequency of a signal, the deeper the penetration, but at the cost of a lower resolution. This tradeoff should always be kept in mind, when picking a frequency for object detection. Important questions are: at what (burial) depth do we expect the cable and what is the size of the object that should be detected. Especially for the detection of cables, a high resolution is needed in the top part of you sub-surface. The beam width and footprint of a sub bottom profi ler are bigger than each of the individual beams of www.stema-systems.nl
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