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Shallow Seismic

For a majority of this work we use a EGG Uniboom sub-bottom profiling system.

For high resolution surveys not requiring deep penetration we use an ORE Pinger and for projects requiring deep penetration where high resolution is not as essential, we use a Sparker.

The boomer system consists of an insulated metal plate and rubber diaphragm adjacent to a flat wound electrical coil mounted on a towed catamaran.

A short duration, high power electrical pulse, generated by the shipboard power supply and capacitor banks, discharges to the electrical coil. The resultant magnetic field explosively repels the metal plate generating a broad band acoustic pressure pulse in the water column.

The frequency of this pulse is in the range 400Hz to 14Hz with the majority of the energy being directed vertically downward at a maximum output of 300 joules per pulse.

A percentage of the acoustic energy is reflected from the sea floor. This percentage is dependent upon the composition of the seabed materials. The remaining energy penetrates the seabed and is reflected from layers of contrasting acoustic impedance. Acoustic impedance is a product of the density and seismic velocity of the material.

The reflections are detected by a multi-element hydrophone which is towed parallel to the source catamaran, astern of the vessel. This configuration is used in order to minimise the direct source-receiver signal.

The reflections detected by the hydrophone are converted to an electrical signal which is amplified, filtered and displayed in graphic form on the seismic recorder.

The character of the sub-bottom records are therefore dependant upon the way in which the acoustic signal is reflected. This is used to interpret the condition present. An Ultra 120 series, 3 channel thermal recorder will be used to display the data graphically on board with the incoming data being enhanced by the use of an in-line TSS 360 Shallow Seismic Processor.

Processed seismic data will be produced on an Isopach and for pipe route investigations we would also provide a longitudinal section.

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