HOW TO PLACE SOUND SOURCE AND STREAMER RELATIVE TO EACH OTHER ?

Should the electrode be placed in the middle of the streamer ?

What is the proper distance Electrode-Streamer ?

The normal set up of the shallow water seismic acquisition is with the signal emission (sparker or boomer) on one side and the signal reception (streamer) on the other side.

It is important to avoid the ship propeller's noise.

 

A streamer almost always includes several hydrophones, in an attempt to improve the signal-to-noise ratio (S/N).

The length of the active section, between the first and the last hydrophone (for one channel), should not exceed the wavelength of the acoustic source.

ex for a sparker centered  around 1000 Hz, the wavelength is of 1.5m.

 

This is to avoid a destructive interference due to the phase difference between the first and the last hydrophone.

The source emission should be placed at the middle of the active section.

 

The ghosts from the source or the streamer also affect the received signals, with notches in the frequency domain.

The notch in frequency = 2 z/v, with z the depth of the source or the receiver, and v the speed of sound in water.

ex for a source at 0.3 m, the notch is at 2500 Hz

ex for the streamer at 0.1 m the notch is at 7500 Hz.

This is why the streamer must be towed at an ideal depth, to minimize that destructive interference (notch) between reflected signals and multiples from the air/water interface, which is called the receiver ghost.

Normally the streamer are balanced correctly so that the section is horizontal in the water. 


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