COMBINING SIGNALS FROM CONDUCTOR PAIRS IN A GEOPHYSICAL SURVEY CABLE IN ORDER TO REDUCE NOISE

A geophysical survey cable (16, figure 1) includes a signal amplifier 20 coupled between two electrodes 18 spaced apart along the length of the cable. The electrodes being coupled to the signal amplifier by a first conductor pair 17. A noise amplifier 30 is coupled to a second conductor pair 27 positioned substantially parallel to the first conductor pair. Electrical noise eg from underwater pipelines, cables or from the movement of the towed cable is superimposed on the sensor signal through conductor pair 17. As a result, the sensor signal that appears on an output node of signal amplifier 20 has both an input signal component and an input noise component. Because the second conductor pair 27 is configured similarly, but without being coupled to the electrodes, the output of noise amplifier 30 has only the noise component. This noise component can be measured from the output of noise amplifier 30 and subtracted from the output of signal amplifier 20 to provide a sensor signal with a reduced noise component. The geophysical survey cable may further include a combiner that combines the noise signal provided by the noise amplifier with the sensor signal provided by the signal amplifier.