Image Number 4 for United States Patent #4319347.
A seismic cable assembly has approximately 500 equally spaced elemental sensor units to receive seismic signals generated in the earth by a seismic impulse generator or "shot". The sensor units each include 3 hydrophones or geophones spaced about 6 feet apart, for a sensor unit length of about 12 feet, to receive seismic signals up to several hundred hertz. Signals representing seismic waves received at each of these 500 units are transmitted from the cable, to a central control and recording unit, mounted in a vehicle such as a towing ship. Connected to the cable will be one or more array-forming systems for processing seismic data from the sensor to synthesize various direction-sensitive hydrophone arrays located along the seismic cable. In combining signals from the individual sensor units making up each array, the array-forming apparatus may increase the relative weighting of signals from selected sensor units in each array and/or may vary the delay between signals arriving at different sensors making up an array. The seismic cable incudes 50 sections spaced apart by electronic connector modules which convert the seismic signals fron analog to digital form, and multiplex the signals for transmission over the cable employing a two-level, channel sequential, time sequential multiplexing technique. The array forming systems may selectively simulate various known arrays without changing the physical configuration of the streamer cable.