Seismic cable for use with array terminal type acquisition systems

Claim 1

In a seismic data gathering system in which a plurality of S geophones are connected by analog conductor pairs into each of a plurality of T array terminals (AT), providing a total of TS geophones, the ATs are spaced along a line a distance D apart, and the S geophones for each of the T ATs are spaced uniformly along the line of ATs at distances D/S apart, and in the ATs the S pairs of analog conductors carry S geophone signals which are amplified, digitized, the digital bits are stored, and on command, are read out of storage as a train of digital bits over a digital conductor pair to and through the next downline AT and to a recording unit; the improvement in cable system comprising; (a) a first AT, and a second spaced-apart AT next downline toward a recording unit, and a third spaced-apart AT next upline toward the end of the line farthest from said recording unit, each of said ATs having two identical ports and identical receptacles in each port; (b) a first cable connected to a first port in said first AT and connected to a first port in said second AT; and a second identical cable connected to the second port in said first AT and connected to a first port in said third AT; (c) said first cable containing at least one digital conductor pair and S/2 analog conductor pairs connected to said first port in said first AT and connected respectively to S/2 geophones positioned D/S apart downline toward said second AT, and spaced substantially a total distance D/2 downline from said first AT; (d) said second cable, containing at least one digital conductor pair and S/2 analog conductor pairs connected to said second port in said first AT, and connected respectively to S/2 geophones positioned upline D/S apart toward said third AT, and spaced substantially a total distance of D/2 upline from said first AT; whereby the minimum number of analog conductor pairs entering eacb port is S/2 , one group of S/2 conductor pairs extending D/2 downline, and a second group of S/2 conductor pairs extending D/2 upline from said first AT; (e) said first and second cables are identical and can be turned end for end, and each comprises a bundle of at least one digital conductor pair, plus S/2 analog conductor pairs, said S/2 analog conductor pairs being cut at the midpoints of said cables while said at least one digital conductor pair is continuous from one end of said cable to the other; whereby the S spaced geophones positioned between each pair of ATs, are connected half into each of the two adjacent ATs, and said at least one digital conductor pair is connected continuously between adjacent ATs.