Methods and apparatus for indicating an underwater parameter in a marine seismic system

Claim 1

IN A MARINE SEISMIC SURVEY SYSTEM, A DEVICE FOR INDICATING AN UNDERWATER PARAMETER AT LEAST ONE POINT ALONG THE LENGTH OF THE CABLE, COMPRISING: (A) AT LEAST ONE PARAMETER MEASURING DEVICE LOCATED AT AT LEAST ONE POINT ALONG THE LENGTH OF THE CABLE; (B) FIRST MEANS FOR SUPPLYING A PULSATING, POLARITYREVERSING DIRECT CURRENT SIGNAL TO THE PARAMETER MEASURING DEVICE, SAID FIRST MEANS INCLUDING: (1) MEANS FOR SUPPLYING A DIRECT CURRENT SIGNAL; (2) PULSATING MEANS FOR PERIODICALLY REVERSING THE POLARITY OF THE SIGNAL FROM THE DIRECT CURRENT SUPPLYING MEANS TO THE PARAMETER MEASURING DEVICE; AND (C) SECOND MEANS RESPONSIVE TO THE PARAMETER MEASURED BY THE PARAMETER MEASURING DEVICE FOR PROVIDING AN INDICATION OF THE UNDERWATER PARAMETER, THE CHANGES IN THE PARAMETER CAUSING THE PARAMETER MEASURING DEVICE TO VARY THE MAGNITUDE OF THE PULSATING, POLARITY-REVERSING DIRECT CURRENT SIGNAL APPLIED TO THE SECOND MEANS.