Method for maintaining a constant tension on a seismic marine cable
AssigneeWestern Geophysical Company of America
InventorCarl H. Savit
Life of this patent
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Abstract
A method for maintaining a substantially constant tension on a towed seismic cable, wherein the instantaneous towing force and the instantaneous cable displacement relative to a fixed shipboard reference are continously measured and sampled. A microprocessor associated with a servo controlled capstan device, uses those measurements to pay out cable or to retrieve cable in response to an increase or decrease in the instantaneous towing force. The microprocessor also tries to minimize the average cable displacement.
Claims5
A method for maintaining a substantially constant force on, and an average displacement relative to a shipboard reference of, a ship-towed seismic cable having a tow line secured to the head end thereof, comprising the steps of:
- sampling and measuring at desired sample intervals, the instantaneous towing force exerted by said towed cable;
- establishing a force window having upper and lower force limits;
- paying out a portion of said tow line when the measured towing force exceeds said upper force limit and retrieving a portion of said tow line when the measured towing force falls below said lower force limit;
- measuring the average displacement of said tow line relative to a fixed shipboard reference;
- minimizing the average displacement of said tow line;
- maintaining a running average of the instantaneous towing-force measurements over a desired time interval;
- determining a desired statistic from said towing-force measurements;
- and
- applying said statistic to said running average to define the upper and lower limits of said force window.
Dependencies are inferred from the claim text.