System and method for controlling the position of a instrument cable towed in water

Method for controlling an instrumented cable towed in water, such as a marine seismic streamer, and/or an instrumented towed cable array (streamer array), to which instrumented cable(s) control devices are arranged for controlling the individual instrumented cables both in shape and position in relation to other instrumented cables and by that counteract crosscurrents and/or other dynamic forces affecting a towed cable array behind a seismic survey vessel, and to which instrumented cable(s) tail buoys and deflector device(s) are arranged, a control/command central being arranged on said vessel for controlling the instrumented cable or cable array, which control/command central is arranged to communicate with the one or more instrumented cable(s) and the vessel includes an operator unit,

• characterized in that the method includes the following steps:
• a) acquiring status and information about instrumented cable(s) and control device(s);
• b) acquiring navigational information for tail buoy(s), vessel and optionally deflector device(s), which tail buoy(s) and deflector device(s) are provided with acoustic transmitter/receiver means and electronics for acoustic ranging;
• c) configuring the control device(s), which control devices includes at least two wings provided with acoustic transmitter/receiver elements and electronics for direction-controlled measurement of distances between adjacent control devices on parallel towed cables, to transmit and receive acoustic signals/pulses for acoustic ranging, including
• c1) configuring each control device of the instrumented cable(s) to transmit by means of the at least two transmitter/receiver elements simultaneously on one of y channels and configuring each control device of the instrumented cable(s) to receive by means of the transmitter/receiver elements on all y channels,
• c2) chose an instrumented cable and configure the control device(s) on the selected instrumented cable to transmit by means of the at least two transmitter/receiver elements simultaneously on channel 1, channel 2 . . . , channel y, channel 1 . . . successively along the selected instrumented cable,
• c3) command all control devices on the selected instrumented cable to transmit pulses/signals by means of the at least two transmitter/receiver elements at time T0+X1s through a broadcast message simultaneously to all control devices to provide multiple measurement per range per interrogation,
• c4) command all control devices on all other instrumented cables in a cable array to receive by means of the transmitter/receiver elements signals/pulses with ID after time T0+X2s,
• c5) report ID and ranges for signals/pulses with ID received after time T0+X2s, where X2>X1, to the control/command central on demand, where control devices on different instrumented cables preferably transmit by means of the at least two transmitter/receiver elements simultaneously to limit the time it takes to report all measured distances in the cable array,
• c6) after all control devices on the selected instrumented cable have finished transmitting, the control devices of a next selected instrumented cable are commanded for transmission, while the control devices on the first selected instrumented cable which has been transmitting is commanded to receive,
• c7) repeat steps c1)-c6) for all instrumented cables in a cable array for complete acoustic ranging of the instrumented cables in the cable array;
• d) calculating relative and absolute positions, sound velocities between known positions and position Cross-Track-Error and Cross-Track-velocity based on step c);
• e) calculating and defining settings for control device(s) based on information from steps a)-d);
• f) providing the control devices with settings, state modes, control commands for providing an accurate, robust and less energy demanding control of the cable array;
• g) repeat steps a)-f) continuously.