Patent Application
20080048881
Referring to
Each monitoring station 10 is equipped with a position receiver 60, which monitors transmissions that are generated by transponder(s) 61 of one or more of a group of the electromagnetic receivers 30 that are assigned to the monitoring station 10 for purposes of tracking the positions of the electromagnetic receiver(s) 30 as the electromagnetic receiver(s) 30 descend to the sea floor and for determination of their positions where they rest on the seafloor. For example, the monitoring station 10a may track the positions of the electromagnetic receivers 30a, 30b and 30c; and the monitoring station 10b may track the positions of the electromagnetic receivers 30d and 30e. The position of a particular electromagnetic receiver 30 may be given by, for example, the range, bearing and elevation of the electromagnetic receiver 30; and all of these coordinates may be obtainable via the information that is obtained via the monitoring station's position receiver 60.
In one example, a position receiver 60 is an acoustic receiver that monitors the position of an electromagnetic receiver 30 based on acoustic signals generated by the transponder 61 on the electromagnetic receiver. In another example, the position receiver 60 and the transponder may use radio frequency transmissions. Other examples of a position receiver 60 and a transponder 61 may be used without departing from the scope of the present invention. In addition, it is possible to combine a position receiver and transponder on both the monitoring station and the electromagnetic receivers. In such a case, two-way communication may be achieved between the monitoring station and an electromagnetic receiver.
In accordance with some embodiments of the invention, each monitoring station 10 also includes a transmitter (not shown) to interrogate a corresponding position receiver (not shown) of the electromagnetic receiver 30, which senses the interrogation by the transmitter of the monitoring station 10. Thus, in accordance with some embodiments of the invention, both the monitoring stations 10 and the electromagnetic receivers 30 each includes a transmitter/receiver pair for purposes of tracking the positions of the electromagnetic receivers 30. Each transmitter/receiver pair may be integrated on the same head, in accordance with some embodiments of the invention.
In accordance with some embodiments of the invention, each of the monitoring stations 10 may also include a global navigation satellite (GNSS) subsystem 54 for purposes of acquiring a globally referenced position (i.e., coordinates referenced to WGS-84 datum or an ITRF, International Terrestrial Reference Frame) of the monitoring station 10 using any of the many positioning methods available with GNSS; and each of the monitoring stations 10 may include a wireless telemetry system 70 for purposes of communicating the position of the monitoring station 10 as well as the positions of the electromagnetic receivers 30 that are assigned to the station 10 back to a surface vessel 100. Alternatively, the monitoring station 10 may contain positioning devices other than a GNSS subsystem, in accordance with other embodiments of the invention. Examples of such are terrestrial radio navigation systems (i.e. Loran C, Microfix), passive or active radar reflectors facilitating positioning from the surface vessel or other station using the radar, or optical prisms that can be used with a laser or an electro-optical measuring system in a similar way.
Due to the use of the monitoring stations 10, the electromagnetic receivers 30 may be deployed from the surface vessel 100 and monitored, or tracked, in the following manner. First, from the surface vessel 100, a group of one or more electromagnetic receivers 30 are deployed at the sea surface (via a crane or boom 110 of the surface vessel 100, for example) into the sea, along with an associated floating monitoring station 10 that is configured to track the descent and final location of the electromagnetic receivers 30 of the group. It is noted that each monitoring station 10 may be secured to the seabed via an associated anchor 20. In another example, it may be preferable to use a sea anchor instead of a seabed anchor in deep water. Thus, after being deployed, the electromagnetic receiver(s) 30 descend to the sea bed, while the associated monitoring station 10 floats on the sea surface, while being held in the same general location via the anchor tether.
Each monitoring station 10 acquires its own position from its onboard GNSS subsystem 54. Furthermore, each monitoring station 10 is aware of the relative positions of the tracked electromagnetic receivers 30 due to the position receiver 60 (of the monitoring station 10) and the transponders 61 (of the monitored electromagnetic receivers 30). The monitoring station 10 may wireless communicate (via a wireless telemetry interface 70 of the monitoring station 10) the position of the station 10 and the positions of the monitored electromagnetic receivers 30 to the surface vessel 100 so that the positions of the electromagnetic receivers 30 may be monitored from onboard the surface vessel 100.
More specifically, the surface vessel 100 may include a wireless telemetry interface 104 that receives wireless communications from the telemetry interfaces 70 of the monitoring stations 10. The telemetry interface 104 may, for example, communicate received data, which indicates the receiver positions, to an onboard computer 103 of the surface vessel 100. As an example, the onboard computer 103 may execute software to calculate and display the positions of the electromagnetic receivers 30 so that these positions may be monitored by an operator who is onboard the surface vessel 100.
In accordance with some embodiments of the invention, each position receiver 60-transponder 61 pair is an independent ultra short baseline (USBL) communication system that permits the tracking of the altitude and azimuth and range to the electromagnetic receiver 30. As a more specific example, in accordance with some embodiments of the invention, the USBL communication system is a Global Acoustic Positioning System (GAPS), which is available from iXSea. The GAPS includes an inertial platform that is integrated with the sensor head so that the orientation of it can be accurately monitored without external sensors or measurements. The GAPS is factory-calibrated so that the alignment of the inertial platform axes with the transducer head axes is known. Alternative instrumentations may make use of other acoustic positioning systems co-located with a suitable external inertial platform, but then the alignment of the systems has to be determined explicitly.
As noted above, a single monitoring station 10 may be assigned to one or more of the electromagnetic receivers 30. The number of electromagnetic receivers 30 tracked by a single monitoring station 10 may be a function of the distances between seabed receiver sites and/or the water depth and/or transponder directivity. In accordance with some embodiments of the invention, the receiver-to-monitoring station assignments may be dynamic in nature, so that when a particular receiver 30 is out of range from its originally-assigned monitoring station 10, or better accuracy or update rate may be achieved using another one, another monitoring station 10 may be reassigned to track this receiver 30.
The receiver-to-monitoring station assignments and assignment changes may be directed via communications from the surface vessel computer 103, may be directed via communications among the monitoring stations 10, or may involve a combination of these mechanisms, depending on the particular embodiment of the invention.
For example, in some embodiments of the invention, a human operator onboard the surface vessel 100 may, based on communications from the monitoring stations 10, determine that one of the electromagnetic receivers 30 is too far away from its assigned monitoring station 10. The determination may be based on the monitoring station's inability to acquire the position of the affected receiver or the affected receiver and the monitoring station 10 being separated by a calculated distance (as determined by the computer 103, for example) that exceeds a distance threshold.
The determination of whether a particular receiver 30 is too far away from its assigned monitoring station 10 may also be performed automatically by the computer 103, in accordance with other embodiments of the invention. Once it is determined that the assignment needs to be changed, a human operator or the computer 103 may then signal the appropriate monitoring stations 10 to make the corresponding assignment changes.
Alternatively, the need for assignment changes as well as the assignment changes themselves may be handled automatically via communications among the deployed monitoring stations 10.
As an example of another embodiment of the invention, two or more monitoring stations may each be assigned to track all or a common subset of the electromagnetic receivers 30 in parallel. Thus, many variations are possible and are within the scope of the appended claims.
When the electromagnetic receivers 30 have reached the sea bottom and their final, resting positions have been determined, the surface vessel 100 may then pick up the monitoring stations 10 so that the stations 10 may be reused to assist in the tracking of other electromagnetic receivers 30. In accordance with some embodiments of the invention, a second vessel may be used to assist with picking up the monitoring stations 10. In one example, the second vessel is smaller than the surface vessel 100, and it is configured to deploy and retrieve monitoring stations 10. It is noted that in accordance with some embodiments of the invention, it may be advantageous to have a sufficient number of monitoring stations 10 to cover the entire deployment so that extra rounds with the smaller vessel may be avoided.
Other embodiments are possible and are within the scope of the appended claims. For example, in accordance with some embodiments of the invention, the monitoring stations 10 may be coupled together and towed behind the surface vessel 100 on a tow line 200, as depicted in
As another example of an alternative embodiment of the invention, a near surface vehicle may be used in place of one or more of the buoy-based monitoring stations 10 of
The surface vessel 250 may, for example, tow a streamer that includes an array 300 for purposes of monitoring and positioning the assigned electromagnetic receivers 30. In accordance with some embodiments of the invention, a long baseline (LBL) system may be used in connection with the surface vehicle 250 to monitor the deployed electromagnetic receivers 30.
The LBL system may be also used in conjunction with one of the techniques that are depicted in
Referring to
After the receivers are deployed on the sea bed and used for purposes of performing an electromagnetic survey, the electromagnetic receivers 30 may then be retrieved. More specifically, in accordance with some embodiments of the invention, each receiver 30 may include an acoustically-activated mechanism that causes the receiver 30 to ascend to the sea surface.
In one example, when a particular receiver 30 is to be retrieved from the sea floor, acoustic waves may be communicated from a surface vessel to the receiver 30. In response to this communication, the receiver 30 may activate a surfacing mechanism (a mechanism to cause the receiver 30 to discharge ballast tanks, for example), which causes the receiver 30 to ascend to the sea surface. In another example, the receiver 30 may include a burn wire that is severed using electrical current in the seawater environment upon receiving the surface command.
The ascension of the electromagnetic receivers 30 may be monitored by monitoring stations, similar to the monitoring stations described above. Without this monitoring, the positions of the electromagnetic receivers 30, once surfaced, may be difficult to determine. The ascent of the receiver 30 may take a significantly longer time than its descent, according to some embodiments of the invention.
Referring to
Referring to
It will be appreciated by persons having ordinary skill in the art that while the above description relates to the deployment and positioning of electromagnetic receivers, the invention may be practiced in connection with any subsurface device to be positioned below the surface of the sea, including on the sea floor. For example, a monitoring station may be used to monitor the descent of a seismic sensor or receiver to be located on the seafloor.
While the present invention has been described with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.
