In underwater acoustic navigation of a marine seismic spread, ranges are measured to determine the geometric relationship between the seismic equipment and a position of the seismic equipment and the spread. An accurate range is the travel time of the direct arrival of a signal from a pinger by a particular receiver. The direct arrival is the acoustic signal traveling along the path of shortest travel time in the water column without being influenced by the reflection from a boundary. Reflections from a boundary, the sea-surface or sea floor, travel a longer distance than the direct arrival signals and are therefore subject to a time delay relative to the direct arrival. Tracking the reflections rather than the direct arrival signals may deteriorate the acoustic ranges and may cause the acoustic network solution to deteriorate, resulting in a deteriorated positioning of the seismic equipment.
Historically, the ranges with time delays due to reflections are filtered to avoid their introduction in the positioning solution. The traditional methods for “editing” the ranges have been manual, i.e. by adjusting the range by subtracting the effect of the reflection or by setting a range to passive. These prior art methods for editing are manageable for positioning systems that rely on only a few hundred ranges. However, these prior art methods fail when the number of ranges increase. For example, WesternGeco's intrinsic range modulated acoustic ranging system may include more than 10,000 ranges.
Therefore, it is a desire to provide a method of selecting the direct range for accurately positioning marine seismic equipment that addresses drawbacks of the prior art methods. It is a further desire to provide a method of range selection that utilizes information about the seismic spread as well as environmental parameters to predict direct arrival and reflected arrival of a signal by a receiver. It is a still further desire to provide a method for rejecting reflected signals that are received. It is a still further desire to condition a range based on a received reflected signal.
USPTO Backgrounds
USPTO Backgrounds