Apparatus and method for locating towed seismic apparatus

#This invention relates to marine seismic exploration, and more particularly, relates to determining the positions of towed marine seismic sources, towed marine seismic detectors, and other towed marine apparatus.

#In marine seismic exploration, various impulsive sources, which are typically air guns, may be suspended at some preselected depth beneath a float, or some other type of support apparatus. The float or apparatus is in turn towed by an exploration vessel; there may be a plurality of such floats or apparatus towed behind the exploration vessel. The exploration vessel may also tow a streamer cable, or another exploration vessel may tow the streamer cable. The streamer cable contains detectors to detect energy propagating upwardly from subsurface strata lying beneath the body of water in which the vessel operates.

#The exploration vessel may determine its precise location in the body of water through the use of conventional navigation systems. Although such systems may be employed to determine the vessel's location, they generally do not determine the location of any source floats or apparatus, or streamer cable. Other onboard equipment must be employed to determine the location of the floats or apparatus, or streamer cable that may be in many different positions and at various distances depending upon the source and/or detector arrays employed.

#FIG. 1 is a plan view of a vessel towing marine seismic apparatus.

#FIG. 2 is a simplified block diagram of one embodiment of the apparatus depicted in FIG. 1.

#FIG. 3 is a simplified plan view of a portion of the apparatus depicted in FIG. 1.

#Referring now to FIG. 1, there may be seen a plan view of a vessel 5 towing a plurality of floats 21-28 and a streamer cable 29. Although floats 21-28 are depicted in FIG. 1, any other type of towable supporting apparatus capable of supporting the seismic sources at some predetermined depth are considered within the scope of the present invention; the term "float" or "floats" is used herein to mean any such type of towable supporting apparatus. More particularly, the exploration vessel 5 has mounted thereon an acoustic phased array assembly 10 (see FIG. 2), which may be extended below the hull of vessel 5 by conventional apparatus that is commercially available.

#Vessel 5 also has appropriate towing gear 18 and 19 for towing floats 21-28 with cables 20. Further, vessel 5 is towing a marine seismic streamer cable 29 by means of appropriate towing gear (not shown). Although eight floats and one streamer cable are depicted in FIG. 1, these numbers are by way of illustration only and are not intended as any limitation on the scope of the invention.

#Floats 21-28 may have suitable marine seismic sources disposed beneath them. Floats 21-28 may also have acoustic sources 31-38, respectively, located thereon, or adjacent the float and near the seismic source, in accordance with the concepts of the present invention. These acoustic sources 31-38 are preferably activated by signals sent over electrical wires from the vessel 5. This allows for simple and reliable apparatus to be located on or near the float where it is subjected to mechanical shocks each time the seismic sources are fired. These electrical wires are preferably in a wiring type harness that is attached to towing cable 20, although they may also be included in the towing cable 20.