Bottom Transponders Research Articles

Precise Positioning of a Sea Bottom Transponder (4)

In the previous papers, it is shown that not only the position of a bottom transponder but also the underwater acoustic velocity distribution can be determined, if the position of surface transponders and ranges between the surface and bottom transponders are known. Also, a theoretical possibility was shown that the position of the bottom transponder can be obtained in the order of centimeters by using equipments available now. They were extended to three-dimensions in the third paper. More realistic results were obtained there. In the present paper, the theory is extended to include the effects of current. The basic nonlinear equations are obtained by a variational principle. Some two-dimensional numerical calculations are conducted, and the convergence of the iteration calculations is verified. The numerical results show that the effects of current can be obtained and can't be neglected for precise positioning.

Three Dimensional Calculation

According to the first report, not only the position of a sea bottom transponder but also the underwater acoustic velocity can be determined, if the position of sea surface transponders and the distances between the surface and bottom transponders are known. In the second report, a theoretical possibility of obtaining the position of the sea bottom transponder with accuracy of centimeter order is shown. For the purpose, estimation of the underwater acoustic velocity distribution as a part of solution is extremely important. Effects of errors in the positions of the surface transponders and the distances between the surface and bottom transponders are also obtained in detail. In the previous papers, two dimensional calculations are conducted.In the present paper, more realistic simulations are conducted by introducing three dimensional calculations. And a new idea called MIL (Method of Incremental Layers) are developed to stabilize numerical calculations.

Precise Positioning of a Sea Bottom Transponder (1)

A method to determine precisely the position of a transponder placed at a sea floor under a condition that the underwater environment (the sound velocity distribution) is not known is discussed. Not only the position of the transponder but also the unknown underwater parameters can be determined at the same time, if the acoustic rays whose number is equal to or more than that of the unknowns are obtained. The effectiveness of the method is verified by numerical simulations. If only the precise determination of the position of a sea bottom transponder is required, two or three horizontal layers may be sufficient, when a calculation method where underwater sound field is divided into horizontal layers is used.

Acoustic navigation for a large aperture array

The acoustic navigation system for a large aperture (900 m) vertical array and the resulting data, describing the motion of the array and research platform FLIP during a 20‐day deployment in the NE Pacific, are presented. Acoustic navigation data are acquired by detecting the high‐frequency signals emitted by near bottom transponders. Recorded travel times are converted to xyz positions by a nonlinear least‐squares approach that adjusts the transponder, FLIP, and the array positions, minimizing the rms error. Simulation results highlight error sensitivities. The movement of FLIP, although constrained by a three‐point moor, exhibits a wind‐driven component and a clockwise semidiurnal tidal component with horizontal displacements in excess of 300 m. Suspended vertically from FLIP under tension, the array has a damped response to tidal and internal wave forces. [Work supported by ONT.]

Underwater positioning by long‐baseline acoustic navigation system and relocation of transponders

Abstract A newly developed, compact long‐baseline (LBL) acoustic transponder system, used in several experiments for submarine and sea surface positioning, has proven to be easy to operate and reliable. Relocation of the ocean bottom transponders can be carried out to minimize vertical component errors of ship's positions. A transponder net is usually located via Loran‐C navigation in the western Pacific. Accuracy of positions acquired after relocation of the transponders is estimated to be a few meters at a slant range of several thousands of meters. Because several experiments have shown the difficulty of pinpointing the movement of an instrument towed from a ship, a transponder system is indispensable to precise underwater experiments.

Submerged marine streamer locator

Method and means are provided for determining the position of a submerged marine streamer towed behind an exploration vessel. An array of at least three transponders secured to the ocean floor generate distinguishable acoustic pulses upon a command signal from the ship. These signals are received by hydrophones housed in the streamer and by the ship. The distance to each hydrophone may be triangulated from the data generated including accounting for changes in velocity between the vessel and the seismic streamer and the bottom transponders during the taking of such data.

Ocean bottom control using the global positioning system

Abstract One of the most fundamental challenges of working in the ocean environment is the establishment of a geodetic control system, similar to the more familiar geodetic networks on the earth's land areas. Applications of ocean bottom control network, which are well‐identified by the marine community, are numerous. The NAVSTAR constellation of the Global Positioning System (GPS) provides a unique capability. The expected visibility of its four to seven satellites anywhere anytime on the earth's surface will enable instantaneous real‐time positioning of a buoy, thus eliminating complex mathematical modeling of its motion. This buoy can simultaneously be triggered to measure ranges to a network of ocean bottom transponders through acoustic link, thus replacing the conventional expensive use of a ship. The concept takes advantage of a double pyramid formed between GPS satellites and the transponders linked via buoy. The measured ranges, solved in the geometric mode through the least squares method, will t...

Observations on Cretaceous abyssal hills in the northeast Pacific

An abyssal hills area of 50 × 60 km in the northeast Pacific was studied using bottom transponder navigation, closely spaced survey lines, and long-traverse oblique photography. The block-faulted north—south hills are bounded by scarps, commonly with 40° slopes. On these steep scarps sedimentation is inhibited and pillow basalts often crop out. An ash layer of high acoustic reflectivity at about 7 m subbottom depth blankets the area. This ash occurs in multiple beds altered to phillipsite and is highly consolidated. A 24 m.y. age for the ash is based on ichthyolith dates from samples in the overlying sediments. Acoustically transparent Neogene sediments above the ash are thickest in trough bottoms and are absent or thin on steep slopes. These Neogene sediments are composed of pale-brown pelagic clays of illite, quartz, smectite, chlorite and kaolinite. Dark-brown pelagic clays, rich in smectite and amorphous iron oxides, underlie the Neogene surficial sediments. Manganese nodules cover the bottom in varying percentages. The nodules are most abundant near basement outcrops and where the subbottom ash layer is absent.

Use of GPS in ocean‐bottom control

Abstract : The NAVSTAR constellation of the Global Positioning System (GPS) provides a unique capability. The expected visibility of its four to seven satellites anywhere anytime on the earth's surface will enable instantaneous in real time positioning of a buoy, thus eliminating complex mathematical modeling of its motion. This buoy can simultaneously be triggered to measure ranges to a network of ocean bottom transponders through acoustic link, thus replacing the conventional expensive use of a ship. The concept takes advantage of a double pyramid, which is formed between GPS satellites and the transponders linked via buoy. The measured ranges, solved in the geometric mode through the least squares method, will thus provide geodetic positions of transponders. The present paper discusses the concept details and develops the mathematical model for the system. Some simulated results of this novel approach are also included.

Acoustic under sea position measurement system

The invention concerns acoustic under-water measurement apparatus for determining the location with respect to a surface vessel of objects such as submersible vessels, pipe-riders, mining apparatus, or the like, including tethered submersible vessels. A receiver hydrophone set located on the tethered vehicle receives acoustic reply pulses from sea bottom transponders, telemetering the times of reception to a surface support ship via conductors in the tether cable. Signals obtained at the surface ship directly from the transponders and indirectly via the tether cable conductors are combined aboard the surface ship for computing the positions of both vessels with respect to a base line established by the sea bottom transponders. The system is self-calibrating, so that an expensive survey to determine the actual locations of the bottom transponders is no longer required.

Precise positioning for near-bottom equipment using a relay transponder

The Marine Physical Laboratory of the Scripps Institution of Oceanography has developed an acoustic relay transponder for precise relative positioning of near-bottom instruments and geologic sampling devices. Although specifically designed to position equipment lowered on standard wire ropes without a need to maintain direct electrical contact with the surface ship, the relay transponder may be used to track free vehicles, such as deep submersibles, from the surface. The relay transponder is positioned relative to an array of bottom-anchored acoustic transponders. It is interrogated acoustically from the surface ship; it then sequentially interrogates the bottom transponders which, in turn, reply to the ship. From the measurement of the total travel time (ship to relay transponder to bottom transponder to ship) and assuming, or knowing, the sound velocity of the water, we obtain a relayed range measurement. These relayed ranges, used in conjunction with ship to bottom-transponder ranges, allow us to calculate the position of the relay transponder. A recent application of this technique is described in which several gravity core samples from the crest of the Horizon Guyot were positioned with respect to the detailed bathymetry and the geology within the area. The estimated error in positioning the samples is less than 20 m inside a navigational net extending over 100 km2.

Improving Navigational Systems Through Establishment of a Marine Geodetic Range

POSITIONS OR DIRECTIONS in or on the deep oceans often cannot be determined with sufficient accuracy using ocean navigation systems now available. Present limitations on accuracy arise, in part, because of the lack of reliable marine reference systems, including permanent marine control points. Control points are needed of the type that permit such a high degree of accuracy in land positioning. The accuracy and reliability of marine navigation systems could be improved if variations from some known standard could be determined. This paper discusses a standard system that could be established, viz., a marine geodetic calibration range. Positional fixes made with present systems are sometimes a mile or more in error. These systems could be evaluated, calibrated, and compared using the suggested marine geodetic range as a standard. The systems could be adjusted to minimize errors, thereby improving their accuracy and reliability. In one possible form, a geodetically constructed calibration range could extend parallel to a portion of the U. S. continental shelf and seaward to about 1500 miles from shore. The range, based on a bottom-referenced system tied to the U. S. land geodetic network, might consist of a network of lines or grids formed, for example, by three to six permanent, and three temporary, ocean-bottom control points. In one configuration, identification of stations would be by acoustic signals tramsmitted by a set of three transponders on the sea bottom. Position on the ocean surface relative to the bottom transponders would be determined by solving a three-dimensional intersection problem, as is done in land geodesy. The most important measurements would be the line distances between the control points. It would be possible to measure these distances using aircraft line-crossing or satellite techniques. The final coordinates of the control points on the sea bottom could be determined (by applying geodetic adjustment procedures) only after distance measuremens were completed. The relative accuracy of the proposed calibration range would be equivalent to 1:200,000, or about ±50 feet along a 1500-mile calibration line.

Search Operations In the Thresher Area—1964 Section II

A three unit task group, USS HOIST, USNS MIZAR and Research Vehicle TRIESTE II, conducted tactical and technical development operations in the THRESHER loss area during the summer months 1964. A team of Naval Research Laboratory scientists constructed and operated a highly successful towed vehicle which obtained photographs of the majority of THRESHER hulk. MIZAR was the laboratory and tow ship for this effort. TRIESTE II suffered an unfortunate main motor fire and hence did not possess adequate mobility for satisfactory search performance. However, the NRL acoustic tracking system on MIZAR was able to provide a precise location on THRESHER wreckage and of TRIESTE relative to a bottom transponder. Consequently, TRIESTE II was directed to THRESHER hull and conducted a one hour close inspection (5–7 feet) of a portion of the hull. This paper is a summary of the 1964 operations with comments on operational problems and solutions by the Task Group Commander.

Search Operations In The Thresher Area – 1964 Section I

ABSTRACTA three unit task group, USS HOIST, USNS MIZAR and Research Vehicle TRIESTE II, conducted tactical and technical development operations in the THRESHER loss area during the summer months 1964. A team of Naval Research Laboratory scientists constructed and operated a highly successful towed vehicle which obtained photographs of the majority of THRESHER hulk. MIZAR was the laboratory and tow ship for this effort. TRIESTE II suffered an unfortunate main motor fire and hence did not possess adequate mobility for satisfactory search performance. However, the NRL acoustic tracking system on MIZAR was able to provide a precise location on THRESHER wreckage and of TRIESTE relative to a bottom transponder. Consequently, TRIESTE II was directed to THRESHER hull and conducted a one hour close inspection (5–7 feet) of a portion of the hull. This paper is a summary of the 1964 operations with comments on operational problems and solutions by the Task Group Commander.