Communications – electrical: acoustic wave systems and devices – Distance or direction finding – With towing
Reexamination Certificate
2000-06-23
2001-07-03
Lobo, Ian J. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Distance or direction finding
With towing
C367S124000, C367S131000
Reexamination Certificate
active
06256264
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains generally to a device for accurate estimation of an underwater towed vehicle's position, and more particularly to the making of an estimate of an underwater towed vehicle's position independent of off-board sensors and horizontal range from the towing vehicle.
2. Description of the Prior Art
Underwater towed vehicles are in common use for surveying and location of objects in the ocean due to their relatively low operational cost. To be useful however, the position of the towed vehicle must be known so that the data collected by the towed vehicle's sensors may be geo-rectified. Due to currents in the water and the cantilever in the towing cable, a towed vehicle's position relative to the towing vessel is not easily determined. Since the ocean is opaque to high-frequency electromagnetic signals, the global positioning system (GPS) cannot be used for tow vehicle position.
Current methods for determining the position of a towed vehicle include the lay-back model (See, FIG.
1
), the long-base line (LBL) (See, FIG.
2
), the short base line (SBL) (See, FIG.
3
), and the inverted SBL systems. With the lay-back model method the towed vehicle is assumed to be directly behind the towing vehicle and the lay-back (distance from the towing vehicle) is assumed to be a fixed multiple of the tow vehicle's depth. Alternatively, the amount of cable paid out is assumed to be the slant range to the tow vehicle. The latter method does not take into account the cable's cantilever. Neither method takes into account the effects of local currents on the cables' shape and position. The accuracy of these methods will in general not support precise positioning of the towed vehicle.
The LBL method uses a series of acoustic transponders to localize the tow-vehicle by measuring the time delays between the tow-vehicle and the transponders. These transponders may be bottom mounted or located on the surface, such as shown in U.S. Pat. No. 5,119,341. While these systems are very accurate, their deployment is a time consuming and expensive operation. Furthermore, the LBL method requires that the system be redeployed to each operational area.
The SBL method uses time delay and measured arrival angle of an acoustic signal from the tow-vehicle to the towing vehicle to compute position. These systems are fairly accurate but their resolution is range dependent. Typically, in order to achieve sufficient accuracy, a SBL system is deployed over the tow-vehicle, requiring a second surface craft—an obvious economic disadvantage.
With the inverted SBL method, the directional acoustic receiver is mounted on the towed vehicle instead of the towing vehicle. As a consequence the range dependent accuracy of this system is a problem for very deep tows. SBL and inverted SBL systems cannot be readily used in applications with helicopter towed systems.
SUMMARY OF THE INVENTION
The object of this invention is to provide a system and method for accurate determination of an underwater towed vehicle's position.
Another object of the invention is to provide a system with a position accuracy that is not dependent upon the horizontal range of the towed vehicle from its host.
Another object of the invention is to provide a system where no off-board sensors are required and the system needs not be re-deployed in each new operation area.
Another object of the invention is to provide a system that is cheaper than existing systems.
These and other objectives are achieved with a device for localization of a submerged tow vehicle (LOST) that provides a technique for accurately determining the position of an underwater vehicle towed by a surface craft or a helicopter. The LOST system comprises a state updater, a maximum likelihood estimator, a constrained adaptive tracker and a slant range corrector. The state updater generates a prediction of the towed vehicle's position using a previous estimate and the towing vehicle's course and speed (i.e., dead rckoning). The maximum likelihood estimator utilizes the output of the state updater, along with the measured ocean depth at the current position of the towed vehicle and bathymetry data for the area to compute the most likely position of the towed vehicle based on ocean depth. The constrained adaptive tracker constrains the output of the maximum likelihood estimator by applying limits to the towed vehicle's velocity and acceleration. The slant range corrector forces the position estimate from the constrained adaptive tracker to have the proper slant range between the towed vehicle and a known reference point.
REFERENCES:
patent: 3860900 (1975-01-01), Scudder
patent: 4559621 (1985-12-01), Delignieres
patent: 4635236 (1987-01-01), Roberts
patent: 4924446 (1990-05-01), Cyr
patent: 5119341 (1992-06-01), Youngberg
patent: 6028823 (2000-02-01), Vincent et al.
Beckman; Location of Submerged Towfish (Lost); Master's Thesis; 2000 Tulane University.
Beckman Richard R.
Bourgeois Brian S.
Martinez Andrew B.
Karasek John J.
Legg Lawrence G.
Lobo Ian J.
The United States of America as represented by the Secretary of
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