Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Earth science
Reexamination Certificate
1999-10-14
2001-07-03
Oda, Christine (Department: 2862)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Earth science
C702S016000
Reexamination Certificate
active
06256585
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to hydrographic surveys and is directed more particularly to a method for determining on a continuous basis, the height of water above a chart datum as a survey vessel performs hydrographic surveys in a waterway, to provide more accurate depth data.
2. Description of the Prior Art
The traditional method of coastal hydrographic surveying relies on a tide gauge, i.e., a water level gauge. The tide gauge records water heights at a selected specified time interval, usually 6 or 10 minutes. A tide staff and a human recorder may also be used to record the tide at the selected specified time interval. The time indexed tide is subtracted from time indexed soundings to provide data for bathymetric maps, or nautical charts.
Tide (coastal projects) and stage (river projects) are vertical measurements relative to a specific water level in a navigation channel. Typically, the vertical reference is a low water event in order to maintain the minimum depth capable of transporting a vessel safely to port. The vertical measurements are recorded by a tide gauge at a specific period of time. Since the number of gauges are limited, water levels are modeled from the gauge, up and downstream, at a distance from the gauge. These modeled water levels, called “Tidal Zoning” are used to reduce soundings measured in a channel to a common reference, or chart datum. The problem with this approach is the use of averaged parameters. The parameters are “time” and “height” change at a distance from the gauge. Wind and changes in atmospheric pressure disrupt the average ambient conditions which, in turn, cause the models to provide false water level relationships during a hydrographic survey. Hydrographic surveys relative to a tide gauge develop ever increasing errors as the survey vessel travels away from the tide gauge. The disparities are of greater magnitude in areas that have a large range of tide.
Vessels maneuvering through a waterway typically use acoustic transducer depth-determining devices in an effort to ascertain hull clearance above a channel bottom. Unfortunately, the configuration and depth of the channel bottom varies because of shoaling. To compensate for vagaries in channel bottom depths, vessels frequently are loaded short of a full load to allow for a higher vessel bottom position above the channel bottom.
Accordingly, there is a need for improved vertical position data for vessels traversing waterways, so as to facilitate more accurate hydrographic surveys, which will produce more accurate indications onboard waterborne vessels as to the clearance beneath the keel of the vessel to the published channel depth.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a method for consistently providing hydrographic survey results.
A further object of the invention is to provide a method for more accurately determining, on a continuing basis, clearance between the bottom of a waterborne vessel and the bottom of a waterway thereunder, such that the vessel may be loaded for disposition closer to the clearance limits of the waterway.
With the above and other objects in view, as will hereinafter appear, a feature of the present invention is the provision of a method for plotting depths of a waterway, the method comprising the steps of determining nautical chart vertical reference values along a selected waterway, building a data base of the reference values and storing the data base in a computer accessible from a vessel traversing the waterway, and providing Global Positioning System (GPS) equipment accessible from the vessel and a radio receiver onboard the vehicle. The method further comprises operating the GPS equipment to continuously obtain positions of the vessel horizontally, operating the radio receiver and computer in conjunction with the GPS equipment to continuously obtain tidal data from the data base, and computations as to depth of the vessel beneath the vertical reference value, and plotting the depth data on a nautical chart.
In accordance with a further feature of the invention, there is provided a method for determining keel clearance of a waterborne vessel traversing a waterway, the method comprising the steps of providing a data base of tidal datum measurements and storing the data base in a computer accessible from the vessel, providing GPS equipment accessible from the vessel and a radio receiver onboard the vessel, operating the GPS equipment to continuously obtain positions of the vessel horizontally, and operating the radio receiver and computer in conjunction with the GPS equipment to continuously obtain the tide at the vessel's position in the waterway.
In accordance with a further feature of the invention, there is provided a method for providing a data base of nautical chart vertical reference values along the waterway and storing the data base in a computer accessible from the vessel, providing a radio receiver onboard the vessel and GPS equipment accessible from the vessel, operating the GPS equipment to continuously obtain positions of the vessel horizontally, operating the radio receiver and computer in conjunction with the GPS equipment to continuously obtain tidal data from the data base, and subtracting the draft of the vessel plus antenna height above waterline to obtain below keel clearance of the vessel relative to the chart datum.
In accordance with a still further feature of the invention, there is provided a method for determining vertical positions of a waterborne vessel's waterline above the chart datum at the vessel's present horizontal location in a waterway, the method comprising the steps of determining nautical chart vertical reference values along a selected waterway, building a data base of the reference values and storing the data base in a computer accessible from the vessel, providing GPS equipment accessible from the vessel, and a radio receiver onboard the vessel and adapted to receive kinematic carrier GPS corrections, and operating the computer, the GPS equipment, and the radio receiver, to continuously obtain data on current horizontal and vertical positions of the vessel.
The above and other features of the invention, including various novel details of combinations of steps, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method embodying the invention is shown by way of illustration only and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.
REFERENCES:
patent: 5323322 (1994-06-01), Mueller et al.
patent: 5386368 (1995-01-01), Knight
patent: 5452216 (1995-09-01), Mounce
patent: 5689475 (1997-11-01), Chaumet-Lagrange
patent: 5884213 (1999-03-01), Carlson
patent: 5884219 (1999-03-01), Curtwright et al.
patent: 5933110 (1999-08-01), Tang et al.
MacEvoy John
Oda Christine
Taylor Victor J.
U.S. Army Corps of Engineers as represented by the Secretary of
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