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US4335433A
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Method for correcting navigation errors due to water currents
Assignee: United States Department of the Navy
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Filing: 1980-06-16
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Granted: 1982-06-15
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Expires: 2000-06-16
Abstract
Abstract In a satellite navigation system for an ocean vessel, a major source of error is unknown ocean currents when the navigation is done by dead-reckoning with respect to the waters. The present method for determining and correcting for ocean navigation error which is caused by unknown ocean currents provides a highly accurate position of the vessel with respect to the earth. The position error reflects not only the difference between a dead-reckoned position and a satellite fix position which up-dates the dead-reckoned position but also accounts for the motion of the vessel due to the ocean currents during the time between the satellite lock-on and the actual error computation and correction.
Inventors
- 👤 Russell H. Bauer
- 👤 Madeleine Heidkamp
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 04:06
CPC Classifications
G; G01; G01C; G01C21/00; G01C21/20; G01C21/203
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
151 words
In a system having a satellite fix position determining means and a dead-reckoning means for continuously estimating position between satellite fixes, a method for correcting ocean vessel navigation errors due to essentially constant water currents, comprising the steps of: periodically locking on to a satellite and determining present vessel position in latitude (φ F .sbsb.2) and longitude (λ F .sbsb.2) using satellite fixes at lock-on, comparing satellite fix latitude (φ F .sbsb.2) and longitude (λ F .sbsb.2) with dead-reckoned latitude (φ DR ) and longitude (λ DR ), respectively, at the time of fix to yield update corrections in latitude (φ u ) and in longitude (λ u ), defining differential functions (A ij ) which relate respective changes in current satellite fix position in latitude (φ F .sbsb.2) and longitude (λ F .sbsb.2) to respective changes in velocity in the north (v N ) and east (v E ) directions,
Claim 2
Dependent Claim
151 words
In a system having a satellite fix position determining means and a dead-reckoning means for continuously estimating position between satellite fixes, a method for correcting ocean vessel navigation errors due to essentially constant water currents, comprising the steps of: periodically locking on to a satellite and determining present vessel position in latitude (φ F .sbsb.2) and longitude (λ F .sbsb.2) using satellite fixes at lock-on, comparing satellite fix latitude (φ F .sbsb.2) and longitude (λ F .sbsb.2) with dead-reckoned latitude (φ DR ) and longitude (λ DR ), respectively, at the time of fix to yield update corrections in latitude (φ u ) and in longitude (λ u ), defining differential functions (A ij ) which relate respective changes in current satellite fix position in latitude (φ F .sbsb.2) and longitude (λ F .sbsb.2) to respective changes in velocity in the north (v N ) and east (v E ) directions,
Claim 3
Dependent Claim
132 words
partially predicting satellite fix errors in latitude (φ E ) and longitude (λ E ) at current and previous satellite updates as a function of the velocity changes (v N and v E ) and the differential functions (A ij ), determining the values for the differential functions A ij , comprising the steps of introducing known velocity errors in the north and east directions and measuring variations in satellite fix latitude (φ F .sbsb.2) and longitude (λ F .sbsb.2) positions resulting from the introduced known velocity errors, measuring the time (T) between satellite updates, and determining the velocity north and velocity east errors (v N and v E ) as a function of: time between satellite updates, update corrections (φ u and λ u ), and differential functions (A ij ).
Claim 4
Dependent Claim
132 words
partially predicting satellite fix errors in latitude (φ E ) and longitude (λ E ) at current and previous satellite updates as a function of the velocity changes (v N and v E ) and the differential functions (A ij ), determining the values for the differential functions A ij , comprising the steps of introducing known velocity errors in the north and east directions and measuring variations in satellite fix latitude (φ F .sbsb.2) and longitude (λ F .sbsb.2) positions resulting from the introduced known velocity errors, measuring the time (T) between satellite updates, and determining the velocity north and velocity east errors (v N and v E ) as a function of: time between satellite updates, update corrections (φ u and λ u ), and differential functions (A ij ).
Claim 5
Dependent Claim
64 words
A method as in claim 1 wherein the determining of the velocity north error (v N ) and the velocity east error (v E ) comprises the step of: approximating v N to a value of φ u divided by the time τ between satellite fixes and approximating v E to a value of λ u divided by the time τ between satellite fixes.
Claim 6
Dependent Claim
50 words
A method as in claim 1 wherein the function determining the velocity north error (v N ) and velocity east error (v E ) is: ##EQU3## and where τ is the time between successive satellite fixes and where A ij ' corresponds to A ij at the previous satellite fix.
Claim 7
Dependent Claim
114 words
A method as in claim 2 or 3 comprising the further step of: removing a position error buildup due to the velocity errors v N and v E comprising the step of: altering the dead-reckoned latitude and longitude positions φ DR and λ DR , with φ DR and λ DR defined as: ##EQU4## where φ DR ' and λ DR ' are the previous dead-reckoned latitude positions; A.sub.11 =∂φ.sub.F.sbsb.2 /∂v.sub.N A.sub.12 =∂φ.sub.F.sbsb.2 /∂v.sub.E A.sub.21 =∂λ.sub.F.sbsb.2 /∂v.sub.N A.sub.22 =∂λ.sub.F.sbsb.2 /∂v.sub.E comprise the A ij functions; RNAV is the distance to the center of the earth; and TSLLK represents the time between the satellite lock-on and the time when the position error buildup is removed.
Claim 8
Dependent Claim
73 words
A method as in claim 4 comprising the further steps of: storing previous water velocities X' and Y' in the north and east directions, respectively, subtracting the velocity north error (v N ) from the previous north water velocity (X') and subtracting the velocity east error (v E ) from the previous east water velocity (Y'), and vectorially combining the two difference values to provide a present water velocity output v w .
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1985-06-14 | 1985-12-14 | 1986-06-15 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1989-06-14 | 1989-12-14 | 1990-06-15 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1993-06-14 | 1993-12-14 | 1994-06-15 | $7700.00 | Window Closed / Lapsed |