Apparatus and method for determining pitch and azimuth from satellite signals

• US 6,211,821 B1
• Filed: 09/16/1999
• Issued: 04/03/2001
• Est. Priority Date: 09/16/1998
• Status: Expired due to Term

• Current Assignee: Novatel Incorporated (Hexagon AB)
• Original Assignee: Novatel Incorporated (Hexagon AB)
• Inventors: Ford, Thomas J.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Mull, Fred H.
• Application Number:
  US09/398,530
• Time in Patent Office: 565 Days
• Field of Search: 342/357.11
• US Class Current: 342/357.36
• CPC Class Codes: G01S 19/22 Multipath-related issues
• CPC Class Codes: G01S 19/55 Carrier phase ambiguity resolution; Floating ambiguity; LAMBDA [Least-squares AMBiguity Decorrelation Adjustment] method

Abstract

A navigational apparatus includes a receiver, two antennas, and a computational unit to receive satellite positional signals and provides corrected position, azimuth, and pitch readings. The computational unit: determines differences in the signal carrier measurements output by the receiver; rejects or accepts carrier ambiguity candidates based on predefined criteria; and estimates multipath on successive pairs of carrier observations to obtain the corrected readings.

Claims

1. A navigational apparatus suitable for use with a plurality of satellites, each satellite transmitting a positional signal, the signal being carrier modulated with code and date, said navigational device comprising:

a primary antenna for acquiring a set of primary positional signals from the plurality of satellites;

a secondary antenna disposed in fixed relationship to said primary antenna, said secondary antenna for acquiring a set of secondary positional signals from the plurality of satellites;

receiver means in electrical communication with at least one of said primary and secondary antennas, said receiver means for inputting at least one said set of primary or secondary positional signals and for outputting post-correlation data derived from said at least one set of primary or secondary positional signals;

means for deriving a carrier-to-noise ratio for each said positional signal from said post correlation data;

means for deriving multipath error estimates from said signal to noise ratios;

means for reducing carrier ambiguity sets according to pre-determined criteria;

means for deriving an azimuth or pitch estimate using said multipath error estimates to optimally generate an azimuth and pitch estimate.

2. The navigational apparatus of claim 1 wherein said post-correlation data comprises at least one member selected from the group consisting of single-difference observation and double-difference observation.

3. The navigational apparatus of claim 1 wherein said receiver means comprises a Global Positioning System receiver.

4. The navigational apparatus of claim 1 further comprising memory means.

5. The navigational apparatus of claim 1 further comprising a processing unit in electrical communication with said navigational apparatus and a magnetic sensor in electrical communication with said processing unit.

6. The navigational apparatus of claim 1 further comprising a second receiver means in electrical communication with the other of said primary and secondary antennas, said receiver means for inputting the other of said set of primary or secondary positional signals and for outputting post-correlation data derived from said other set of primary or secondary positional signals.

7. The navigational apparatus of claim 1 wherein said means for deriving a carrier-to-noise ratio comprises a computational device.

8. A method for deriving an attitude, pitch or positional reading for a vessel or flight vehicle from signals transmitted by a plurality of positional satellites, said method comprising the steps of:

acquiring a set of primary positional signals from the plurality of satellites via a primary antenna;

acquiring a set of secondary positional signals from the plurality of satellites via a secondary antenna;

deriving post-correlation data from said sets of primary and secondary positional signals;

deriving a signal-to-noise ratio for each said positional signal from said post correlation data;

deriving a multipath estimate from said signal to noise ratios; and

estimating an azimuth or pitch reading from said multipath estimate.

9. The method of claim 8 wherein said step of deriving a multipath estimate comprises a step of applying a Kalman filter.

10. The method of claim 8 further comprising the step of reducing carrier ambiguity sets in accordance with pre-determined criteria.

11. The method of claim 10 wherein said pre-determined criteria comprises at least one member of the group consisting of:

the size of a residual statistic compared to its expected value;

the size of a residual statistic compared to statistics for other ambiguity candidates; and

the degree of agreement that a computed baseline has with a baseline defined by the constraint values input by a user.

12. The method of claim 8 further comprising the step of calculating differential signal-to-noise ratios for each said positional signal.