Device and method for calibrating and improving the accuracy of barometric altimeters with GPS-derived altitudes

• US 7,429,948 B2
• Filed: 10/19/2006
• Issued: 09/30/2008
• Est. Priority Date: 04/12/2001
• Status: Expired due to Term

• Current Assignee: Garmin Limited
• Original Assignee: Garmin Limited
• Inventors: Oliver, Tracy, Burgett, Scott
• Primary Examiner(s): Gregory; Bernarr E
• Application Number:
  US11/551,180
• Publication Number:
  US 20070040732A1
• Time in Patent Office: 712 Days
• Field of Search: 738/652, 73384-387, 701/1, 701/3, 701/4, 701/7, 701/10, 702/85, 702/98, 702/127, 702/138, 342/118, 342/120, 342/121, 342/122, 342/165, 342173-175, 342/195, 34235701-35717
• US Class Current: 342/174
• CPC Class Codes: G01C 21/20 Instruments for performing navigational calculations G01C21/24, G01C21/26 take precedence
• CPC Class Codes: G01C 25/00 Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass testing, calibrating or compensating compasses G01C17/38
• CPC Class Codes: G01C 5/06 by using barometric means
• CPC Class Codes: G01S 19/14 specially adapted for specific applications
• CPC Class Codes: G01S 19/42 Determining position

Abstract

In a combined GPS/altimeter device, the calibration and hence the accuracy of barometric altimeter measurements are enhanced with the aid of derived altitudes from a GPS. The device determines the need for calibration and perform the subsequent computations necessary to facilitate the calibration. Furthermore, the device determines a correction quantity that should be applied to barometric altitude readings, thereby allowing the device to be calibrated while in motion. Both of these features ultimately result in a more accurate determination of altitude.

Claims

1. An altitude determining apparatus comprising:

an altimeter operable to determine an altitude of the apparatus;

a GPS unit for receiving satellite signals from a plurality of satellites and operable to determine an altitude of the apparatus;

a processor adapted to calibrate the altimeter accounting for changes in local atmospheric pressure when the altimeter and GPS unit are moved in tandem, wherein the processor calibrates the altimeter by subtracting the average difference between the altitude determined by the altimeter and the altitude determined by the GPS unit from the altitude as determined by the altimeter; and

a portable and handheld housing for housing the altimeter, the GPS unit, and the processor.

2. The apparatus as set forth in claim 1, wherein the processor calibrates the altimeter while the apparatus is in motion.

3. The apparatus as set forth in claim 1, wherein the processor continuously calibrates the altimeter.

4. The apparatus as set forth in claim 1, wherein the altimeter includes a barometric pressure sensor.

5. An altitude determining apparatus comprising:

an altimeter for determining a first altitude reading;

a GPS receiver for receiving satellite signals from a plurality of satellites; and

a processor coupled with the altimeter and the GPS receiver for calculating a second altitude reading as a function of the satellite signals, such that the processor is adapted to calibrate the altimeter while the apparatus is in motion by accounting for dynamic changes between the readings, wherein the processor determines an average altimeter drift for use in calibration.

6. The apparatus as set forth in claim 5, wherein the processor continuously calibrates the altimeter.

7. The apparatus as set forth in claim 5, wherein the altimeter includes a barometric pressure sensor.

8. The apparatus as set forth in claim 5, wherein the processor determines a difference in the altitude readings and subtracts the difference from the first reading.

9. The apparatus as set forth in claim 5, wherein the processor determines an average difference in the readings and subtracts the average difference from the first reading.

10. The apparatus as set forth in claim 5, wherein the altimeter, the GPS receiver, and the processor are housed in a portable and handheld housing.

11. An altitude determining apparatus comprising:

a barometric pressure sensor for determining a first altitude reading;

a GPS receiver for receiving satellite signals from a plurality of satellites; and

a processor coupled with the barometric pressure sensor and the GPS receiver for calculating a second altitude reading as a function of the satellite signals, such that the processor is adapted to calibrate the barometric pressure sensor accounting for changes in local atmospheric pressure while the apparatus is in motion using differences in the altitude readings, wherein the processor calibrates the barometric pressure sensor by subtracting the difference in the altitude readings from the first altitude.

12. The apparatus as set forth in claim 11, wherein the processor continuously calibrates the barometric pressure sensor.

13. The apparatus as set forth in claim 12, wherein the barometric pressure sensor, the GPS receiver, and the processor are housed in a portable and handheld housing.