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. 2017 Jun 8;17(6):1324.
doi: 10.3390/s17061324.

Calibration of Magnetometers with GNSS Receivers and Magnetometer-Aided GNSS Ambiguity Fixing

Patrick Henkel  1
Affiliations

Calibration of Magnetometers with GNSS Receivers and Magnetometer-Aided GNSS Ambiguity Fixing

Patrick Henkel. Sensors (Basel). .

Abstract

Magnetometers provide compass information, and are widely used for navigation, orientation and alignment of objects. As magnetometers are affected by sensor biases and eventually by systematic distortions of the Earth magnetic field, a calibration is needed. In this paper, a method for calibration of magnetometers with three Global Navigation Satellite System (GNSS) receivers is presented. We perform a least-squares estimation of the magnetic flux and sensor biases using GNSS-based attitude information. The attitude is obtained from the relative positions between the GNSS receivers in the North-East-Down coordinate frame and prior knowledge of these relative positions in the platform's coordinate frame. The relative positions and integer ambiguities of the periodic carrier phase measurements are determined with an integer least-squares estimation using an integer decorrelation and sequential tree search. Prior knowledge on the relative positions is used to increase the success rate of ambiguity fixing. We have validated the proposed method with low-cost magnetometers and GNSS receivers on a vehicle in a test drive. The calibration enabled a consistent heading determination with an accuracy of five degrees. This precise magnetometer-based attitude information allows an instantaneous GNSS integer ambiguity fixing.

Keywords: attitude determination; calibration; carrier phase; magnetometer; satellite navigation.

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Conflict of interest statement

The author declares no conflict of interest.

Figures

Figure 1
Figure 1
Integer ambiguity fixing: sequential tree search with attitude constraints.
Figure 2
Figure 2
Benefit of magnetometer-based prior attitude information for single epoch integer ambiguity fixing: the accuracy of the prior heading information is shown on the x-axis and the accuracy of the prior pitch information is provided in the legend.
Figure 3
Figure 3
Benefit of magnetometer-based prior attitude information for single epoch integer ambiguity fixing: the probability varies over time due to the changing satellite constellation.
Figure 4
Figure 4
Maps with track of vehicle, split into two processing steps.
Figure 5
Figure 5
Magnetic flux measurements in sensor-fixed frames: the measured magnetic flux in x- and y- directions depends on the heading and is quite noisy. The least-squares estimate of the magnetic flux is much less noisy, as the estimation combines the measurements from 40 s to determine the 3D magnitude of the magnetic flux and the 3D biases.
Figure 6
Figure 6
Heading determination with calibrated magnetometer in comparison to tightly-coupled GNSS/INS heading: the latter one has an accuracy of 0.25 degrees and serves as a reference. As the magnetometer-based heading is noisy, a filtered version with a time constant of 0.1 s is also shown.
Figure 7
Figure 7
Detailed analysis of heading performance for two sections with moderate to high rotational dynamics: the filtered magnetometer-based heading deviates by less than 10 degrees from the GNSS/INS tightly coupled heading.
See this image and copyright information in PMC

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