We present an enhanced multiposition method (EMM) to suppress the north finding error caused by bias drift with fiber optic gyroscopes (FOGs). The new proposal is a static method to find the true north, and it employs a differential strategy and a rotation scheme of increasing step angle. Using the noise model of Allan variance, we analyze the north finding errors caused by angle random walk (ARW), rate random walk (RRW), and rate ramp (RR) theoretically, where RRW and RR are two main noise sources of bias drift, and ARW is the rate white noise. Theoretical analysis indicates that, in the traditional multiposition method (TMM), as the position number increases, the error caused by ARW decreases while that by bias drift increases. Therefore, the suppressions of ARW and bias drift are conflicted with each other. The north finding accuracy is limited by bias drift. In contrast, in EMM, both errors caused by ARW and bias drift will decrease as the position number increases. Experimental results with two specific FOGs verify our theoretical analysis. In our experiments, we study the effect of position number and step angle on the north finding accuracy. Utilizing the proposed EMM, for FOG-1, the north finding error has been reduced by 76.60%, and for FOG-2, a 36.33% reduction has been achieved. Our proposal provides a more effective and stable way to find true north, and it can also be applied to other rate gyroscopes.
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