Aiming at the problem that the abnormal values of the measurement noise appear when GPS signals become weak or disappear in the urban environment, which reduces the positioning accuracy of the INS/GPS tight coupled navigation system, an improved adaptive filtering algorithm based on the adjustable Student-t distribution is proposed. This method uses Student-t distribution to model the measurement noise, the Mahalanobis distance of innovation vector to adjust filter’s adaptation, and the variational Bayesian method to better track changes in measurement noises. Experimental results show that the method can achieve a more robust estimation result and a better positioning effect in an urban environment.
We propose an improved optical coherence domain polarimetry (OCDP) calibration scheme by using polarization mode crosstalk (PMC). The scheme can be used to calibrate the OCDP system's measurement result about intensity of PMC. The intensity of 1st order PMCs are measured by polarization extinction ratio (PER) meter as the scale to transfer the standard into OCDP system, and the higher order PMCs formed by 1st orders are used to expand the scale. Specifying alignment angle of joint points and analyzer, we successfully use 3rd order PMCs and expand the range of calibration over -100 dB.
The stray interference peaks (SIPs) are an important factor resulting in the misjudgment of measurement information in white light interferometer (WLI). SIPs are generated by the residual reflected light beams. We theoretically analyze the interference conditions of the SIP. The analysis shows that these SIPs are discrete main interference peak outside and have different orders. We present a stagger optical path (SOP) method for suppressing or eliminating these SIP which will appear in the interference pattern. The SOP means that there is an appropriate fiber length determined by the delay amount of delay line between each joint. Moreover, an experiment with two joints, for simplicity, is given as an example. Experimental results show that the high-order SIP from the joints can be suppressed by the SOP to obtain a clean interference pattern.
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