North seeker is widely used in military and civil orientation. It can determine the north in static all-weather, all-round, fast and real-time, so as to determine the carrier azimuth, that is, the Angle between a reference axis of the carrier and the true north direction, to be used as the azimuth reference for observation, target targeting and navigation system reset, and also as the azimuth reference for underground operations such as tunnels and mines. In military applications, gyroscopic north seeker is especially required to achieve fast and accurate orientation in a short period of time. However, due to the influence of environmental interference factors such as wind gust, vehicle engine operation, human movement and temperature change, the output of gyroscope contains not only useful signals of earth rotation, but also drift signals of different components, which will seriously affect the orientation accuracy of the system. Therefore, effectively eliminating gyro drift is the key to ensure the precision of north seeking.

For random drift that can not be compensated by simple methods, most of the filtering methods are used to remove the interference noise. The traditional denoising methods are mostly linear filtering, which not only removes the noise, but also makes the abrupt point of the signal fuzzy. The median filtering method is a nonlinear processing method, which can ensure the satisfactory recovery of the signal's mutation point under certain conditions, but the median filtering only has a good filtering effect on pulse noise, while the suppression ability of random noise is not ideal. In order to overcome the low universality of traditional denoising methods, a denoising method based on wavelet transform is proposed. The wavelet threshold denoising method is widely used in the wavelet domain, which is suitable for the analysis of signals with low frequency and high frequency at the same time, but it is only suitable for white noise and broadband noise, and it is powerless for pulse noise.

In order to better remove the noise in the gyro signal, we use the threshold method in the wavelet domain to filter out the white noise in the gyro signal, and use median filtering to filter out the impulse noise in the signal. The results of north-seeking experiments show that this method is effective and feasible in removing this kind of noise.

The full article: https://www.ericcointernational.com/application/application-of-wavelet-domain-median-filter-in-north-seeker.html
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