A New Method to Restrain Schuler Periodic Oscillation in Inertial Navigation System Based on Normal Time–Frequency Transform

The pure inertial navigation system (INS) contains three inherent periodic oscillations, namely, Schuler periodic oscillation (SPO, 84.4 min), Foucault periodic oscillation (FPO), and Earth periodic oscillation (EPO, 24 h), which can decrease the navigation accuracy, especially in long-term and low-velocity applications, such as ships and submarines. This article applies the inaction method (IM) to restrain SPO. Compared to external damping network technology (EDNT) and integrated navigation technology (INT), the IM is more independent, as it does not require auxiliary reference information. The IM is based on the so-called normal time–frequency transform (NTFT), and its uniqueness lies in recognizing and extracting instantaneous amplitude, frequency, and phase from a harmonic/quasi-harmonic signal directly and exactly. In this article, simulation data and experimental data are analyzed, and both show that the IM is effective. Moreover, the calculation results show that IM has wider applicability and higher stability than internal damping network technology (IDNT) and bandpass (BP) filtering. Compared to pure INS, the root mean square (rms) of the velocity error decreases significantly; the rmss of the latitude and longitude errors decrease as well. The IM can restrain SPO, and FPO is also restrained. However, the IM has no effect on the divergence of longitude error, and the edge effect is a drawback that needs to be addressed in the future.