AbstractThe noise level of kinematic Global Positioning System (GPS) coordinates is much higher than static daily coordinates. Therefore, it needs to be improved to capture details of small sub-daily tectonic deformation. Multipath is one of the dominant error sources of kinematic GPS, which the sidereal filter can mitigate. With increasing interest in applying kinematic GPS to early postseismic deformation studies, we investigate the characteristics of multipath errors and the performance of the position-domain sidereal filter using 30-s kinematic coordinates with a length of nearly 5 days. Experiments using three very short baselines mostly free from atmospheric disturbances show that multipath signature in position-domain has better repeatability at longer periods, and sidereal filtering without low-pass filtering yields a lift of power spectral density (PSD) at periods shorter than 200 s. These results recommend an empirical practice of low-pass filtering to a sidereal filter. However, a moderate cut-off period maximizes the performance of the sidereal filter because of the smaller multipath signature at longer periods. The amplitude of post-sidereal-filtered fluctuation is less than 6 mm in standard deviation, which demonstrates the nearly lowest noise level of kinematic GPS used for postseismic and other tectonic deformation studies. Our sidereal filter is proven to mitigate several peaks of power spectral density at periods up to 100,000 s, but the period dependency of PSD is not fully alleviated by sidereal filtering, which needs future investigation. Graphical Abstract