Effectiveness of observation-domain sidereal filtering for GPS precise point positioning

Abstract

Sidereal filtering is a technique used to reduce errors caused by multipath in the positioning of static receivers via the Global Positioning System (GPS). It relies upon the receiver and its surrounding environment remaining static from one day to the next and takes advantage of the approximately sidereal repeat time of the GPS constellation geometry. The repeating multipath error can thus be identified, usually in the position domain, and largely removed from the following day. We describe an observation-domain sidereal filter algorithm that operates on undifferenced ionospheric-free GPS carrier phase measurements to reduce errors caused by multipath. It is applied in the context of high-rate (1 Hz) precise point positioning of a static receiver. An observation-domain sidereal filter (ODSF) is able to account for the slightly different repeat times of each GPS satellite, unlike a position-domain sidereal filter (PDSF), and can hence be more effective at reducing high-frequency multipath error. Using 8-h long datasets of GPS measurements from two different receivers with different antenna types and contrasting environments, the ODSF algorithm is shown overall to yield a position time series 5-10 % more stable, in terms of Allan deviation, than a PDSF over nearly all time intervals below about 200 s in length. This may be particularly useful for earthquake and tsunami early warning systems where the accurate measurement of small displacements of the ground over the period of just a few minutes is crucial. However, the sidereal filters are also applied to a third dataset during which two short episodes of particularly high-frequency multipath error were identified. These two periods are analyzed in detail and illustrate the limitations of using sidereal filters with important implications for other methods of correcting for multipath at the observation level.

Performance of GPS sidereal filters during a satellite outage

“…This is what this article seeks to con rm by simulating prolonged satellite outages. This contrasts with Atkins and Ziebart (2016) where outages were not considered.…”

“…All these events have the potential to adversely a ect the performance of a conventional positiondomain sidereal lter (PDSF) which assumes that precisely the same combination of satellites is visible on adjacent days. It was mentioned in Atkins and Ziebart (2016) that an observation-domain sidereal lter (ODSF) should perform better in such circumstances. This is what this article seeks to con rm by simulating prolonged satellite outages.…”

Comparison of Three Methods for Estimating GPS Multipath Repeat Time

“…Previous studies did not adopt the data of satellites affected by orbit maneuvering in data processing (e.g., [6,9,11,13]). Choi et al [6] and Larson et al [8] used the mean MRT of the adopted satellites to implement sidereal filtering, and the effectiveness of multipath mitigation will get worse if the data of the affected satellites are included in their sidereal filtering.…”

“…Based on this time-domain repeatability, Bock et al [3,4] proposed a method named sidereal filtering to mitigate multipath error for static GPS positioning. Sidereal filtering has been well developed and widely applied (e.g., [5][6][7][8][9][10][11][12][13][14][15]). The general principle of sidereal filtering is the construction of a multipath correction model from the residuals of coordinates or observables of the previous day(s), then the correction of the data of the subsequent day(s) by subtracting the corresponding correction value for each epoch.…”

“…Then, we compare the performances of the three methods in multipath reduction after ASF corrections. The ASF is a modified sidereal filtering, which corrects the multipath of observables for each satellite with its MRT estimate [11,13].…”