Abstract
High-rate multi-constellation global navigation satellite system (GNSS) precise point positioning (PPP) has been recognized as an efficient and reliable technique for large earthquake monitoring. However, the displacements derived from PPP are often overwhelmed by the centimeter-level noise, therefore they are usually unable to detect slight deformations which could provide new findings for geophysics. In this paper, Global Positioning System (GPS), GLObalnaya NAvigatsionnaya Sputnikovaya Sistema (GLONASS), and BeiDou navigation satellite system (BDS) data collected during the 2017 Mw 6.5 Jiuzhaigou earthquake were used to further exploit the capability of BDS-only and multi-GNSS PPP in deformation monitoring by applying sidereal filtering (SF) in the observation domain. The equation that unifies the residuals for the uncombined and undifferenced (UCUD) PPP solution on different frequencies was derived, which could greatly reduce the complexity of data processing. An unanticipated long-term periodic error term of up to ± 3 cm was found in the phase residuals associated with BDS satellites in geostationary Earth orbit (GEO), which is not due to multipath originated from the ground but is in fact satellite dependent. The period of this error is mainly longer than 2000 s and cannot be alleviated by using multi-GNSS. Compared with solutions without sidereal filtering, the application of the SF approach dramatically improves the positioning precision with respect to the weekly averaged positioning solution, by 75.2%, 42.8%, and 56.7% to 2.00, 2.23, and 5.58 cm in the case of BDS-only PPP in the east, north, and up components, respectively, and 71.2%, 27.7%, and 37.9% to 1.25, 0.81, and 3.79 cm in the case of GPS/GLONASS/BDS combined PPP, respectively. The GPS/GLONASS/BDS combined solutions augmented by the SF successfully suppress the GNSS noise, which contributes to the detection of the true seismic signal and is beneficial to the pre- and post-seismic signal analysis.
Highlights
High-rate global navigation satellite systems (GNSSs) have shown great potential in observing both ground static and dynamic motions, which is more than a favorable complement to traditional seismometers [1,2]
The limitation is, that only relative displacement can be obtained with respect to the reference station, which might itself be subject to shaking in the case of a large earthquake
Based on the above analysis, this paper aimed to exploit high-rate multi-GNSS observations to improve the precision of displacement estimates, especially in the case of BeiDou navigation satellite system (BDS)
Summary
High-rate global navigation satellite systems (GNSSs) have shown great potential in observing both ground static and dynamic motions, which is more than a favorable complement to traditional seismometers [1,2]. The limitation is, that only relative displacement can be obtained with respect to the reference station, which might itself be subject to shaking in the case of a large earthquake. Compared with the traditional ionosphere-free combination PPP, the uncombined and undifferenced (UCUD) PPP using raw observations can retain all meaningful information and be extended to multi-frequency processing. It is a popularly adopted PPP model [11,12]. The high-rate PPP has the capability of generating kinematic position estimates at millimeter level if it is only quantifying a short period of data under favorable observation circumstances [13,14]. The 3-D displacement estimate is believed to have an accuracy of a few to ten centimeters, which hinders deep insights into rupture processes as well as possible geophysics findings
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