Stochastic modeling of high-stability ground clocks in GPS analysis

In current global positioning system (GPS) applications, receiver clocks are typically estimated epoch-wise in the data analyses even for clocks with high performance like Hydrogen-masers (H-maser). Applying an appropriate clock model for high-stability receiver clocks should, in view of the strong correlation between the station height and the clock parameters, significantly improve the positioning results. Recent experiments have shown that modeling the deterministic behavior of high-quality receiver clocks can improve the kinematic precise point positioning considerably. In this paper, well-behaving ground clocks are studied in detail applying constraints between subsequent and near-subsequent clock parameters. The influence of different weights for these relative clock constraints on the positioning quality, especially on the height, is investigated. For excellent clocks, an improvement of up to a factor of 3 can be obtained for the repeatability of the kinematic height estimates. This may be essential to detect small but sudden changes in the vertical component (e.g., caused by earthquakes). Troposphere zenith path delays (ZPD) are also heavily correlated with the receiver clock estimates and station heights. All these parameters are usually estimated simultaneously. We show that the use of relative clock constraints allows for a higher time resolution of the ZPD estimates (smaller than 2h) without compromising the quality of the kinematic height estimate

Consistency of PPP GPS and strong-motion records: case study of Mw9.0 Tohoku-Oki 2011 earthquake

GPS and strong-motion sensors are broadly used for the monitoring of structural health and Earth surface motions, focusing on response of structures, earthquake characterization and rupture modeling. Several studies have shown the consistency of the two data sets within at certain frequency (e.g., 0.03<f<0.2Hz). The compatibility of Precise Point Positioning (PPP) GPS and strong-motion data was assessed by comparing their respective displacement waveforms for several frequency bands (f<0.3Hz). For this purpose, there are used GPS and strong-motion records of the Mw9.0 Tohoku 2011 earthquake at 23 very close spaced sites and conclude that the agreement between the two datasets depends on the frequency of the excitation, the direction of the excitation signal and the distance from the excitation source

Lithosphere strain rate and stress field orientations near the Alpine arc in Switzerland

In this study we test whether principal components of the strain rate and stress tensors align within Switzerland. We find that 1) Helvetic Nappes line (HNL) is the relevant tectonic boundary to define different domains of crustal stress/surface strain rates orientations and 2) orientations of T- axes (of moment tensor solutions) and long-term asthenosphere cumulative finite strain (from SKS shear wave splitting) are consistent at the scale of the Alpine arc in Switzerland. At a more local scale, we find that seismic activity and surface deformation are in agreement but in three regions (Basel, Swiss Jura and Ticino); possibly because of the low levels of deformation and/or seismicity. In the Basel area, deep seismicity exists while surface deformation is absent. In the Ticino and the Swiss Jura, where seismic activity is close to absent, surface deformation is detected at a level of ~2 10E-8/yr (~6.3 10E-16/s)

Analysis of 1-Hz GPS data for the estimation of long-period surface motion of Tohoku-Oki Mw9.0 2011 earthquake

The GPS displacement time series are today mostly used for the estimation of the transient (period <2sec) and coseismic (static) displacement of an earthquake, while the estimation of the velocity and acceleration is based only seismic networks. In this study, we examine whether the GPS records can be used to capture the spectral characteristics of the long-period signal and their consistency with the corresponding seismic motion sensors, for the displacement, velocity and acceleration. For this purpose, we use the 1-Hz GPS network records of the Tohoku-Oki 2011 earthquake processed in Precise Point Positioning (PPP). The derived GPS and strong-motion waveforms were analysed resulting into displacement, velocity and acceleration for periods ranging from 3 to 100s. The derived GPS and strong-motion time series were compared and it was found that these are of similar pattern and amplitude. However, there is a non-constant phase shift between the corresponding GPS and strong-motion time series, resulting in significant difference between the time series in the time domain. On the contrary in the frequency domain, the GPS and strong-motion time series are consistent for periods larger than 3-4s. Finally the GPS and the strong-motion records were compared in the time-frequency domain based on wavelet analysis, revealing that both GPS and seismic records express consistently the variation of the long-period of the seismic signal. Thus, it is proved that the GPS records can be used for the estimation of the long-period ground motion and contribute to the reliable estimation of the corresponding characteristics (displacement, velocity, acceleration)

Analysis of 1-Hz GPS data for the estimation of long-period surface motion of Tohoku-Oki Mw9.0 2011 earthquake

The GPS displacement time series are today mostly used for the estimation of the transient (period <2sec) and coseismic (static) displacement of an earthquake, while the estimation of the velocity and acceleration is based only seismic networks. In this study, we examine whether the GPS records can be used to capture the spectral characteristics of the long-period signal and their consistency with the corresponding seismic motion sensors, for the displacement, velocity and acceleration. For this purpose, we use the 1-Hz GPS network records of the Tohoku-Oki 2011 earthquake processed in Precise Point Positioning (PPP). The derived GPS and strong-motion waveforms were analysed resulting into displacement, velocity and acceleration for periods ranging from 3 to 100s. The derived GPS and strong-motion time series were compared and it was found that these are of similar pattern and amplitude. However, there is a non-constant phase shift between the corresponding GPS and strong-motion time series, resulting in significant difference between the time series in the time domain. On the contrary in the frequency domain, the GPS and strong-motion time series are consistent for periods larger than 3-4s. Finally the GPS and the strong-motion records were compared in the time-frequency domain based on wavelet analysis, revealing that both GPS and seismic records express consistently the variation of the long-period of the seismic signal. Thus, it is proved that the GPS records can be used for the estimation of the long-period ground motion and contribute to the reliable estimation of the corresponding characteristics (displacement, velocity, acceleration)

CubETH: low cost GNSS space experiment for precise orbit determination

CubETH is a project to evaluate and demonstrate possibilities of low-cost GNSS receivers on a nano-satellite by following the Cubesat standard. The development of this new Swiss cubesat mission is underway at the Swiss Polytechnical Schools, launch is planned for 2016. Scientific goal are: precise orbit determination and estimate of satellite attitude based on a very short baseline together with a number of other experimental measurements. Programmatic goal is to implement this project in cooperation between federal (ETH/EPF domain) and cantonal (FH/HES domain) engineering schools and industrial partners. The educational objective is to involve engineering students from various schools across Switzerland to promote innovative teaching of engineering of complex systems. In this paper, we will discuss performance requirements for the CubETH spacecraft and its payload. We also show how lessons learned from the Swisscube satellite were used for the design and implementation of this project