Workflow for robust Scholte and Love waves phase-velocity estimation from small aperture Ocean Bottom Seismometer arrays in Lake Lucerne: deployment, location, orientation, and clock error correction

The phase-velocity dispersion curve (DC) is an important characteristic of the propagation of surface waves in sedimentary environments. Although the procedure for DC estimation in onshore environments using ambient vibration recordings is well established, the DC estimation in offshore environments using arrays of Ocean Bottom Seismometers (OBS) presents three main challenges. These are the localization, the orientation of the OBS horizontal components, and the clock error. Here, we concentrate on the workflow for a robust estimation of the phase-velocity dispersion curves from small aperture OBS array measurements in Lake Lucerne (Switzerland). OBS array campaigns were performed between 2018 and 2020 using arrays with a maximum aperture of 679 m at a maximum water depth of 81 m. The challenges related to the OBS location on the lake floor were addressed by combining the multibeam bathymetry map and the backscatter image for the investigated site with the differential GPS coordinates of the OBS at recovery. The OBS measurements were complemented by airgun surveys. Airgun data were first used to estimate the misorientation of the horizontal components of the OBS and second to estimate the clock error. Finally, we use two array processing methods, namely the three-component high-resolution frequency-wavenumber and the interferometric multichannel analysis of surface waves, to estimate the dispersion characteristics of the propagating surface waves for one of the array sites. We clearly observe the phase-velocity dispersion curve branches for Scholte and Love waves in the frequency range between 1.2 and 3.2 Hz for both array processing techniques.

Accuracy Evaluation of Broadcast Ephemeris for BDS-2 and BDS-3

The BDS-3 system was completed in July 2020 and began to provide services to users around the world. The inspection of its operation, especially the detailed evaluation of the orbit, clock error, TGD and other indicators, plays an important role in the subsequent positioning. This study conducts an investigation of the satellite broadcast ephemeris of the BDS-2 and BDS-3. The difference between the satellite orbit position calculated by the broadcast ephemeris and the position calculated by the precise ephemeris is used for analysis. First, the ephemeris form January 2020 to February 2020 are investigated. The results show that the broadcast ephemeris accuracy of the BDS-2 MEO satellite is the highest, while the GEO satellite broadcast ephemeris accuracy is the lowest. And their three-dimensional orbit difference is 3m and 7.5m, respectively. Second, the BDS-3 MEO satellite broadcast ephemeris accuracy is higher than the BDS-2, its three-dimensional orbit accuracy is about 0.39m, while its clock error is slightly smaller than the BDS-2. The result of ephemeris calculation is basically equivalent to the clock error of satellite-to-earth observation, which is related to the addition of the clock error of the inter-satellite link in the BDS-3. Finally, the clock error of the BDS-3 MEO satellite with the H clock is basically the same as that of the MEO satellite with the Rb clock.