TY - JOUR A1 - Tu, Rui T1 - Fast determination of displacement by PPP velocity estimation JF - Geophysical journal international N2 - Global Positioning System (GPS) has been proven to be an effective tool to retrieve high-precision displacement for the natural hazard monitoring. The network positioning and Precise Point Positioning (PPP) are the two basic approaches for its data solution, but the former one can only get a relative displacement within the local reference frame and requires a complex and continuously linked infrastructure, and the latter one with a long convergence time to obtain the absolute displacements within the global reference frame. To overcome these drawbacks, this paper proposed a method of fast determining the displacement by PPP velocity estimation (PPPVE). The key of the approach is that the velocity vector parameters are not correlated with other unknown parameters, such as ambiguities and atmosphere, so they can be fast and accurately estimated and integrated into displacements. The validation shows that the displacement can be provided with a precision of 1-2 cm in 1 min by PPPVE. In additional, the Kalman smoothing estimation can be used to improve the PPP solution. KW - Satellite geodesy KW - Space geodetic surveys KW - Earthquake ground motions Y1 - 2014 U6 - https://doi.org/10.1093/gji/ggt480 SN - 0956-540X SN - 1365-246X VL - 196 IS - 3 SP - 1397 EP - 1401 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Panet, Isabelle A1 - Kuroishi, Yuki A1 - Holschneider, Matthias T1 - Wavelet modelling of the gravity field by domain decomposition methods: an example over Japan JF - Geophysical journal international N2 - With the advent of satellite gravity, large gravity data sets of unprecedented quality at low and medium resolution become available. For local, high resolution field modelling, they need to be combined with the surface gravity data. Such models are then used for various applications, from the study of the Earth interior to the determination of oceanic currents. Here we show how to realize such a combination in a flexible way using spherical wavelets and applying a domain decomposition approach. This iterative method, based on the Schwarz algorithms, allows to split a large problem into smaller ones, and avoids the calculation of the entire normal system, which may be huge if high resolution is sought over wide areas. A subdomain is defined as the harmonic space spanned by a subset of the wavelet family. Based on the localization properties of the wavelets in space and frequency, we define hierarchical subdomains of wavelets at different scales. On each scale, blocks of subdomains are defined by using a tailored spatial splitting of the area. The data weighting and regularization are iteratively adjusted for the subdomains, which allows to handle heterogeneity in the data quality or the gravity variations. Different levels of approximations of the subdomains normals are also introduced, corresponding to building local averages of the data at different resolution levels. We first provide the theoretical background on domain decomposition methods. Then, we validate the method with synthetic data, considering two kinds of noise: white noise and coloured noise. We then apply the method to data over Japan, where we combine a satellite-based geopotential model, EIGEN-GL04S, and a local gravity model from a combination of land and marine gravity data and an altimetry-derived marine gravity model. A hybrid spherical harmonics/wavelet model of the geoid is obtained at about 15 km resolution and a corrector grid for the surface model is derived. KW - Wavelet transform KW - Satellite geodesy KW - Geopotential theory Y1 - 2011 U6 - https://doi.org/10.1111/j.1365-246X.2010.04840.x SN - 0956-540X VL - 184 IS - 1 SP - 203 EP - 219 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Hayn, Michael A1 - Panet, I. A1 - Diament, M. A1 - Holschneider, Matthias A1 - Mandea, Mioara A1 - Davaille, A. T1 - Wavelet-based directional analysis of the gravity field evidence for large-scale undulations JF - Geophysical journal international N2 - In the eighties, the analysis of satellite altimetry data leads to the major discovery of gravity lineations in the oceans, with wavelengths between 200 and 1400 km. While the existence of the 200 km scale undulations is widely accepted, undulations at scales larger than 400 km are still a matter of debate. In this paper, we revisit the topic of the large-scale geoid undulations over the oceans in the light of the satellite gravity data provided by the GRACE mission, considerably more precise than the altimetry data at wavelengths larger than 400 km. First, we develop a dedicated method of directional Poisson wavelet analysis on the sphere with significance testing, in order to detect and characterize directional structures in geophysical data on the sphere at different spatial scales. This method is particularly well suited for potential field analysis. We validate it on a series of synthetic tests, and then apply it to analyze recent gravity models, as well as a bathymetry data set independent from gravity. Our analysis confirms the existence of gravity undulations at large scale in the oceans, with characteristic scales between 600 and 2000 km. Their direction correlates well with present-day plate motion over the Pacific ocean, where they are particularly clear, and associated with a conjugate direction at 1500 km scale. A major finding is that the 2000 km scale geoid undulations dominate and had never been so clearly observed previously. This is due to the great precision of GRACE data at those wavelengths. Given the large scale of these undulations, they are most likely related to mantle processes. Taking into account observations and models from other geophysical information, as seismological tomography, convection and geochemical models and electrical conductivity in the mantle, we conceive that all these inputs indicate a directional fabric of the mantle flows at depth, reflecting how the history of subduction influences the organization of lower mantle upwellings. KW - Wavelet transform KW - Satellite geodesy KW - Gravity anomalies and Earth structure KW - Pacific Ocean Y1 - 2012 U6 - https://doi.org/10.1111/j.1365-246X.2012.05455.x SN - 0956-540X SN - 1365-246X VL - 189 IS - 3 SP - 1430 EP - 1456 PB - Oxford Univ. Press CY - Oxford ER -