Distributed Geocomputations and Web Collaboration
With the new Cyberinfrastructure available to the scientific community, advanced geocomputations are often distributed and with Virtual Globes, Observatories and HUBs, the environment is most conducive to web collaboration. Remote sensors can be networked using the web facilities and observational data analyzed from the desks of scientists in practically any location around the world. This is especially important in such fields as astronomy, geophysics and environmental science which have observatories and sensor instrumentation most often in remote locations. Examples of web networks will be described with some of the computational challenges for geoscientists. In particular, the Turtle Mountain Monitoring Project and Field Laboratory in South-Western Alberta will be briefly discussed. With the semantic web and related developments, scientific knowledge is going to benefit from such web collaboration in ways unheard of only a few years ago.
3-D Finite-Element Modelling of Magnetotelluric Data With a Static Divergence Correction
In the magnetotelluric method measurements are made of the electric and magnetic fields that are generated by electric currents induced in the Earth's subsurface by the naturally occurring time variations of the Earth's magnetic field. The induced currents, and hence the measured electric and magnetic fields, depend on the electrical conductivities of the geological structures in the subsurface. The most common technique for computing magnetotelluric data for a given 3-D Earth model is the finite-difference method. This has been applied to the second-order partial differential equations for the E-field and the H-field. In both cases it was found that a static divergence correction term greatly increased the efficiency of the solution procedure. Recently the finite-element method has been receiving attention as a means of modelling magnetotelluric data. The usual implementation of this method involves a discretization of the E-field in terms of edge-element basis functions. Because these basis functions preserve the continuity of the tangential component of the E- field between cells, it was thought that a static divergence correction like that for the finite-difference method was not necessary. However, this is not the case. A static divergence correction term, which is the gradient of a scalar potential calculated by solving a finite-element discretization of the direct-current resistivity differential equation, and which is the finite-element equivalent of the correction term developed for the finite-difference solution procedures, significantly accelerates 3-D finite-element magnetotelluric modelling.
The Role of Multi-Dimensional Wavelet Approximation in Geodetic Applications: De- Noising, Compression and Analysis Tool
The Singular Spectrum Analysis Approach in the Analysis of Weekly GRACE and Hydrology Models Water Mass Anomalies Information
We use the method of singular spectrum analysis to extract short- and long-term periodic water mass anomaly signals from a time series of the recently publicly available GFZ weekly GRACE solutions. We analyze time- lagged continuous time series (from February 2004 to May 2008) of GRACE spherical harmonic coefficients of maximum degree and order 30. One of the main advantages of performing the analysis in the spectral domain instead of in the spatial domain is the reduction of the computational load because a much smaller number of coefficients than spatial pixels are analyzed. Furthermore, no de-striping and isotropic smoothing filters are necessary because our filtering technique is able to smooth significantly the GRACE random errors and to reduce largely the correlated errors besides extracting all significant periodic signals. Moreover, the removal of part of geophysical signals together with the correlated GRACE errors and the reduction of the GRACE-derived water mass anomaly amplitudes are avoided. We demonstrate that our filtering technique effectively reduces the average RMS of water mass variability over the oceans when all but annual, semi-annual and long-term global variations in the spherical harmonic coefficients are filtered out. On land, we compare the filtered weekly GRACE-derived water mass anomalies with the weekly-averaged GLDAS mass anomalies for Amazon, Congo, Ob and Mississippi basins. The GRACE-derived trends agree well with the GLDAS model trends in all of the studied basins. Our results also demonstrate that the singular spectrum analysis approach is a powerful tool for extracting any short- and long-term signals as well as phase shifts and amplitude variations of the periodic water mass anomalies.
On Monte Carlo Methods and Applications in Geoscience
Monte Carlo methods are designed to study various deterministic problems using probabilistic approaches, and with computer simulations to explore much wider possibilities for the different algorithms. Pseudo- Random Number Generators (PRNGs) are based on linear congruences of some large prime numbers, while Quasi-Random Number Generators (QRNGs) provide low discrepancy sequences, both of which giving uniformly distributed numbers in (0,1). Chaotic Random Number Generators (CRNGs) give sequences of 'random numbers' satisfying some prescribed probabilistic density, often denser around the two corners of interval (0,1), but transforming this type of density to a uniform one is usually possible. Markov Chain Monte Carlo (MCMC), as indicated by its name, is associated with Markov Chain simulations. Basic descriptions of these random number generators will be given, and a comparative analysis of these four methods will be included based on their efficiencies and other characteristics. Some applications in geoscience using Monte Carlo simulations will be described, and a comparison of these algorithms will also be included with some concluding remarks.
Evaluation of Interpolators for Void Filling of Geophysical data sets
The use of Wavelets in GPS Error Analysis with Emphasis to Singularity Detection and Multipath Removal.