Estimating and comparing dam deformation using classical and gnss techniques

Global Navigation Satellite Systems (GNSS) receivers are nowadays commonly used in monitoring applications, e.g., in estimating crustal and infrastructure displacements. This is basically due to the recent improvements in GNSS instruments and methodologies that allow high-precision positioning, 24 h availability and semiautomatic data processing. In this paper, GNSS-estimated displacements on a dam structure have been analyzed and compared with pendulum data. This study has been carried out for the Eleonora D'Arborea (Cantoniera) dam, which is in Sardinia. Time series of pendulum and GNSS over a time span of 2.5 years have been aligned so as to be comparable. Analytical models fitting these time series have been estimated and compared. Those models were able to properly fit pendulum data and GNSS data, with standard deviation of residuals smaller than one millimeter. These encouraging results led to the conclusion that GNSS technique can be profitably applied to dam monitoring allowing a denser description, both in space and time, of the dam displacements than the one based on pendulum observations

Covariance function modelling in local geodetic applications using the simplex method

Collocation has been widely applied in geodesy for estimating the gravity field of the Earth both locally and globally. Particularly, this is the standard geodetic method used to combine all the available data to get an integrated estimate of any functional of the anomalous potential T. The key point of the method is the definition of proper covariance functions of the data. Covariance function models have been proposed by many authors together with the related software. In this paper a new method for finding suitable covariance models has been devised. The covariance fitting problem is reduced to an optimization problem in Linear Programming and solved by using the Simplex Method. The procedure has been implemented in a FORTRAN95 software and has been tested on simulated and real data sets. These first tests proved that the proposed method is a reliable tool for estimating proper covariance function models to be used in the collocation procedure

Neutron activation analysis of archeological artifacts using the ISIS pulsed neutron source

Archeological artifacts can be analyzed after neutron irradiation at the pulsed ISIS neutron and muon source, UK, using a newly installed high purity germanium gamma ray spectrometer to perform neutron activation analysis. In this work, the details of the measurement methods and data analysis are presented. In particular, it is explained how Monte Carlo calculations are necessary to evaluate the detection efficiency, taking into account self-shielding effects. The results for two certified bronze standards are presented. The good agreement between expected and measured compositions is promising for the use of this technique for archeological artifacts where the elemental concentration is often unknown. As an example, the analysis of a Chinese sword from the first or second century BC is presented