Alessandra Borghi

Submillimeter Accuracy of InSAR Time Series: Experimental Validation

This paper presents the results of a blind experiment that is performed using two pairs of dihedral reflectors. The aim of the experiment was to demonstrate that interferometric synthetic aperture radar (InSAR) measurements can indeed allow a displacement time series estimation with submillimeter accuracy (both in horizontal and vertical directions), provided that the data are properly processed and the impact of in situ as well as atmospheric effects is minimized. One pair of dihedral reflectors was moved a few millimeters between SAR acquisitions, in the vertical and east-west (EW) directions, and the ground truth was compared with the InSAR data. The experiment was designed to allow a multiplatform and multigeometry analysis, i.e., each reflector was carefully pointed in order to be visible in both Envisat and Radarsat acquisitions. Moreover, two pairs of reflectors were used to allow the combination of data gathered along ascending and descending orbits. The standard deviation of the error is 0.75 mm in the vertical direction and 0.58 mm in the horizontal (EW) direction. GPS data were also collected during this experiment in order to cross-check the SAR results

Global to Local Moho Estimate Based on GOCE Geopotential Model and Local Gravity Data

Collocation approach has been applied to get a global Moho model in spherical approximation based on a GOCE geopotential model. A simple single layer model, with known density contrast, has been considered and a linearized relationship between the spherical harmonic coefficients of the anomalous potential and those of the Moho depth has been derived. This allows the covariance propagation from gravity to Moho depth. The derived covariance functions are then used in the collocation estimate of the global Moho depth. In order to be as close as possible to the considered model, reductions for the gravity signal related to topography/bathymetry have been applied. Simulated and real data tests have been performed and the obtained global solution has been compared with Moho estimates available in literature.

Block model versus thermomechanical model : new insights on the present-day regional deformation in the surroundings of the Calabrian Arc

Abstract A finite-element thermomechanical model is used to analyse present-day crustal deformation in the surroundings of the Calabrian Arc. The major structural complexities of the Tyrrhenian area are taken into account, along with the rheological properties of the rocks resulting from a thermal analysis. A comparison between the results obtained from a model composed of three wide rheologically uniform blocks and those obtained from the thermomechanical model allows us to better constrain the geophysical assumptions and shed light on the roles of the different active mechanisms acting in the Tyrrhenian. Our comparative analysis enlightens the crucial role played by lateral rheological heterogeneities when deformation is analysed at short wavelengths of a few hundred kilometres of the Tyrrhenian, driving the observed diffuse SW–NE extension within the regional context of active Africa–Eurasia convergence. Furthermore, a χ2 analysis based on comparisons with GPS data confirms the hypothesis that a significant part of the Africa–Eurasia convergence is absorbed through the Calabrian subduction.

GPS Permanent Network Solution: the Impact of Temporal Correlations

In this work we analysed the time series of daily solutions of 4 Italian GPS permanent stations with the aim of investigating the presence of temporal correlations and their impact on the estimation of weekly solution and velocity field precisions.

New Covariance Models for Local Applications of Collocation

The least-squares collocation method, used to predict or filter a signal, is based on the estimation of the empirical covariance function and the fitting of the empirical values with a proper model function. Generally, with the standard methods on the sphere, we reach a good fitting only up to the first zero of the empirical function. In this work we have investigated how much the collocation filtering is affected by a poor fitting of the empirical covariance.

Quasi-geoid estimations in South America

A report on quasi-geoid computations in South America, based on the existing gravity data base collected in the framework of the South America Gravity Project (SAGP) is presented. Two estimation methods will be described. One of these is the standard “remove-restore” technique. The gridding of the residual gravity values (i.e. free air gravity anomalies minus the global geopotential model and the terrain effect) has been performed using, with some Refsinements, the GEOGRID program of the GRAVSOFT package (Tscherning et al, 1994) and the residual quasi-geoid signal has been evaluated through the ID FFT approach (Haagmans et al., 1993) which allows a fast and rigorous computation of this component. The second approach is based on ID FFT method applied on mean Helmert’s gravity anomalies, having removed the low frequency components using EGM96 model up to degree 50.