C. Sciarretta

Mantle viscosity inferences from joint inversions of pleistocene deglaciatio‐induced changes in geopotential with a new SLR analysis and polar wander

Joint inversions of post-glacial rebound-induced secular changes in low degree harmonics of the geopotential and true polar wander (TPW) systematically indicate that the upper mantle viscosity has a value that is considerably smaller than 10 21 Pas. The lower mantle viscosity is about one order of magnitude larger than the upper mantle viscosity. Discrepancies in the viscosity profiles inferred from even and odd zonals are likely an indication of recent, unmodeled glacial forcings and/or insufficient precision in the evaluation of the mass loss from Pleistocene ice sheets. The influence of systematic errors in SLR data reduction due to thermal drag on the LAGEOS satellites for the uneven zonals of the geopotential is avoided by making use of the Starlette and Stella satellites to recover the uneven zonals and by considering lumped coefficients for these uneven terms.

Geodetic control on recent tectonic movements in the central Mediterranean area

Abstract During the Neogene and Quaternary, the western Mediterranean geodynamics was apparently dominated by the nearly eastward migration of the Apenninic arc and the associated opening (spreading) of the back-arc basin (Tyrrhenian Sea). However, during the last 5 My, the collision of the arc with the Apulian platform led to a dramatic change in the tectonic setting of the area. As geological processes require a long period of time to register the displacements of the different blocks, it is indispensable to take into account the present-day motion given by space geodesy data analysis in order to better constrain the geological models. Geodetic motions were derived from Global Positioning System (GPS), Satellite Laser Ranging (SLR) and Very Long Baseline Interferometry (VLBI) observations collected from different networks. All the geodetic solutions have been computed and combined at the Centre of Space Geodesy (CGS), at Matera, Italy. The geodetic results show a NNE motion of the Adriatic plate with a small component of counter-clockwise rotation, in good agreement with the geological and geophysical observations. In the southern Tyrrhenian area, the lengthening of the Matera–Cagliari baseline should imply that convergence cannot be considered as the driving mechanism for the Apenninic subduction process. The estimated motion of Noto is in quite good agreement with the estimated motion of the African plate.

The SLR secular gravity variations and their impact on the inference of mantle rheology and lithospheric thickness

A long history of SLR (Satellite Laser Ranging) observations of the geodetic satellites LAGEOS-I, LAGEOS-II, Starlette and Stella have been analyzed in order to estimate the time series of the low degree zonal coefficients in the Earth gravity field, up to degree six, and derive their secular drifts. The paper will point out the critical aspects of the analysis process and will compare the estimated zonal rates with other published results. Comparison of these zonal rates with the results of global, viscoelastic Earth models forced by Pleistocenic deglaciation, shows that the SLR retrieved zonals and the lumped odd zonals can be used to infer the upper mantle viscosity and lithospheric thickness. Discrepancies in the viscosity profiles, required to reproduce the different zonals, seem to indicate ongoing mass redistribution over the Earth.

Comparison of atmospheric parameters derived from GPS, VLBI and a ground-based microwave radiometer in Italy

Abstract Integrated Precipitable Water Vapor (IPWV) derived from GPS, water vapor radiometer WVR-1100 and RAdiosonde OBservation (RAOB) have been compared for the Cagliari site (Italy) on a seasonal and annual bases. The comparison analysis on estimating IPWV among the three independent techniques (GPS, WVR-110 and RAOB) has shown high accuracy equal to 0.136 cm with a bias of −0.049 cm throughout 1999. Furthermore, a comparison has been made between the estimated atmospheric parameters, equivalent zenith tropospheric delay (ZTD) and horizontal gradient, as resulting from independent analyses of GPS and VLBI data for the three Italian collocated stations: Matera, Medicina and Noto. We have realized that VLBI ZTD estimates are lower than that obtained by GPS of about 1.0–1.5 cm, while the standard deviations range from 0.5 to 2.0 cm.

ESTIMATION OF LOW DEGREE GEOPOTENTIAL COEFFICIENTS USING SLR DATA

Abstract Geodetic satellites have been providing the low frequency part of the geopotential models used for precise orbit determination purposes (e.g. JGM3, EGM96, …). Nevertheless they can be used to estimate the temporal variation of selected coefficients, helping to clarify the complex interrelations in the earth-ocean-atmosphere system. In this paper we present the two years long analysis of SLR data from the seven available geodetic satellites (Lageos I–II, Stella, Starlette, Ajisai, Etalon I–II) to recover monthly estimates of low degree geopotential coefficients; the results are obtained analysing the satellites separately and in proper combination. An accurate modelling of the satellite orbits is required in order to separate the geopotential coefficients: we assume as a priori geopotential the JGM3 model together with its associated tides and we take care of non-gravitational effects on the satellites by means of proper empirical estimated accelerations. The time series of the estimated coefficients (J2, J3, J4, J5) are inspected to detect the sub-annual perturbations related to seasonal variation of mass distribution. Huge residual seasonal signals in the orbit of Stella indicate a strong model deficiency related to the Suns influence on the environment. The remaining six satellites are homogeneously modelled and build up a three cycles per year oscillation on J2 and a seasonal oscillation (1 year and six month periods) revealed on the J4. The origin and possible causes of these signals are further discussed in the text. We also present a preliminary J 2 estimate, using twelve years of Lageos-I and Lageos-II observations, that is compared with previous obtained values.

A contribution in the estimation of tectonic motion in crucial areas: the CGS96 SLR solution

Abstract The CGS96 is a global SLR solution based on the reduction of the whole available data set for the Lageos I and II satellites, starting from 1986. The accurate modelling adopted and the huge quantity of data of continuously growing quality, lead to reliable estimates of geodetic and orbital parameters. The solution collects a wide variety of parameters, daily earth orientation parameters, coordinates and site velocities of almost 60 sites, plus coordinates for sites with short tracking history, orbital parameters and non-modelled acceleration for both satellites. The core of the paper is the review of the tectonic results and their comparison with the models: the pointers of the goodness of the solution are those results regarding sites centrally located on the major plates, henceforth comparable to model predictions, being a prerequisite for the reliability of the estimates for the crucial sites. The tectonic results are particularly interesting in those areas not suitably described by the global models, such as the Mediterranean, periodically occupied by mobile systems.

GPS meteorology: validation and comparisons with ground-based microwave radiometer and mesoscale model for the Italian GPS permanent stations

Abstract Ground-based GPS meteorology has been developed during the last decade. Beside the GPS traditional application for precise geodesy, the GPS system has proved to be a powerful tool in atmospheric studies, such as climatology and meteorology. During 1999, at the Space Geodesy Center (CGS) of the Italian Space Agency (ASI) an operative and automatic system was developed in order to produce GPS tropospheric parameters on a daily basic for the Italian GPS permanent stations. In this work the operational processing of the GPS data is described. Moreover, the validation of the GPS tropospheric parameters through a comparison with other independent GPS solutions as well as independent techniques is presented. The GPS internal validation of zenith tropospheric delay (ZTD) shows a bias of 5 mm (absolute values) and a standard deviation ranging from 4 to 20 mm. For a few stations a comparison is performed between the GPS derived precipitable water vapor (PWV) and both the one computed using the MM5 and the one measured by the water vapor radiometer (WVR) and radiosondes (RAOB). The agreement between GPS and MM5 is within the range of 2–7 mm; for GPS, WVR and RAOB the standard deviation ranges from 0.85 to 1.62 mm.

The Italian GPS Fiducial Network: Services and products

Abstract Starting from 1995 new permanent GPS stations have been established in Italy to constitute the Italian GPS Fiducial Network (IGFN), together with the fundamental station in Matera. The present operational stations are: Cagliari, Matera, Medicina, Noto and Venezia, while a new station in Genova is under set-up. The whole data set acquired is collected at Matera Space Geodesy Center (CGS of the Italian Space Agency). Since August 1996, the Matera ASI/CGS has become EUREF Local Analysis Center, taking part in the IGS Pilot Project for densification of the ITRF through regional GPS analysis. The present ASI/CGS contribution consists of weekly solutions of 10 GPS sites providing the coordinates of the 5 stations of the IGFN (mentioned above) plus 5 foreign stations: Ebre, Madrid, San Fernando, Villafranco and Wettzell. In this paper a full description of all the services associated to the IGFN will be given and the results based on 10 months of continuous data analysis will be discussed. Furthermore future developments of the IGFN are outlined and possible applications in studies of regional deformations are shown.

Investigation on the combination of space geodetic techniques

Abstract The Space Geodesy Center (CGS) of the Italian Space Agency (ASI), located near Matera (Italy), hosts permanent Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR) and Global Positioning System (GPS) systems and manages the other receivers of the Italian GPS Fiducial Network. The presence of these collocated space geodetic systems in the area and the data analysis activities usually carried out at the CGS for each of the three techniques makes the construction of fully integrated solutions a natural objective. This paper describes the preliminary work carried out to assess the consistency of the various geodetic solutions and to explore their compatibility in order to combine the information content from the different techniques. The consistency of the CGS geodetic global solutions providing site positions and velocities is assessed, with particular attention to the Mediterranean and European areas. In addition a direct comparison between baselines and baseline rates for the collocated european GPS and VLBI sites is made.

A REVIEW OF SLR CONTRIBUTIONS TO GEOPHYSICS IN EURASIA BY CGS

In the past 30 years the Satellite Laser Ranging(SLR) technique has improved to a large extent, currently achieving a ranging precision down toa few millimeters. Moreover the growth in the size of the international network of SLR stations and therapidly growing constellation of geodetic target satellites make the SLR a well established technique for solidEarth studies and for the related Earth subsystem sciences. The long SLR observation history has become a veryimportant source of data for global and local changes detection and monitoring in many different fields.Tectonic plate motion, crustal deformation, post-glacial rebound and subsidence, Earth rotation, and polarmotion, time variations of the Earths gravitational field, ocean tides modeling, center of mass of the totalEarth system monitoring, International Terrestrial Reference System (ITRS) maintenance are only themain applications in which the SLR technique plays a significant role. Plate boundary zones in whichdeformation is diffuse are in general geographical areas associated with high seismic and volcanic activity.A principal key to understand the geophysics of a plate boundary process is the detailed knowledge of the3-D kinematics. This work will focus on the relevant results of the Eurasian SLR subnetwork in termsof technological evolution and crustal deformation. A general overview of the Eurasian SLR stationperformance will be presented with particular reference to the state-of-the-art SLR observatory MLRO (Matera LaserRanging Observatory). The current tectonic deformations (velocity and strain-rate field) detectedby the Eurasian network and by the former WEGENER/MEDLAS campaigns will also be discussed.