F. Vespe

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.

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.

Earth satellites and gravitomagnetic field

SummaryWe discuss the possibility of measuring the Lense-Thirring (LT) gravitomagnetic effect on a «test-particle», usinga) orbital elements other than the nodal longitude andb) existing or planned earth satellites and in particular laser-ranged satellites such as LAGEOS (hereafter, LAGEOS-I) LAGEOS-II and LAGEOS-III. Our conclusion is that, using the presently available satellites, the only orbital parameter suitable to measure the LT effect is the nodal longitude. Furthermore, existing or planned laser-ranged satellites, such as LAGEOS-I and LAGEOS-II, would not give enough information to measure the gravitomagnetic effect, unless a new satellite, such as LAGEOS-III, Ciufolini (1984), with inclinationsupplementary to that of LAGEOS-I, will be launched. For this purpose, we also discuss the orbital injection accuracy requirements for the LAGEOS-III satellite.

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.

X-SAR Cosmo-SkyMed mission and its scientific applications in the field of earth's observations: Some topics concerning the combinations of the observations achieved with other techniques

The Italian Space Agency (ASI Agenzia Spaziale Italiana) funded 27 scientific projects in the framework of COSMO-SkyMed (CSK) program. A subset of them focused on the improvements of the quality and quantity of information which can be extracted from X-SAR data if integrated with other independent techniques (GPS, data and imagery in other bands and wavelengths). The paper summarizes the results obtained from same of these projects and, in particular, regarding: the use of GPS observations and Numerical Weather Models (NWM) to remove atmospheric artifacts from InSAR imagery so improving the CSK potentialities in the field of topographic mapping; the integration of SAR data in X, L and C bands to improve snow cover monitoring and glaciers detection; the use of X-SAR data to retrieve rain precipitation and its validation with C-band radar observations; the improvements of the focusing techniques.

ROSA – The Italian Radio Occultation Mission Onboard the Indian OCEANSAT-2 Satellite

Within the next October 2008 the Indian satellite OCEANSAT-2 will be launched. This satellite is a follow-on mission to the first one which had a scatterometer and an Ocean Color Monitoring (OCM) instrument onboard both devoted to ocean investigation and applications (prediction of cyclone trajectory, fishery, coastal zone mapping, etc.). For the second mission the Italian Radio Occultation GPS receiver (ROSA) devoted to atmospheric investigation will be added to the two payloads. The ROSA payload was designed and developed for the retrieval of atmospheric pressure, temperature, and humidity profiles. Its performance and specifications will be described in the present paper. The Italian Space Agency (ASI) has promoted the ROSA receiver development to strengthen scientific activities as well as to provide end-user applications. In conclusion the paper highlights the radio occultation related activities in Italy targeted on the next OCEANSAT-2 space mission hosting the ROSA receiver.

GNSS Radio Occultations for Climate Applications: a Benchmark with Spaceborne Nadir Sounders

The FOURIER mission (Adriani et al. 2001) has been selected by the Italian Space Agency, together with other 4 projects, for a feasibility study. Within the current year one of these will be selected to fly within the next 4 years. The primary goal of FOURIER is the development of a systematic and objective observational test of the predictive capabilities of climate models, as proposed by Goody (1998). This requires long-term climate benchmark observations that differ from those presently available. High accuracy, demonstrable with respect to international standards, is the primary requirement. Other important features follow from this requirement. At least two types of space measurement satisfy these criteria: refractivity retrieved by GPS microwave occultation data; and calibrated, resolved, thermal radiances. In Fourier mission it is foreseen to put on board both a GPS-GLONASS receiver and a spectral radiometer (the Planetary Fourier Spectrometer —PFS-) to perform just such a test. In the paper will be discussed how to compare and validate data which will be obtained with both instruments for the future mission. Essentially the “main drawback” is that: while the PFS points to nadir direction, GNSS occultations are retrieved just along Earth grazing directions. So only the occultations that occur along the spacecraft velocity direction are selected and benchmarking for calibration purposes.

Improvements in Geodetic Surveying Using GNSS Radio Occultation Observations

The coordinates of a static Global Navigation Satellite System (GNSS) station placed on the ground are estimated together with the delay suffered by the incoming satellite signals through the atmosphere. The tropospheric delay (TD) is shaped as the product of the zenith total delay (ZTD) times a slant factor or mapping function (MF) depending on the sine of elevation angles. In processing chain ZTD is just estimated together with the coordinates; while the MF is modeled apart, in an independent way, by using atmospheric profiles retrieved with balloon observations (RAOB) as done for the Niell (1996) or provided by climate or Numerical Weather Prediction (NWP) models as in the Vienna MFs. The several space missions devoted to GNSS-RO (e.g. COSMIC-FORMOSAT, METOP, CHAMP, GRACE end others) are providing a huge amount of data which makes worthwhile to be attempted the reconstruction of a new mapping function (MTMF) based on such kind of data. First results have been achieved merging GNSS-RO data with model. The merging is made necessary because often the GNSS-RO profiles don’t reach the ground. The validation activity however has pointed out not meaningful improvements. Thus we have changed algorithms just to minimize the impact of external data provided by the model. We have performed of course comparisons and validation activities as already done, working with data of GNSS stations spread in the Mediterranean area. In particular formal errors and repeatability of ZTD, coordinates and baselines estimated with the MTMF will be compared with those achieved applying the Niell mapping function. In validation activities we have implemented new MTMFs in bernese software.