Mazzoni, Augusto

The activities for establishing the Italian Reference Gravity Network started in 2022. This is in line with the actions promoted by the International Association of Geodesy that during its 2015 General Assembly approved a resolution on the establishment of the new global gravity network the so-called International Terrestrial Gravity Reference System/Frame that will replace IGSN71. An initial set of 30 stations has been defined over the peninsular part of Italy and the two main islands of Sicily and Sardinia. Particularly, the GGOS core station of Matera (the Agenzia Spaziale Italiana Center for Space Geodesy “Bepi” Colombo) is one of the network points as required in the documents of the GGOS-Bureau of Networks and Observations. Thus, this station will provide one link between the Italian national absolute gravity network and the GGOS observation system of IAG. In order to ensure the measurements traceability, as required by the international standards on gravity measurements, the absolute gravimeters used in the measurements participated in international comparison campaigns. Absolute gravity measurements have been supplemented with direct measurements of the local value of the vertical gravity gradient, in order to reduce the absolute values, measured by different instruments at different heights, to an intermediate and common reference height and to the ground reference level to transport it to an external associated station. The gravity field campaigns have been assisted by topographic survey campaigns, allowing a centimetric georeferencing of the gravity stations to the current ITRF. The collected data will be then validated and reduced following the internationally accepted standards and finally published through a dedicate web page of the project. These data will also be submitted to the absolute gravity database maintained by the Bureau Gravimétrique International/Bundesamt fuer Kartographie und Geodaesie where the absolute gravity data that will contribute to the new global absolute gravity reference system are collected.

In this poster we present the realization and the surveys performed to establish a new reference gravity and elevation network in Sicily with the aim to provide new reference systems useful for all the scientific and technological activities related to the gravity field and to the proper definition of a modern height system in this region. This network belongs to the under construction new Italian Reference Gravity Network (G0) that is part of the INGV Project Pianeta Dinamico, Task S2, during the period 2019-2022. The Sicilian network encloses 5 stations (Catania, Centuripe, Milazzo, Noto, and Palermo), evenly distributed forming a large mesh network which roughly covers the entire Sicily (Fig.1). All absolute stations are hosted inside structures that guarantee protection for the instrumentation during the measurements and the necessary power supply. In addition to the absolute gravity value, at each station, the vertical gravity gradient and the gravity difference (Δg) between the indoor absolute gravity and an outdoor satellite station were also measured. Gravity measurements were carried out between the end of 2021 and the 2022 with the Microg LaCoste FG5#238 and the Scintrex CG-6 gravimeters for absolute and relative measurements, respectively. Gravity data have been corrected for known effects ensuring the reliability and accuracy at the µGal level. The coordinates and the orthometric heights were at the same time measured with mixed terrestrial and satellite local networks at each site. The precise coordinates obtained after the adjustments were useful to post-process the absolute gravity data and to refer all the gravity measurements presented in this work to the equipotential surface of the gravity field. Since three of the five selected stations were measured in the past, it was also possible to evaluate the long-term stability of the gravity values at these stations.

In this paper we describe all the field operations and the robust post-processing procedures to determine the height of the new absolute gravimetric station purposely selected to belong to a new absolute gravimetric network and located in the Science Faculty of the L’Aquila University (Italy). This site has been realized indoor in the Geomagnetism laboratory, so that the height cannot be measured directly, but linking it to the GNSS antenna of AQUI benchmark located on the roof of the same building, by a classical topographic survey. After the topographic survey, the estimated height difference between AQUI and the absolute gravimetric site AQUIg is 14.970 ± 0.003 m. At the epoch of the 2018 gravimetric measurements, the height of AQUI GNSS station was 712.974 ± 0.003 m, therefore the estimated ellipsoidal height of the gravimetric site at the epoch of gravity measurements is 698.004 ± 0.005 m. Absolute gravity measurements are referred to the equipotential surface of gravity field, so that the knowledge of the geoidal undulation at AQUIg allows us to infer the orthometric height as 649.32 m.

The goal of this article is the illustration of the new functionalities of the VADASE (Variometric Approach for Displacements Analysis Stand-alone Engine) processing approach. VADASE was presented in previous works as an approach able to estimate in real time the velocities and displacements in a global reference frame (ITRF), using high-rate (1 Hz or more) carrier phase observations and broadcast products (orbits, clocks) collected by a stand-alone GNSS receiver, achieving a displacements accuracy within 1–2 cm (usually better) over intervals up to a few minutes. It has been well known since the very first implementation and testing of VADASE that the estimated displacements might be impacted by two different effects: spurious spikes in the velocities due to outliers (consequently, displacements, obtained through velocities integration, are severely corrupted) and trends in the displacements time series, mainly due to broadcast orbit and clock errors. Two strategies are herein introduced, respectively based on Leave-One-Out cross-validation (VADASE-LOO) for a receiver autonomous outlier detection, and on a network augmentation strategy to filter common trends out (A-VADASE); they are combined (first, VADASE-LOO; second, A-VADASE) for a complete solution. Moreover, starting from this VADASE improved solution, an additional strategy is proposed to estimate in real time the overall coseismic displacement occurring at each GNSS receiver. New VADASE advances are successfully applied to the GPS data collected during the recent three strong earthquakes that occurred in Central Italy on 24 August and 26 and 30 October 2016, and the results are herein presented and discussed. The VADASE real-time estimated coseismic displacements are compared to the static ones derived from the daily solutions obtained within the standard post-processing procedure by the Istituto Nazionale di Geofisica e Vulcanologia.

The knowledge of coseismic deformations due to earthquakes represents the fundamentals on which studies on seismic cycle and fault source mechanism are based on. Geodetic methods, in particular the recent developments of GNSS monitoring, are the only onescapable of providing the displacements of reference sites due to the occurrence of significant seismic events. Usually the detection of seismic offsets is done by comparing coordinates estimated before and after the earthquake. Here, considering the test case of the 30 October, 2016 central Italy seismic event, we show that it is possible to achieve such offsets also in real-time through the application of the new functionalities of the VADASE (Variometric Approach for Displacements Analysis Stand-alone Engine) approach. The comparison between the seismic offsets coming from the two approaches (static and realtime) is shown and discussed; the mean overall agreement is at the level of about half centimetre.

This paper describes the activities carried out in order to estimate the distance traveled by the neutrinos beam between CERN and LNGS with an accuracy better than 1 meter. In particular, the distance between two fundamental points has been estimated: the start point at CERN (de ned as T-40-S-CERN) and the OPERA detector point (de ned as A1-9999). The measurements campaings, at CERN and at LNGS, were performed using both terrestrial and Global Positioning System (GPS) based geodetic techniques. The positions of the two fundamental points were estimated in a common reference frame through the processing of the collected observations. The resulting distance (730534.610 m) was estimated with an accuracy at the level of 20 cm, remarkably better than the stated limit.

The Colli Albani Volcano has recently developed particular interest in the geophysical community for some peculiar characteristics imputable to a recent residual volcanic activity, thus evidencing that it cannot be considered extinguished yet. On April 2006 an airborne laser scanning (ALS) survey of the Albano and Nemi craters has been carried out to obtain a high resolution digital terrain model (DTM) of the area. We have compared the accuracy of the ALS heights with those obtained by a fast GPS kinematic survey, obtaining maximum deviation within 50 cm. Then, we have integrated the ALS survey of the craters and the bathymetry of the Albano lake to achieve a complete DTM, useful for morphological studies. In addition, with a GNSS/RTK survey (July 2007) we have estimated the Albano and Nemi mean lake levels respectively at 288.16 m and 319.02 m (asl). Based on the integrated DTM and the newly estimated water level values, we have evaluated about 21.7 106 of m3 the water volume loss of the Albano lake from 1993 to 2007, with an average rate of about 1.6 106 m3/yr.

In April 2006 an airborne laser scanning (LIDAR) survey of the Albano and Nemi craters was carried out to obtain a high resolution digital terrain model (DTM) of the area. We have integrated the LIDAR survey of the craters and the recent bathymetry of the Albano lake to achieve a complete DTM, useful for morphological studies. In addition, with a GPS RTK survey (July 2007) we estimated the Albano and Nemi mean lake levels respectively at 288.16 m and 319.02 m (asl). Based on the integrated DTM and the newly estimated water level values, we evaluated about 21.7·106 m3 the water volume loss of the Albano lake from 1993 to 2007, with an average rate of about 1.6·106 m3/yr.