Luca Vittuari

Geophysical survey at Talos Dome, East Antarctica: the search for a new deep-drilling site

Abstract Talos Dome is an ice dome on the edge of the East Antarctic plateau; because accumulation is higher here than in other domes of East Antarctica, the ice preserves a good geochemical and palaeoclimatic record. A new map of the Talos Dome area locates the dome summit using the global positioning system (GPS) (72˚47’ 14’’S, 159˚04’ 2’’ E; 2318.5m elevation (WGS84)). A surface strain network of nine stakes was measured using GPS. Data indicate that the stake closest to the summit moves south-southeast at a few cm a–1. The other stakes, located 8 km away, move up to 0.33ma–1. Airborne radar measurements indicate that the bedrock at the Talos Dome summit is about 400m in elevation, and that it is covered by about 1900 m of ice. Snow radar and GPS surveys show that internal layering is continuous and horizontal in the summit area (15 km radius). The depth distribution analysis of snow radar layers reveals that accumulation decreases downwind of the dome (north-northeast) and increases upwind (south-southwest). The palaeomorphology of the dome has changed during the past 500 years, probably due to variation in spatial distribution of snow accumulation, driven by wind sublimation. In order to calculate a preliminary age vs depth profile for Talos Dome, a simple one-dimensional steady-state model was formulated. This model predicts that the ice 100m above the bedrock may cover one glacial–interglacial period.

The potential of 3D techniques for Cultural Heritage object documentation

The generation of 3D models of objects has become an important research point in many fields of application like industrial inspection, robotics, navigation and body scanning. Recently the techniques for generating photo-textured 3D digital models have interested also the field of Cultural Heritage, due to their capability to combine high precision metrical information with a qualitative and photographic description of the objects. In fact this kind of product is a fundamental support for documentation, studying and restoration of works of art, until a production of replicas by fast prototyping techniques. Close-range photogrammetric techniques are nowadays more and more frequently used for the generation of precise 3D models. With the advent of automated procedures and fully digital products in the 1990s, it has become easier to use and cheaper, and nowadays a wide range of commercial software is available to calibrate, orient and reconstruct objects from images. This paper presents the complete process for the derivation of a photorealistic 3D model of an important basalt stela (about 70 x 60 x 25 cm) discovered in the archaeological site of Tilmen Höyük, in Turkey, dating back to 2nd mill. BC. We will report the modeling performed using passive and active sensors and the comparison of the achieved results.

A Comparative Study of the Applied Methods for Estimating Deflection of the Vertical in Terrestrial Geodetic Measurements

This paper compares three different methods capable of estimating the deflection of the vertical (DoV): one is based on the joint use of high precision spirit leveling and Global Navigation Satellite Systems (GNSS), a second uses astro-geodetic measurements and the third gravimetric geoid models. The working data sets refer to the geodetic International Terrestrial Reference Frame (ITRF) co-location sites of Medicina (Northern, Italy) and Noto (Sicily), these latter being excellent test beds for our investigations. The measurements were planned and realized to estimate the DoV with a level of precision comparable to the angular accuracy achievable in high precision network measured by modern high-end total stations. The three methods are in excellent agreement, with an operational supremacy of the astro-geodetic method, being faster and more precise than the others. The method that combines leveling and GNSS has slightly larger standard deviations; although well within the 1 arcsec level, which was assumed as threshold. Finally, the geoid model based method, whose 2.5 arcsec standard deviations exceed this threshold, is also statistically consistent with the others and should be used to determine the DoV components where local ad hoc measurements are lacking.

Monumentations of control points for the measurement of soil vertical movements and their interactions with ground water contents

Historically, one of the techniques used in the study of vertical movements of soil is that of high precision spirit levelling. Nowadays, this technique is often accomplished by satellite interferometric synthetic aperture radar (SAR) analysis that requires a calibration phase, i.e. through the connection to a spirit levelling network or by means of a long time series acquired by global navigation satellite systems permanent stations in order to transform relative velocities derived by SAR in absolute terms. An important aspect of this process consists of the materialization of the object used as a control point, while its selection may depend on the geological context. Typically, due to the inevitably high cost of installation, very accurate monumentation is reserved only for a limited density of points on the territory; therefore, a type of negative correlation exists, in terms of reliability in the monumentation of the control points, with respect to their density in a real distribution within a specific monitoring technique. For example, in levelling networks, a density of one benchmark every 700–1000 m of line is often desired in order to reach a compromise among costs, practical operative requirements and precision. Levelling benchmarks are usually fixed on existing structures (i.e. buildings or concrete structures). This aspect is even more evident in the case of SAR interferometric analysis, where the persistent scatterers (PS) are identified based on the coherence in the radar response. Therefore, the PS display movements are measured by a variety of different structures, characterized by foundations fixed at different depths. Starting from repeated levelling measurements, we verified the order of magnitude of movements of control points characterized by shallow foundations in cohesive soils. In practice, we observed their behaviour in relation to the depth of the foundation under simple and very common conditions, such as the presence of periods of drought or rainfall. The results indicate movements in the order of 3–7 mm in the first metre of depth that occurred in a week during the transition between the period of summer drought and the first rains. The magnitude of the total uplift observed between the end of the summer drought and the beginning of successive springtime (30/08/2012–18/04/2013) exceeded 10 cm of movement in very shallow layers of the soil surface for the same test field.

Integrated Use of Advanced InSAR and GPS Data for Subsidence Monitoring

Global Positioning Systems (GPS) and Advanced Synthetic Aperture Radar Interferometry (InSAR) are complementary monitoring techniques. Their integrated use allows to take advantage of the strengths offered by each approach, overcoming their weaknesses. The case study described in this paper presents an interesting integration methodology developed in order to study the subsidence phenomena at regional scale. Arpa (Regional Agency for Environmental Prevention), on behalf of the Emilia-Romagna Region and in collaboration with Tele-Rilevamento Europa) TRE. and the Department of Engineering of the Bologna University (DICAM), has recently updated the regional subsidence map of the Po Plain sector of the region, using the measurement of the vertical displacement obtained with the integrated use of continuous GPS stations and Advanced InSAR data. A SqueeSAR™ analysis of Radarsat radar images acquired between 2006 and 2011, was carried out over the whole regional plain territory, allowing to obtain a map of vertical displacement for more than 2,000,000 measurement points. In parallel, the acquired data from 17 permanent GPS stations were processed in order to calibrate and validate the InSAR results. The final calibrated results has permitted to obtain a complete and homogeneous map of the subsidence phenomena at regional scale, defining a both “absolute” and relative velocity datum with respect to the ITRF (International Terrestrial Reference Frame) and European Terrestrial Reference Frame (ETRF).

Italian geodetic network as reference frame for geodynamic purposes (Terra Nova Bay — Victoria Land — ANTARCTICA)

An Italian geodetic network has been monumented and surveyed using a GPS satellite technique several times since 1988. The network can be divided into a general network, or reference frame, and a detailed network, smaller than the general one, to control the crustal deformations of the Mt. Melbourne volcano area. Some experiments were carried out to study the effects of some possible causes of variation in the GPS reference system, interesting for geodynamic purposes. In particular, tests were made on the use of precise ephemeris instead of broadcasting and different GPS data processing software, Bernese v.4.0 and Geotracer v.2.25. In 1995–96 absolute positioning was made for the network reference station, with the satellite Doris system, and the ITRF co-ordinates were obtained to compare them with the same ITRF co-ordinates obtained using GPS international campaigns.

Comparison of COSMO-SkyMed and RADARSAT-2 offset tracking results on David-Drygalski glacier (Antarctica) surface velocities

This note is about the comparison of coregistration offset tracking velocities of a glacier obtained with SAR sensors characterized by different wavelengths and spatial resolutions: Cosmo-SkyMED (X band) and RADARSAT-2 (C band). The study area is represented by the initial part of the David Glacier, in Antarctica, which is the most important outlet glacier of Victoria Land. Particular attention has been devoted to understand the role of polarization and penetration depth of the incident wavelength, which represent key parameters in determining the effective incidence angle and so, for this reason, affecting also derived velocities. Further investigation is needed to complete this analysis, considering also geophysical data and tidal effects. In particular, we focused our attention on the initial portion of the David glacier, comprising the grounding line (which is the line where the glacier begins to be floating on the sea surface), represented in fig. 3 [1]. The processed dataset consists of four COSMO-SkyMed (in the following simply CSK) Stripmap scenes and two RADARSAT-2 scenes in quad polarization Wide Fine Beam mode, made available respectively by Italian and Canadian Spatial Agencies through the “COSMO-SkyMed/RADARSAT-2 Initiative Joint Announcement of Opportunity” (Proposal id 2873/5247).

The Medium- to Long-Term Effects of Soil Liquefaction in the Po Plain (Italy)

The 2012 Emilia seismic sequence has shed light on some unusual geomorphological processes and related landforms observed in the Po Plain between the provinces of Modena and Bologna, namely small-scale sinkhole formation, in a non-karstic setting. In some of the areas previously affected by sinkholes, during the Emilia earthquakes, widespread coseismic effects were observed, as soil liquefaction, sand venting and ground cracks. Before 2012, these effects have been seldom observed in the Po Plain, mainly because of moderate seismicity. Known historical earthquakes, or eventually older events, could have been the original triggering factor of liquefaction of susceptible soils at shallow depth and formation of dikes and sills, as precursors of future sinkholes. To test this model, data collection on boundary conditions and a number of further field experiments is ongoing. In particular, the research is focused on three main issues: the setup of a geological model of the area, taking into account structural a tectonic features; the analysis of surface displacements horizontal (geodynamic) and vertical displacements (natural and/or artificial subsidence) and their relationships with the development of sinkholes. This is performed through the exploitation of SAR interferometric data and GPS data; geological and geotechnical characterization of soils, through a number of continuous boreholes, trenches and CPT tests for building cross sections and 3D models of areas prone to sinkhole development. These pieces of information are used for set up a numerical model and simulating the process of sinkhole triggering ad evolution in the River Po alluvial plain.

Analysis of the Interaction Between Buried Pipelines and Slope Instability Phenomena

Economic and social integration across Europe requires secure lifelines, such as roads, railways and pipelines. Existing and planned lifelines may come across a large number of different natural and anthropic hazards. For instance, past catastrophic events have dramatically shown that steel pipelines may be highly vulnerable to permanent ground deformation due to earthquakes and landslides. Therefore, their behaviour when exposed to processes that can generate large displacement and strain (co-seismic deformation and faulting, liquefaction, earth and rock slides and flows, rock falls) needs to be assessed. In fact, and in particular if toxic and/or flammable materials are transported, structural damage with eventual leakage might result in a severe risks for both human life and the environment, with associated relevant economic costs. To such purpose, in this work, a methodology for the assessment, prevention and efficient management of geological risks, mainly landslides, in steel buried pipelines will be presented. The proposed procedure aims at reducing the risk of environmental disasters and the subsequent huge financial and environmental losses.

Airborne GPS Performance during a Photogrammetric Project

Preliminary results obtained from the analysis of GPS data collected during an airborne photogrammetric project conducted in 1996 over the Island of Vulcano are described. The objective of this study is to determine an optimal processing procedure for obtaining high accuraacy projection center positions for large scale aerial photography applications. GPS measurements were collected using a multi antenna configuration both on the aircraft and on the ground. The performance of standard software for OTF differential kinematic processing was evaluated. In order to use redundant information both rigorous combination of independently computed solutions and simultaneous adjustment of GPS observation from multiple reference stations and mobile receiver were performed. GPS-derived camera projection centers are compared to the results from a aerotriangulation adjustment results. The results indicate that the GPS data can be helpful to preserve the accuracy level when there is a lack of ground control points.