http://hdl.handle.net/2122/132 Ricerca nel canale cerca http://www.earth-prints.org/simple-search http://hdl.handle.net/2122/5891 Titolo: Radar systems for Glaciology<br/><br/>Autori: Zirizzotti, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Urbini, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Cafarella, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Baskaradas, J. A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia<br/><br/>Curatori: Kouemou, G.<br/><br/>Abstract: This chapter deals with radar systems, measurements and instrumentationemployed to study the internal core and bedrock of ice sheets in glaciology. The Earth's ice sheets are in Greenland and Antarctica. They cover about 10% of the land surface of the planet. The total accumulated ice comprises 90% of the global fresh water reserve. These ice sheets, associated with the ocean environment, provide a major heat sink which significantly modulates climate.Glaciology studies aim to understand the various process involved in the flow (dynamics), thermodynamics, and long-term behaviour of ice sheets.Studies of large ice masses are conducted in adverse environmental conditions (extreme cold, long periods of darkness). The development of remote sensing techniques have played an important role in obtaining useful results. The most widely used techniques are radar systems, employed sincethe 1950s in response to a need to provide a rapid and accurate method of measuring ice thickness. Year by year, polar research has become increasingly important because of global warming. Moreover, the discovery ofnumerous subglacial lake areas (water entrapped beneath the ice sheets) hasattracted scientific interest in the possible existence of water circulationbetween lakes or beneath the ice (Kapitsa et al., 2006; Wingham et al., 2006; Bell et al., 2007). Recent studies in radar signal shape and amplitude could provide evidence of water circulation below the ice (Carter 2007, Oswald and Gogineni 2008).In this chapter the radar systems employed in glaciology, radio echo sounding (RES), are briefly described with some interesting results. RES are active remote sensing systems that utilize electromagnetic waves that penetrate the ice. They are used to obtain information about the electromagnetic properties of different interfaces (for example rock-ice, ice-water, seawater-ice) that reflect the incoming signal back to the radar.RES systems are characterized by a high energy (peak power from 10 W to 10 KW) variable transmitted pulse width (about from 0.5 ns to several microseconds) in order to investigate bedrock characteristics even in the thickest zones of the ice sheets (4755 m is the deepest ice thickness measured in Antarctica using a RES system). Changing the pulse length or the transmitted signal frequencies it is possible to investigate particular ice sheet details with different resolution. Long pulses allows transmission of higher power than short pulses, penetrating the thickest parts of the icesheets but, as a consequence, resolution decreases. For example, the GPR system, commonly used in geophysics for rock, soil, ice, fresh water, pavement and structure characterization, employs a very short transmitted pulse (0.5 ns to 10 ns) that allow detailing of the shallow parts of an ice sheet (100-200 m in depth) (Reynolds 1997). Consequently, in recent years,GPR systems are also employed by explorers to find hidden crevasses on glaciers for safety. RES surveys have been widely employed in Antarctic ice sheet exploration andthey are still an indispensable tool for mapping bedrock morphologies and properties of the last unexplored continent on Earth. The advantage of using these remote sensing techniques is that they allow large areas to be covered, in good detail and in short times using platforms like aeroplanesand surface vehicles. http://hdl.handle.net/2122/5888 Titolo: La radiopropagazione nei ghiacciai<br/><br/>Autori: Bianchi, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Sciacca, U.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia<br/><br/>Abstract: Da alcuni anni l'INGV sta partecipando a progetti di ricerca nel campo della radioglaciologia, cioè lo studio dei ghiacciai tramite sistemi radar conosciuti anche come Radio Echo Sounding. Gli esiti del lavoro svolto in Istituto e i risultati delle campagne hanno portato alla pubblicazione di alcuni lavori, la formulazione dei quali ha richiesto lo svolgimento preventivo di considerazioni teoriche e l'approntamento di procedure di calibrazione. Queste considerazioni sono raccolte nel presente lavoro. http://hdl.handle.net/2122/4082 Titolo: Analysis of bottom morphology of the David Glacier-Drygalski Ice Tongue, East Antarctica<br/><br/>Autori: Tabacco, I. E.; Sezione Geofisica, Dipartimento di Science della Terra, Università degli Studi di Milano, I-20129 Milano, Italy; Bianchi, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Chiappini, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Zirizzotti, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Zuccheretti, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia<br/><br/>Abstract: Data from radio-sounding measurements have been analysed to determine the ice thickness and the bottom morphology of Drygalski Ice Tongue, Antarctica. The morphology and the structure of the bottom surface has been studied through an electromagneticinterpretation. A function that includes the gain/loss due to the geometrical shape of the reflecting surfaces has been calculated. Such a function has been evaluated assuming some physical electromagnetic quantities (the temperature of the glacier, the complex dielectric permittivity of ice, sea ice and sea water). The ice-water interface showsboth concave and convex faces toward the sounding system, producing a focusing or defocusing effect, detected as absolute (or relative) amplitude variation in the echo signal. It is shown that the calculated function follows quite well the observed bottom rippled surface of the glacier tongue estimated from the time-arrival measurements of the echo signal. http://hdl.handle.net/2122/4066 Titolo: Snow dunes and glazed surfaces in Antarctica: new field and remote-sensing data<br/><br/>Autori: Frezzotti, M.; ENEA, Centro Ricerche Casaccia, P.O. Box 2400, I-00100 Rome, Italy; Gandolfi, S.; DISTART, Università di Bologna, Viale Risorgimento 2, I-40136 Bologna, Italy; La Marca, F.; Dipartimento di ICMMPM, Università di Roma "La Sapienza", Via Eudossiana 18, I-00184 Rome, Italy; Urbini, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia<br/><br/>Abstract: As part of the International Trans-Antarctic Scientific Expedition project, the Italian Antarctic Programme undertook two traverses from the Terra Nova station to Talos Dome and to Dome C. Along the traverses, the party carried out several tasks (drilling, glaciological and geophysical exploration). The difference in spectral response between glazed surfaces and snow makes it simple to identify these areas on visible/near-infrared satellite images. Integration of field observation and remotely sensed data allows the description of different mega-morphologic features: wide glazed surfaces, sastrugy glazed surface fields, transverse dunes and megadunes. Topography global positioning system, ground penetrating radar and detailed snow-surface surveys have been carried out, providing new information about the formation and evolution of mega-morphologic features. The extensive presence, (up to 30%) of glazed surface caused by a long hiatus in accumulation, with an accumulation rate of nil or slightly negative, has a significant impact on the surface mass balance of a wide area of the interior part of East Antarctica. The aeolian processes creating these features have important implications for the selection of optimum sites for ice coring, because orographic variations of even a few metres per kilometre have a significant impact on the snow-accumulation process.Remote-sensing surveys of aeolian macro-morphology provide a proven, high-quality method for detailed mapping of the interior of the ice sheet's prevalent wind direction and could provide a relative indication of wind intensity. http://hdl.handle.net/2122/4063 Titolo: Evidence of 14 New Subglacial Lakes in the Dome C-Vostok Area<br/><br/>Autori: Tabacco, I. E.; Università degli Studi di Milano, Sezione Geofisica, Via Cicognara 7, 20129 Milano - Italy; Forieri, A.; Università degli Studi di Milano, Sezione Geofisica, Via Cicognara 7, 20129 Milano - Italy and Dipartimento di Scienze della Terra, Università di Siena, Via del Laterino 8, 53100 Siena - Italy; Della Vedova, A.; Università degli Studi di Milano, Sezione Geofisica, Via Cicognara 7, 20129 Milano - Italy; Zirizzotti, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Bianchi, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; De Michelis, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Passerini, A.; Università degli Studi di Milano Bicocca, Piazza della Scienza 1 , 20126 Milano - Italy<br/><br/>Curatori: Frezzotti, M.; ENEA Progetto Clima, PO Box 2400, 000100 Roma AD - Italy; Maggi, V.; Department of Environmental Sciences, University of Milano–Bicocca, Piazza della Scienza 1, I-20126 Milan, Italy<br/><br/>Abstract: In the last few years subglacial lakes have been of great interest to the scientific community for various reasons. The lakes could be an unknown extreme habitat, which have been isolated from the terrestrial biosphere for a long time. They may have formed before the ice sheet and could perhaps reveal environmental conditions prior to its formation. Lastly, they may play a role in the current dynamics of the ice sheet. Strong radar reflections from the base of the ice sheet can generally be ascribed to eitherwater-saturated basal sediments or subglacial lakes (Oswald & Robin, 1973). Based on radardata alone, the identification of lakes is possible if other features are present: flat and quite horizontal reflectors with nearly constant echo intensity and sharp edges similar to the margins of a catchment basin (Siegert et al., 1996; Siegert & Ridley, 1998; German & Siegert, 1999; Siegert, 2000; Tabacco et al., 2002). Subglacial lakes can be expressed in the overlying ice sheet as extremely flat surfaces with respect to the surrounding slopes (Ridley et al., 1993; Kapitsa et &l996 ; Siegert & Ridley,1998; Tabacco et al., 2002). To date, about 70 lakes have been discovered in all of Antarctica (Siegert et al.,1996); 21 of these are located in the Dome C-Vostok region. http://hdl.handle.net/2122/4062 Titolo: Reflecting Sub-Ice Surfaces Observed by Radio Echo Sounding System<br/><br/>Autori: Bianchi, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; De Michelis, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Sciacca, U.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Tabacco, I. E.; Università di Milano - Sezione Geofisica, Milano - Italy; Zirizzotti, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Zuccheretti, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia<br/><br/>Curatori: Frezzotti, M.; ENEA Progetto Clima, PO Box 2400, 000100 Roma AD - Italy; Maggi, V.; Department of Environmental Sciences, University of Milano–Bicocca, Piazza della Scienza 1, I-20126 Milan, Italy<br/><br/>Abstract: The reflection coefficient (R) at the interface of two media provides information on their electromagnetic nature. If the first medium is known, e.g. air (or ice, that in a broad interval of physical conditions maintains certain propagative characteristics nearly constant), the electromagnetic properties of the second medium can be determined. Hence, the ice/seawater,ice/water and ice/rock interfaces exhibit different reflection coefficients which can be detected by means of a RES system (Tabacco et al., 1999; Tabacco et al., 2000). The length of the radio wave does not allow the employment of sophisticated antennas, and so folded dipoles are arranged beneath the wings of the aircraft. As a consequence, the transmitted radio wave beam illuminates a relatively large area, and the power of the echo signal greatly depends on the shapeof the reflecting surfaces. An electromagnetic analysis shows that, in certain conditions, the variations in amplitude detected by the system are mainly due to focusing or defocusing effectsdetermined by the shape of the reflectors (Bianchi et al., 2001; Tabacco et al., 1999). http://hdl.handle.net/2122/4040 Titolo: Snow megadunes in Antarctica: Sedimentary structure and genesis<br/><br/>Autori: Frezzotti, M.; Ente per le Nuove Tecnologie, l’Energia e l’Ambiente, Roma, Italy; Gandolfi, S.; Dipartimento di Ingegneria delle Strutture, dei Trasporti, delle Acque, del Rilevamento, del Territorio, University of Bologna, Bologna, Italy; Urbini, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia<br/><br/>Abstract: Megadune fields occupy large areas in the interior of the East Antarctic ice sheet andare the result of unusual snow accumulation and redistribution processes. They thereforeare important to surface mass balance and ice core interpretation. Field observations (GPS,GPR, and surface measurements) have provided a detailed description of megadune sedimentation and morphology over a 70 km2 area, located 200 km east of Dome C. Acombination of remote sensing analysis (using Landsat and satellite radar altimetry) andfield measurements indicate that slope in the prevailing wind direction (SPWD) and climatic conditions play a crucial role in megadune genesis. The megadune areas tend to be characterized by slightly steeper regional slope and the presence of highly persistentkatabatic winds. The megadunes represent 2 to 4 m amplitude waves of 2 to 5 km wavelength formed by variable net accumulation, ranging between 25% (leeward faces) to 120% (windward faces) of the accumulation in adjacent nonmegadune areas. Leeward faces are characterized by glazed, sastrugi-free surfaces and extensive depth hoar formation. Windward faces are covered by large rough sastrugi up to 1.5 m in height. http://hdl.handle.net/2122/4008 Titolo: Italian RES Investigation in Antarctica: The New Radar System<br/><br/>Autori: Tabacco, I. E.; Dip. Scienze della Terra, Sez. Geofisica, Via Cicognara 2, Milano - Italy; Bianchi, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Baskaradas, J. A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Cafarella, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Sciacca, U.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Zirizzotti, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Zuccheretti, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia<br/><br/>Abstract: A Radio Echo Sounding (RES) system is an active remote-sensing instrument that uses electromagnetic wave penetration into the ice to obtain information on the depth of the bedrock and on the ice thickness and its inhomogeneities, i.e. internal layering of glaciers and subglacial lake exploration. In 1995 the INGV developed its own airborne radio echo sounding system, which is continuously being upgraded. During the 1995, 1997, 1999, 2001 and 2003 Italian AntarcticExpeditions, the RES system was used to investigate different Antarctic regions.During 2007-2008 campaign, new RES systems will be used. In the following the main characteristics of the systems will be briefly described. http://hdl.handle.net/2122/3890 Titolo: Glacio RADAR system and results<br/><br/>Autori: Zirizzotti, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Baskaradas, J. A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Bianchi, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Sciacca, U.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Tabacco, I. E.; Università di Milano/ Dipartimento scienza della terra, Via Cicognara 7 20129 Milano Italy; Zuccheretti, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia<br/><br/>Curatori: IEEE Aerospace and Electronics Systems Society, (AESS); IEEE Aerospace and Electronics Systems Society<br/><br/>Abstract: Since 1997 the Istituto Nazionale di Geofisica e Vulcanologia (INGV) in Italy has been involved in the development of the airborne RES system named Glacio RADAR, which is continuously upgraded. Radio Echo Sounding (RES) techniques are widely used in glaciological measurements. They are based on the use of radar systems, to obtain information concerning ice thickness of ice sheets and ice shelves, internal layering of glaciers, detection of inhomogeneities, exploration of subglacial lakes and identification of physical nature of subglacial interface. The Glacio RADAR is mounted on an aircraft and flies at an altitude around 300m above the ice surface during the survey. The first prototype operates in bistatic mode with separate transmit and receive one wire folded dipole installed beneath the aircraft wings. It works at 60 MHz with an envelope pulse width variable between 0.3 s and 1 s. The receiving window is 64 s which implies a maximum penetration depth (range) in the ice of about 5.3 km. The horizontal sampling rate is 10 traces/s at a mean aircraft speed of about 70 m/s. This would produce roughly 143 traces per kilometre (horizontal resolution of 1 trace every 7 m). The Navigation and geographical information is based on a on board GPS receiver giving longitude, latitude, altitude and time for the acquired radar trace. This radar was used in several Italian Antarctic Expeditions (1997, 1999, 2001 and 2003) and highlights of data results from these expeditions are presented here. http://hdl.handle.net/2122/3798 Titolo: A High Resolution Free Surface Model of the Mediterranean Sea<br/><br/>Autori: Tonani, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Pinardi, N.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Dobricic, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Pujol, I.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Fratianni, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia<br/><br/>Abstract: This study describes a new model implementationfor the Mediterranean Sea with what is currently the highestvertical resolution over the Mediterranean basin. The resolutionis of 1/16 ×1/16 in the horizontal and has 72 unevenlyspaced vertical levels. This model has been developed in theframe of the EU-MFSTEP project and is the operational forecastmodel currently used at the basin scale.The model considers an implicit free surface and this characteristicenhances the model’s capability to simulate the seasurface height variability and the net transport at the Strait ofGibraltar.In this study we show the calibration/validation experimentsperformed before and after the model was used forforecasting. The first experiment consists of a six-year simulationforced by a perpetual year forcing, and the other experimentis a simulation from January 1997 to December 2004,forcing the model with 6-h atmospheric forcing fields fromECMWF. The model Sea Level Anomaly has been comparedfor the first time with satellite SLA and with ARGO data toprovide evidence of the quality of the simulation.The results show that this model is capable of reproducingmost of the variability of the general circulation in theMediterranean Sea. However, some basic model inadequaciesstand out and should be corrected in the near future.