Earth-prints

BFM-SI: A new implementation of the biogeochemical flux model in sea ice

Fri, 26 Feb 2010 22:58:59 GMT

Title: BFM-SI: A new implementation of the biogeochemical flux model in sea ice

Authors: Tedesco, Letizia; CMCC; Vichi, Marcello; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia

Abstract: This work describes a novel implementation of the Biogeochemical Flux Model (BFM) in a sea ice system (BFMSI). The chosen representative groups of the sea ice food web rely on the same dynamics as the BFM. The main differences between BFM and BFMSI stand in the type and number of functional groups, in the parameters assigned to several physiological and ecological processes and in the dimensional size classes they represent. The differential equations of BFMSI are written here according to the nomenclature associated to the new sea ice state variables. At the boundaries, the sea ice system is also coupled to the atmosphere and to the ocean through the exchange of organic and inorganic matter. This is done by computing the entrapment of particulate and dissolved matter and gases when sea ice grows and release to the ocean when sea ice melts to ensure mass conservation. The implementation of the BFM in sea ice and the coupling structure in General Circulation Models will add a new component that may provide new adequate estimate of the role and importance of sea ice biogeochemistry in the global carbon cycle.

EXPERIENCE IN MOBILE LASER SCANNING BY MEANS OF LYNX SYSTEM IN L’AQUILA CITY

Mon, 08 Mar 2010 22:58:59 GMT

Title: EXPERIENCE IN MOBILE LASER SCANNING BY MEANS OF LYNX SYSTEM IN L’AQUILA CITY

Authors: Pesci, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Loddo, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Casula, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Zampa, F.; SINECO SPA; Teza, G.; Università degli Studi di Padova (Dipartimento di Geoscienze)

Abstract: The terrestrial laser scanner is an efficient topographical instrumentation used to acquire a redundant number of points distributed over a physical surface. The goal of laser scanning is the definition of very accurate models of the studied areas. In this way, deformations or changes can be monitored by means of repeated surveys in different epochs [Pesci et al., 2005; 2007]. The laser signal is characterized by highly collimated, monochromatic, and coherent radiation that is well suitable for very short impulse generation in the nanosecond scale. The operating methodology of a time-of-flight laser scanner is similar to a laser range-finder, measuring the time it takes a laser pulse to travel from a transmitter to the surface surveyed, and back to a detector device. The range d is computed using the relation d = ct / 2, where t is the time of flight and c is the speed of light. The advantage of this instruments is the laser beam deflection over a very accurate angular grid, that can be obtained by oscillating and rotating mirrors, thus providing a wide coverage area between adjacent points. Each point is collected into a local reference system consisting of the origin at the instrument sensor, well-known angular parameters, and very accurate measurements of range. Together with point coordinates (x, y, z) , radiometric values related to the surveyed object’s reflectivity can be calculated from returned signal energy. The maximum measurable range depends on the illuminated material roughness and color, and the laser wavelength [Fidera et al. 2004, Pesci and Teza, 2008]. Divergence values for new generation long-range scanners are extremely reduced, illuminating very small surface elements for each shot. The spot dimension increases linearly with the distance, and is always greater than the lower limit of the instantaneous field of view (IFOV) due to physical diffraction. Effective laser scanner characteristics are defined by a set of parameters, including: range resolution (depending on telemeter efficiency), single point measurement accuracy (depending on the internal electronic device, signal-to-noise ratio and critical time needed for pulse recognition), beam divergence (which defines the IFOV, depending on laser wavelength), and minimum angular step (depending on the internal mirrors calibrated system) [Wehr and Lohr 1999]. Overlap is the laser scanning strategy that can reduce errors, because redundant points are acquired belonging to the same illuminated area. A common overlap is obtained by fixing the ratio between spot dimension (the area illuminated by a single pulse with a given divergence) and angular step so that a given point is measured 10 times. For instance, if the divergence is 3 mrad and angular variation about 0.3 mrad, at 100 m distance, an element included in a 3 cm area is observed 10 times. The final result of a laser scanner application is a very dense point cloud, with radiometric reflectivity data for each point.

Carta della vulnerabilità dell'acquifero salentino: area campione a sud di Lecce

Fri, 29 Oct 1999 22:58:59 GMT

Title: Carta della vulnerabilità dell'acquifero salentino: area campione a sud di Lecce

Authors: Cotecchia, V.; Politecnico di Bari; Daurù, M.; Politecnico di Bari; Limoni, P. P.; CNR-IRPI; Mitolo, D.; CNR-IRPI; Polemio, M.; CNR-IRPI

Abstract: L'area di studio è rappresentativa sia degli aspetti idrogeologici tipici delle zone di alimentazione del Salento sia degli effetti dell'antropizzazione, è sede di nurnerosi pozzi adibiti ad uso potabile. Lo studio è stato finalizzato alla redazione della carta della vulnerabilità dell’acquifero con ii metodo SINTACS. La natura sperimentale dell’applicazione è legata alle peculiarità dell’acquifero salentino e all’assenza di esperienze pregresse per tale contesto. Sono stati effettuati rilievi diretti, prove idrogeologiche e piü cicli di campionarnento idrico ed analisi di laboratorio. I centri di pericolo sono stati censiti sulla base delle banche dati disponibili ed ispezionando ii territorio. L’infiltrazione si è dirnostrata molto rapida, anche laddove l’acquifero non affiora. La vulnerabilità è risultata notevole, da alta a molto elevata. La qualita delle acque, per quanto tuttora buona, si è dimostrata sensibile alla posizione e all’azione dei centri di pericolo. I rischi di degrado qualitativo sono risultati non trascurabili.

Velocity and attenuation tomography of the Umbria Marche 1997 fault system: Evidence of a fluid-governed seismic sequence

Wed, 14 Oct 2009 22:58:59 GMT

Title: Velocity and attenuation tomography of the Umbria Marche 1997 fault system: Evidence of a fluid-governed seismic sequence

Authors: Chiarabba, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; De Gori, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Piccinini, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia

Abstract: The 1997 Umbria Marche is probably the best ever monitored normal faulting seismic sequence. Seismicity migration and multiple main shocks characterize the activation of a 40-km-long system of contiguous fault segments, as documented by seismological data. Many authors as indicative of fault weakening by fluids migration have interpreted this behaviour. In this study, we create a new catalogue of high quality P- and S-wave arrival times merging data recorded by permanent and temporary stations to improve the resolution of velocity and attenuation models and earthquake locations. We show that the relocated earthquakes and the joint interpretation of P- and S-wave velocity and attenuation models help in understanding the faulting processes, revealing new details of the geometry of the main faults and physical state of fluids within the crustal volume. We observe that large aftershocks occur on the top and within the Triassic evaporitic layer, a rock volume locally characterised by fluid over-pressured, as evidenced by high VP/VS and low QP/QS anomalies. Velocity and attenuation heterogeneities are evidence that the migration of fluid pressure along the fault system is the driving mechanism of the prolonged earthquake sequence.