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  • spherical cap harmonics  (3)
  • 04. Solid Earth::04.02. Exploration geophysics::04.02.07. Instruments and techniques  (2)
  • 2005-2009  (5)
  • 1
    Publication Date: 2020-11-20
    Description: The importance of detecting possible electromagnetic signatures due to big earthquakes is self-evident, signatures which can be either anticipating, simultaneous or subsequent with respect to the main shock. Taking advantage of the present low Earth orbiting CHAMP satellite, we apply two “ad hoc” techniques both based on the Information Theory (after the seminal monograph by Shannon [1]) to the satellite magnetic data with the aim at extracting eventual time anomalies. These techniques have different time-space resolutions: the first technique requires a preliminary spherical harmonic analysis of daily magnetic data and, potentially, detects long-wavelength variations, while the second uses a preliminary wavelet analysis and can detect shorter-wavelength anomalies. Some examples are given for magnetic satellite data taken in correspondence with the two big earthquakes occurred in the Sumatra region on 26 December 2004 (M = 9.1) and 28 March 2005 (M = 8.6).
    Description: Published
    Description: Cambridge, UK, February 24-26, 2009
    Description: 1.6. Osservazioni di geomagnetismo
    Description: 2.6. TTC - Laboratorio di gravimetria, magnetismo ed elettromagnetismo in aree attive
    Description: open
    Keywords: Earthquake precursors ; Magnetic field ; Satellite data ; Wavelet Analysis ; Shannon Entropy ; 04. Solid Earth::04.02. Exploration geophysics::04.02.07. Instruments and techniques ; 05. General::05.05. Mathematical geophysics::05.05.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Conference paper
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  • 2
    Publication Date: 2017-04-03
    Description: The "global" representation of the geomagnetic field in terms of ordinary spherical harmonics (SHs) and its corresponding set {g,h} of coefficients has been studied extensively, but the "local" representation in terms of spherical cap harmonics (SCHs) and its corresponding set {G,H} of coefficients is not yet well understood. This paper clarifies some of the main properties of the SCHs and their proper use along with their relationship with the SHs. In particular, it shows that for the spherical cap part of a global field specified by spherical harmonics there is a strict relation between the ordinary Legendre functions of the global representation and the fractional functions of the local expansion; hence we can express the set of coefficients {G,H} in terms of the set {g,h}. Finally, some attention will be given to the role of the leading (n=0, m=0) term of the SCH expansion.
    Description: Published
    Description: 935-941
    Description: JCR Journal
    Description: reserved
    Keywords: spherical cap harmonics ; spherical harmonics ; geomagnetic field modelling ; 04. Solid Earth::04.05. Geomagnetism::04.05.03. Global and regional models ; 05. General::05.05. Mathematical geophysics::05.05.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
    Publication Date: 2019-11-04
    Description: Models of the geomagnetic field are mathematical expressions able to represent the Earth's magnetic field space and time variations. Time variations on the long term basis are represented by the so-called secular variation. This paper describes and reviews recent activities of the Italian group at the Istituto Nazionale di Geofisica in regional magnetic field modelling. The models are introduced starting from the classical technique of Spherical Harmonic Analysis (SHA) undertaken for the first time by Gauss, the polynomial analysis and the regional harmonic analysis, specifically introduced as a regional analogue of SHA. In this last group the recent techniques of Spherical Cap Harmonic Analysis (SCHA), Translated Origin Spherical Cap Analysis (TOSCA) and Adjusted Spherical Cap Harmonic Analysis (ASHA) are also described and discussed.
    Description: JCR Journal
    Description: open
    Keywords: regional modelling ; spherical cap harmonics ; geomagnetic field ; 04. Solid Earth::04.05. Geomagnetism::04.05.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 2784464 bytes
    Format: application/pdf
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  • 4
    Publication Date: 2020-05-29
    Description: Exploration of ocean seafloor is of paramount importance for a better understanding of the geodynamic evolution of our Planet. The pilot experiment of ORION-GEOSTAR 3 EC project was the first long-term continuous geophysical and oceanographic experiment of an important seafloor area of Southern Tyrrhenian Sea, the Marsili abyssal plain. The latter hosts the Marsili Seamount which is Europe’s one of the largest underwater volcano of Plio-Pleistocenic age. In spite of its dimensions, it is rather unknown about the present characteristics and activity. For this reason, we deployed a deep-sea observatory network, composed by two bottom observatories, on the seafloor at the base of the seamount at 3320 m b.s.l., in the period December 2003-May 2005. Some of the instruments on board the observatory were: broad-band seismometers, hydrophones, gravity meter, two magnetometers (scalar and vectorial), 3D single-point current meter, ADCP, CTD, automatic pH analyser and off-line water sampler for laboratory analyses. The first successful scientific objective was to obtain long-term continuous recordings under a unique time reference. The data analysis shows that they are generally of good quality and really continuous (only a few gaps). As a first step we performed a classification of seismic waveforms, a first inversion of magnetic variational data, and a first analysis of gravity meter, chemical and oceanographic data. Analysis of individual time series has shown interesting results, i.e. depth of the magnetic Moho under the Marsili, attenuation of recorded seismic body waves and clues of hydrothermal circulation. We show examples of the preliminary data analysis together with first results and comparisons among data coming from different sensors.
    Description: Published
    Description: Cambridge, UK, February 24-26, 2009
    Description: 1.8. Osservazioni di geofisica ambientale
    Description: 3.8. Geofisica per l'ambiente
    Description: open
    Keywords: Marsili Basin and Volcanic Seamount ; Exploration with seafloor observatories ; ORION-GEOSTAR 3 EC project ; 03. Hydrosphere::03.01. General::03.01.01. Analytical and numerical modeling ; 04. Solid Earth::04.02. Exploration geophysics::04.02.07. Instruments and techniques
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Conference paper
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  • 5
    Publication Date: 2019-11-04
    Description: The properties of the Earth's core magnetic field and its secular variation are poorly known for the Antarctic. The increasing availability of magnetic observations from airborne and satellite surveys, as well as the existence of several magnetic observatories and repeat stations in this region, offer the promise of greatly improving our understanding of the Antarctic core field. We investigate the possible development of a Laplacian reference model of the core field from these observations using spherical cap harmonic analysis. Possible uses and advantages of this approach relative to the implementations of the standard global reference field are also considered.
    Description: JCR Journal
    Description: open
    Keywords: Geomagnetic reference field ; spherical cap harmonics ; polar regions ; 04. Solid Earth::04.05. Geomagnetism::04.05.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 1918730 bytes
    Format: application/pdf
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