http://hdl.handle.net/2122/100 Sun, 26 May 2013 04:26:46 GMT 2013-05-26T04:26:46Z http://hdl.handle.net/2122/8712 Title: Scientific review on the Complex Eikonal, and research perspectives for the Ionospheric Ray-tracing and Absorption Authors: Settimi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Sciacca, U.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Bianchi, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: The present paper conducts a scientific review on the complex eikonal, extrapolating the research perspectives on the ionospheric ray-tracing and absorption. As regards the scientific review, the eikonal equation is expressed, and some complex-valued solutions are defined corresponding to complex rays and caustics. Moreover, the geometrical optics is compared to the beam tracing method, introducing the limit of the quasi-isotropic and paraxial complex optics approximations. Finally, the quasi-optical beam tracing is defined as the complex eikonal method applied to ray-tracing, discussing the beam propagation in a cold magnetized plasma. As regards the research perspectives, this paper proposes to address the following scientific problem: in absence of electromagnetic (e.m.) sources, consider a material medium which is time invariant, linear, optically isotropic, generally dispersive in frequency and inhomogeneous in space, with the additional condition that the refractive index is assumed varying even strongly in space. The paper continues the topics discussed by Bianchi et al. [2009], proposing a novelty with respect to the other referenced bibliography: indeed, the Joule’s effect is assumed non negligible, so the medium is dissipative, and its electrical conductivity is not identically zero. In mathematical terms, the refractive index belongs to the field of complex numbers. The dissipation plays a significant role, and even the eikonal function belongs to the complex numbers field. Under these conditions, for the first time to the best of our knowledge, suitable generalized complex eikonal and transport equations are derived, never discussed in literature. Moreover, in order to solve the ionospheric ray-tracing and absorption problems, we hint a perspective viewpoint. The complex eikonal equations are derived assuming the medium as optically isotropic. However, in agreement with the quasi isotropic approximation of geometrical optics, these equations can be referred to the Appleton-Hartree’s refractive index for an ionospheric magneto-plasma, which becomes only weakly anisotropic in the presence of Earth’s magnetic induction field. Finally, a simple formula is deduced for a simplified problem. Consider a flat layering ionospheric medium, so without any horizontal gradient. The paper proposes a new formula, useful to calculate the amplitude absorption due to the ionospheric D-layer, which can be approximately modelled by a linearized complex refractive index, because covering a short range of heights, between h1= 50 km and h2= 80 km about. Tue, 19 Mar 2013 23:00:00 GMT http://hdl.handle.net/2122/8712 2013-03-19T23:00:00Z http://hdl.handle.net/2122/8701 Title: Testing the IONORT-ISP system: A comparison between synthesized and measured oblique ionograms Authors: Settimi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Pietrella, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Bianchi, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Scotto, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Zuccheretti, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Makris, J.; Technological Educational Institute of Crete, P.O. Box 1939 Chania, Crete, Greece Abstract: The three-dimensional (3-D) electron density representation of the ionosphere computed by the assimilative IRI-SIRMUP-P (ISP) model was tested using IONORT (IONOspheric Ray-Tracing), a software application for calculating a 3-D ray-tracing for high frequency (HF) waves in the ionospheric medium. A radio link was established between Rome (41.8°N, 12.5°E) in Italy, and Chania (35.7°N, 24.0°E) in Greece, within the ISP validity area, and for which oblique soundings are conducted. The ionospheric reference stations, from which the autoscaled foF2 and M(3000)F2 data and real-time vertical electron density profiles were assimilated by the ISP model, were Rome (41.8°N, 12.5°E) and Gibilmanna (37.9°N, 14.0°E) in Italy, and Athens (38.0°N, 23.5°E) in Greece. IONORT was used, in conjunction with the ISP and the International Reference Ionosphere (IRI) 3-D electron density grids, to synthesize oblique ionograms. The comparison between synthesized and measured oblique ionograms, both in terms of the ionogram shape and the maximum usable frequency characterizing the radio path, demonstrates both that the ISP model can more accurately represent real conditions in the ionosphere than the IRI, and that the ray-tracing results computed by IONORT are reasonably reliable. Thu, 02 May 2013 22:00:00 GMT http://hdl.handle.net/2122/8701 2013-05-02T22:00:00Z http://hdl.handle.net/2122/8557 Title: Massive statistical analysis of autoscaled data: the case of the double reflection signature in mid-latitude vertical ionograms Authors: Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Scotto, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: This work shows how new capabilities can emerge from a massive statistical analysis of previously overlooked autoscaled data. In particular, the paper shows how autoscaling methods for vertical ionograms, specifically Autoscala, can offer a new kind of data that are not currently available at World Data Center or elsewhere and not reported by manual ionogram scalers. In this context, an example of such new analyses is the presentation of a statistics of occurrence of the double reflection phenomenon that sometimes characterizes ionograms. In order to establish this original statistics, a method developed to smooth out a specific autoscaling problem was utilized, and a large data set of ionograms recorded from 2003 to 2008 by the AIS-INGV ionosondes installed at the ionospheric stations of Rome (41.8°N, 12.5°E) and Gibilmanna (37.9°N, 14.0°E), Italy, was analyzed. The main results that emerged from the study are hence illustrated and briefly discussed. Mon, 31 Dec 2012 23:00:00 GMT http://hdl.handle.net/2122/8557 2012-12-31T23:00:00Z http://hdl.handle.net/2122/8519 Title: Power variation analysis of echo signals from ionospheric reflectors Authors: 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; Pietrella, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Sciacca, U.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Zuccheretti, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: A series of Power Virtual Height measurements (PVH) of radio echoes reflected from the ionosphere were acquired at a given frequency during the period 3–22 January 2008 with the purpose of studying the slow fading variations through time of the ionospheric channel. To obtain PVH data, an ionospheric vertical sounding system was suitably adapted to work at a single fixed frequency. PVH measurements were recorded between two routine ionospheric vertical soundings, providing a data type that enables evaluation of fading fluctuation through time. The time stability of the ionospheric layers is determined by analyzing the level of the received signal power within a chosen threshold. In this paper the fading behaviour and its characteristics are described, considering only temporal periodicity above 0.5 s. In a further analysis a relation is demonstrated between the recorded fading and the time stability of the signal within a fixed interval of values. Thu, 31 Jan 2013 23:00:00 GMT http://hdl.handle.net/2122/8519 2013-01-31T23:00:00Z http://hdl.handle.net/2122/8509 Title: Low-latitude equinoctial spread-F occurrence at different longitude sectors under low solar activity Authors: Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Zuccheretti, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Abadi, P.; Division of Ionosphere and Telecommunication, Space Science Center, Indonesian National Institute of Aeronautics and Space (LAPAN), Indonesia; A.J. de Abreu, A. J.; Universidade do Vale do Paraíba, São José dos Campos, Brazil; de Jesus, R.; Universidade do Vale do Paraíba, São José dos Campos, Brazil; Fagundes, P. R.; Universidade do Vale do Paraíba, São José dos Campos, Brazil; Supnithi, P.; Faculty of Engineering, King Mongkut’s Institute of Technology Ladkrabang (KMITL), Bangkok 10520, Thailand; Rungraengwajiake, S.; Faculty of Engineering, King Mongkut’s Institute of Technology Ladkrabang (KMITL), Bangkok 10520, Thailand; Nagatsuma, T.; Space Weather and Environment Informatics Laboratory, National Institute of Information and Communications Technology, Tokyo 184-8795, Japan; Tsugawa, T.; Space Weather and Environment Informatics Laboratory, National Institute of Information and Communications Technology, Tokyo 184-8795, Japan; Cabrera, M. A.; Laboratorio de Telecomunicaciones, DEEC, FACET, Universidad Nacional de Tucumán, Tucumán, Argentina; Ezquer, R. G.; Laboratorio de Ionósfera, Departamento de Física, FACET, Universidad Nacional de Tucumán, Tucumán, Argentina Abstract: We present the results of a comparative study of spread-F signatures over five low-latitude sites: Chiangmai (CGM; 18.8 N, 98.9 E, mag. Lat. 8.8 N), Thailand; Tanjungsari(TNJ; 6.9 S, 107.6 E, mag. Lat. 16.9 S), Indonesia; Palmas (PAL; 10.2 S, 311.8 E, mag. Lat. 0.9 S) and São José Dos Campos (SJC; 23.2 S, 314.1 E, mag. Lat. 14.0 S), Brazil; and Tucumán (TUC; 26.9 S, 294.6 E, mag. Lat. 16.8 S), Argentina. The investigation was based on simultaneous ionograms recorded by an FMCW (frequency modulated continuous-wave) at CGM, an IPS-71 (digital ionosonde from KEL aerospace) at TNJ, a CADI (Canadian Advanced Digital Ionosonde) at PAL and SJC, and an AIS-INGV (Advanced Ionospheric Sounder – Istituto Nazionale di Geofisica e Vulcanologia) at TUC, during the equinoctial periods March–April (R12 = 2.0 and R12 = 2.2) and September–October (R12 = 6.1 and R12 = 7.0) 2009, for very low solar activity. Spread-F signatures were categorized into two types: the range spread-F (RSF) and the frequency spread-F (FSF). The study confirms that the dynamics and the physical processes responsible for these phenomena are actually complicated. In fact, the features that arise from the investigation are different, depending on both the longitude sector and on the hemisphere. For instance, TUC, under the southern crest of the ionospheric equatorial ionization anomaly (EIA), shows a predominance of RSF signatures, while both SJC, under the southern crest of EIA but in a different longitude sector, and CGM, under the northern crest of EIA, show a predominance of FSF signatures. Moreover, the spread-F occurrence over the longitude sector that includes CGM and TNJ is significantly lower than the spread-F occurrence over the longitude sector of PAL, SJC, and TUC. Mon, 04 Feb 2013 23:00:00 GMT http://hdl.handle.net/2122/8509 2013-02-04T23:00:00Z http://hdl.handle.net/2122/8320 Title: IONORT: A Windows software tool to calculate the HF ray tracing in the ionosphere Authors: Settimi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Azzarone, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Bianchi, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Scotto, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Pietrella, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Editors: Monorchio, A.; Universita` di Pisa via Diotisalvi 2 -- 56126 PISA Abstract: This proceeding describes an applicative software tool, named IONORT (IONOspheric Ray Tracing), for calculating a three-dimensional ray tracing of high frequency waves in the ionospheric medium. This tool runs under Windows operating systems and its friendly graphical user interface facilitates both the numerical data input/output and the two/three-dimensional visualization of the ray path. In order to calculate the coordinates of the ray and the three components of the wave vector along the path as dependent variables, the core of the program solves a system of six first order differential equations, the group path being the independent variable of integration. IONORT uses a three-dimensional electron density specification of the ionosphere, as well as geomagnetic field and neutral particles-electrons collision frequency models having validity in the area of interest. Tue, 29 May 2012 22:00:00 GMT http://hdl.handle.net/2122/8320 2012-05-29T22:00:00Z http://hdl.handle.net/2122/8103 Title: The effect of collisions in ionogram inversion Authors: Scotto, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Settimi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: The results of this paper demonstrate that the effect of collisions on the group refraction index is small, when the ordinary ray is considered. If, however, in order to improve the performance of a system for automatic interpretation of ionograms, the information contained in ordinary and extraordinary traces is combined, the effect of collisions between the electrons and neutral molecules should be taken into account for the extraordinary ray. The magnitude of these differences is generally very small and must be compared with the resolution in the virtual vertical height of the ionosonde, resolution which is typically of the order of few kilometers. Mon, 31 Dec 2012 23:00:00 GMT http://hdl.handle.net/2122/8103 2012-12-31T23:00:00Z http://hdl.handle.net/2122/7933 Title: Atypical nighttime spread-F structure observed near the southern crest of the ionospheric equatorial ionization anomaly Authors: Fagundes, P. R.; Bittencourt, J. A.; Abreu, A. J.; Moor, L. P.; Muella, M. T. A. H.; Sahai, Y.; Abalde, J. R.; Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Sobral, J. H. A.; Abdu, M. A.; Pimenta, A. A.; Amorim, D. C. M. Abstract: An atypical nighttime spread-F structure is observed on ionograms at or above the F2 trace, near the crest of the ionospheric equatorial ionization anomaly (EIA) region. This ionospheric atypical spread-F phenomenon was observed using two closed spaced( 115 km) ionospheric soundings stations located in Sao Jose dos Campos (23.21 S, 45.97 W) and Cachoeira Paulista (22.70 S, 45.01 W), Brazil, in a low-latitude station (near the southern crest of the EIA region), during nighttime, low solar activity, and quiet geomagnetic conditions. This structure, in the initial phase, appears in the ionogram as a faint spread-F trace above or at the F2-layer peak height. After a few minutes, it develops into a strong spread-F trace, and afterwards, it moves to altitudes below the F2-layer peak heights. Finally, the atypical nighttime F-layer trace structure may remain for a while between the F-layer bottom side and peak height or can move to an altitude above the F-layer peak height, and then it disappears. In order to have a comprehensive view of the ionospheric environment characterizing the phenomenon under study, complementary data from six GPS station were used to investigate the ionosphere environment conditions, during both events. The six GPS stations used in this study are distributed from near the equatorial region to low latitudes and provide evidence that the atypical nighttime spread-F structures are not related with large scale equatorial irregularities (plasma bubbles). Fri, 06 Apr 2012 22:00:00 GMT http://hdl.handle.net/2122/7933 2012-04-06T22:00:00Z http://hdl.handle.net/2122/7916 Title: IONORT: a Windows software tool to calculate the HF ray tracing in the ionosphere Authors: Azzarone, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Bianchi, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Pietrella, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Scotto, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Settimi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: This paper describes an applicative software tool, named IONORT (IONOspheric Ray Tracing), for calculating a three-dimensional ray tracing of high frequency waves in the ionospheric medium. This tool runs under Windows operating systems and its friendly graphical user interface facilitates both the numerical data input/output and the two/three-dimensional visualization of the ray path. In order to calculate the coordinates of the ray and the three components of the wave vector along the path as dependent variables, the core of the program solves a system of six first order differential equations, the group path being the independent variable of integration. IONORT uses a three-dimensional electron density specification of the ionosphere, as well as geomagnetic field and neutral particles–electrons collision frequency models having validity in the area of interest. Mon, 30 Apr 2012 22:00:00 GMT http://hdl.handle.net/2122/7916 2012-04-30T22:00:00Z http://hdl.handle.net/2122/7711 Title: Estimating the vertical electron density profile from an ionogram: on the passage from true to virtual heights via the target function method Authors: Scotto, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Zolesi, B.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: The paper describes a new simple method of calculation by which an artificial ionogram trace is obtained from a given vertical electron density profile. The method is discussed in terms of the target function method used by Autoscala to output a reliable estimation of the real vertical electron density profile associated to the recorded ionogram. This new approach solves the issue of the pole in the calculation of virtual height, and consequently eliminates all the divergence phenomena that sometimes characterized the artificial ionogram traces computed by Autoscala. In contrast to the POLAN procedure, the technique introduced in this paper to pass from true to virtual heights is not based on any arithmetical operation related to changes of integration variables. Since the target function method on which Autoscala is based requires that the passage from a vertical electron density profile to an artificial ionogram be repeated a very large number of times, this new calculation procedure is advantageous in terms of speeding up the associated processing time. Fri, 27 Jan 2012 23:00:00 GMT http://hdl.handle.net/2122/7711 2012-01-27T23:00:00Z