Alessandro Settimi

IONORT: A Windows software tool to calculate the HF ray tracing in the ionosphere

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.

A method to test HF ray tracing algorithm in the ionosphere by means of the virtual time delay

As well known a 3D ray tracing algorithm furnishes the rays coordinates, the three components of the wave vector and the group time delay of the wave along the path. This last quantity can be compared with the measured group delay to check the performance of the algorithm. Simulating a perfect reflector at an altitude equal to the virtual height of reflection the virtual delay is assumed as a real group delay. For a monotonic electronic density profile we find a very small relative difference between the calculated and the simulated delay both for analytic and discrete 3D electronic density models.

Scientific Review on the Ionospheric Absorption and Research Prospects of a Complex Eikonal Model for One-Layer Ionosphere

The present paper conducts a scientific review on ionospheric absorption, extrapolating the research prospects of a complex eikonal model for one-layer ionosphere. As regards the scientific review, here a quasi-longitudinal (QL) approximation for nondeviative absorption is deduced which is more refined than the corresponding equation reported by Davies (1990). As regards the research prospects, a complex eikonal model for one-layer ionosphere is analyzed in depth here, already discussed by Settimi et al. (2013). A simple formula is deduced for a simplified problem. A flat, layered ionospheric medium is considered, without any horizontal gradient. The authors prove that the QL nondeviative amplitude absorption according to the complex eikonal model is more accurate than Rawer’s theory (1976) in the range of middle critical frequencies.

The effect of collisions in ionogram inversion

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.

Assessment of Electromagnetic Absorption of Ice From Ice Core Measurements

Ice core drillings have been performed in various zones in Antarctica and Greenland to obtain climatological information, study ice properties, or analyze air and dust encapsulated in the ice during the quaternary period. During these procedures, a set of measurements to characterize the ice and to evaluate its physical and chemical properties are usually performed in situ. In particular, using known temperature and dielectric profiles (DEP measurements), it is possible to evaluate the ice electromagnetic power absorption profile, valid at the drilling site. In the last decades, bedrock characterization through radio echo sounding surveys has been improved by the analysis of the power of radar echoes. This way, analysis of the electromagnetic properties of bedrock interfaces makes it possible to assess the physical characteristics and to distinguish between wet and dry conditions. Power variation of the received echoes also depends on ice absorption and on bedrock reflectivity due to specific physical conditions of the ice. In this paper, the propagation of electromagnetic waves through the ice sheet is examined, and in particular, a new method for establishing the electromagnetic absorption profile for ice from core drilling measurements is proposed and discussed. Variation in the ice absorption is deduced, starting from the analysis of ice core data from the European Project for Ice Coring in Antarctica (EPICA) at the Concordia station (Antarctica) and from the Greenland Ice Core Project (GRIP) site (Greenland). This direct method of measurement is proposed with the aim of defining common characteristics of the ice absorption rate that are valid both in Antarctica and in Greenland.

Real time 3D ionospheric modelling with ray tracing application over Mediterranean area

This paper reviews the concept and some practical examples of instantaneous 3D modelling of regional ionosphere, based on ionosonde data from the INGV continuously operating stations at Roma and Gibilmanna. The 3D model was built considering characteristic anchor points for each of the different ionospheric regions and joining these points by an adaptive ionospheric profiler derived from the one used in Autoscala. The model produces as an output a 3D matrix which can be profitably used as an input for a Matlab/Fortran based ray tracing program recently developed at INGV. This paper deals about some practical examples of instantaneous 3D modelling of regional ionosphere, based on ionosonde data from the Istituto Nazionale di Geofisica e Vulcanologia, INGV. Characteristic anchor points have been chosen for each ionospheric regions. These points are joint by an adaptive ionospheric profiler derived from the one used in Autoscala. For the F2 region the anchor point is given by the real height hmF2 of the layer and its critical frequency foF2. These values are obtained basing on the observed heights (hmF2ROMA[OBS] and hmF2GIBILMANNA[OBS]) and critical frequencies (foF2ROMA[OBS] and foF2GIBILMANNA[OBS]) of the F2 layer, which are compared with the corresponding monthly median given by CCIR maps using Shimazakis formulation. The differences δhmF2ROMA = hmF2ROMA[OBS]-hmF2ROMA[CCIR] and δhmF2GIBILMANNA = hmF2 GIBILMANNA [OBS]-hmF2 GIBILMANNA [CCIR] are thus computed and used in Kriging method to update the values given by CCIR maps. For the F1 region the critical frequency is derived form a solar zenith angle dependent model adjusted to match the values of foF1 measured in Roma and Gibilmanna. For the E region the height is set to 110 km, while the critical frequency is estimated by a standard solar zenith angle and dependent model. The model provides as an output a regional estimation of the electron density over the Mediterranean area in form of a 3D matrix. Such a matrix can be profitably used as an input for a 3D ray tracing program used at INGV. In order to test the performance of 3D model represented as output (matrix in figure 1) a 3D ray tracing in some special cases.