[1] A new model for scintillation on transionospheric links, based on a hybrid method and valid for strong scintillations, has been developed and used to construct a software transionospheric channel simulator. The method is a combination of the complex phase method and the random screen technique. The parameters of the random screen are determined as the result of a rigorous solution to the problem of propagation inside the ionosphere using the extended Rytov approximation (the complex phase method). The random two-dimensional spatial spectrum at the screen is then transferred down to the Earth's surface employing the rigorous relationships of the random screen theory. Thus the complex phase method can adequately introduce a random screen below the ionosphere for L-band frequencies. The technique is capable of producing statistical characteristics and simulating time realizations of the field for a wide range of input parameters. Preliminary results are presented for both weak and strong scintillations.

Although formulae are available to determine tracking jitter (variance of the phase tracking error at the output of the Global Navigation Satellite Systems receiver phase‐locked loop) resulting from scintillation for GPS/SBAS C/A code processing and semicodeless GPS L1 and L2 Y‐code, these require input of the spectral parameters p (inverse power law of the phase power spectral density (PSD)) and T (spectral strength of the phase PSD at 1 Hz) which will not generally be available. It would certainly be more convenient if tracking jitter could be determined just from scintillation indices (S4 and σϕ) enabling determination when spectral parameters are not readily available and permitting tracking jitter for all the simultaneously observed satellites to be easily determined and used in a scintillation mitigation scheme. The main difficulty is that the Fresnel frequency, fF, which is an important feature of the amplitude PSD, should be known. Here a method is proposed which uses both scintillation indices (σϕ and S4) to give an additional relation to find both p and T. This makes use of the known general fading frequency behavior of the PSD spectrum which is different between amplitude and phase scintillation. This difference is exploited, utilizing approximate models of the PSD for both amplitude and phase, to define equations that can be solved for p and T for any given fF. Even when fF is not known, it is shown that by taking account of the range of physically realistic values of fF, the tracking jitter can generally be determined to a reasonable degree of accuracy.

[1] This paper addresses the effects of scintillation on high-latitude paths of propagation. To specify the high-latitude ionosphere environment as a time-dependent threedimensional distribution of the electron density, the first-principles ionospheric model UAF EPPIM (University of Alaska Fairbanks Eulerian Parallel Polar Ionosphere Model) is utilized. For the specification of time-varying small-scale irregularities, superimposed onto the background EPPIM, the full three-dimensional inverse power law spectrum is chosen. It is augmented with the introduction of the irregularities' aspect ratio for two mutually perpendicular directions: transverse (to the geomagnetic field) direction and for the longitudinal direction to the transverse one. This full description of the propagation environment, comprised of the ''background'' and ''irregularities'' components, is further merged with the propagation scintillation model to set up the computational suite, capable of modeling the scintillation effects. The parameters of the spectrum of the electron density fluctuations, as well as the models of meso-scale local polar structures (e.g., patches) are chosen empirically. The integrated simulator enables realistic predictions of the scintillation effects for high-latitude transionospheric propagation for a number of different propagation scenarios for GPS L-band and other UHF transionospheric signals. The specific scintillation effects, caused by ionospheric patches, are simulated.Citation: Maurits, S. A., V. E. Gherm, N. N. Zernov, and H. J. Strangeways (2008), Modeling of scintillation effects on highlatitude transionospheric paths using ionospheric model (UAF EPPIM) for background electron density specifications, Radio Sci., 43, RS4001,

[1] A wideband HF simulator has been constructed on the basis of a detailed physical model of propagation which can generate a time realization of the HF wideband channel for any HF carrier frequency, bandwidth, transmitter receiver path and background, and stochastic (irregularity) ionosphere models. To accomplish this, a comprehensive solution has been obtained on the basis of the complex phase method (Rytov's method) to the problem of HF wave propagation for the most general case of a three-dimensional (3-D) inhomogeneous ionosphere with time-varying electron density fluctuations. A simulation is presented for a 1000 km path for which E and low-and high-angle F mode paths exist. The time-varying field owing to each of these paths is summed at the receiving location, enabling the calculation of the scattering function and also the time realization of the received signal shown as a function of both fast and slow time.Citation: Gherm, V. E., N. N. Zernov, and H. J. Strangeways (2005), HF propagation in a wideband ionospheric fluctuating reflection channel: Physically based software simulator of the channel, Radio Sci., 40, RS1001,

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Abstract. The complex phase method has been further extended to the problem of electromagnetic (EM) field scintillations on Earth-satellite GPS paths of propagation. The numerical and analytic technique based on the method has been developed to characterize the transionospheric channel of propagation. The effects of additional range errors due to the ionospheric electron density fluctuations in space and time have been studied taking into account the ray bending due to the inhomogeneous background ionosphere and the diffraction on local random ionospheric inhomogeneities. In the method developed, the impact of the Earth's magnetic field is accounted for by the anisotropic spatial spectrum of the ionospheric turbulence with different outer scales along and across the magnetic field lines. The variances of the EM field phase (yielding range errors) and level (log amplitude) fluctuations have been calculated for different models of the background ionospheres characterized by different height electron density profiles and total electron content. The conditions of the saturated regime of propagation, which will likely result in the degradation of a GPS navigation system, have been discussed. In addition, the scattering function of the GPS transionospheric channel of propagation has been constructed and simulated for a wideband signal.

[1] A previously developed scintillation propagation model for L band signals on transionospheric paths has been further extended to describe the effects caused by the localized structure of plasma bubbles in the low-latitude ionosphere. This takes into account quasi-deterministic and random structures typical of bubbles. The model can produce signal statistical moments (power spectra, correlation functions, scintillation index, etc.) and generate random time series including the case of through bubble propagation. The simulated random time series of the field demonstrate the characteristic nonstationary behavior caused by the presence and motion of the bubble structures through the path of propagation, showing that strong enhancements of the scintillation index (S 4 ) can occur depending on the parameters of the bubble and the path. Modeling results are compared with scintillation records due to bubbles passing through GPS signal paths to a receiver at Douala, Cameroon. This shows good agreement providing validation for the bubble and propagation model.

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