Electron density irregularities in the F region excited by the European incoherent scatter (EISCA... more Electron density irregularities in the F region excited by the European incoherent scatter (EISCAT) high-power high-frequency (HF) facility in Ramfjordmoen, Norway, have been studied in detail by observing scintillations of 250-MHz satellite signals traversing the HF beam. Spaced antenna measurements were performed to determine the temporal structure of scintillation and the drift of the irregularities. Studies of scintillation spectra indicate
Eight spaced antennas were used to receive 250-MHz signals from quasi-geostationary polar beacon ... more Eight spaced antennas were used to receive 250-MHz signals from quasi-geostationary polar beacon satellites. The system was deployed in such a way as to intercept the ionospheric volume illuminated by the European incoherent scatter (EISCAT) high-power HF heating facility near Tromsø, Norway (69.6°N, 19.2°E). The spaced-receiver analysis was then used to investigate the relationship between the elongation, the characteristic velocity,
... forecast systems based on real-time measurements may explore the facts that the irregularitie... more ... forecast systems based on real-time measurements may explore the facts that the irregularities are field ... which will be able to forecast the onset of plasma instabilities and their evolution (plasma bubbles). ... Due to its orbital period, the satellite will be able to track the evolution and ...
During its transit through a region of equatorial ionospheric irregularities, sensors on board th... more During its transit through a region of equatorial ionospheric irregularities, sensors on board the Communication/Navigation Outage Forecasting System (C/NOFS) satellite provide a one-dimensional description of the medium, which can be extended to two dimensions if the structures are assumed to be elongated in the direction of the magnetic field lines. The C/NOFS scintillation calculation approach assumes that the medium is equivalent to a diffracting screen with random phase fluctuations that are proportional to the irregularities in the total electron content, specified through the product of the directly measured electron density by an estimated extent of the irregularity layer along the raypaths. Within the international collaborative effort anticipated by the C/NOFS Science Definition Team, the present work takes the vertical structure of the irregularities into more detailed consideration, which could lead to improved predictions of scintillation. Initially, it describes a flexible model for the power spectral density of the equatorial ionospheric irregularities, estimates its shape parameters from C/NOFS in situ data and uses the signal-to-noise ratio S/N measurements by the São Luís coherent scatter radar to estimate the mean square electron density fluctuation <ΔN2> within the corresponding sampled volume. Next, it presents an algorithm for the wave propagation through a three-dimensional irregularity layer which considers the variations of <ΔN2> along the propagation paths according to observations by the radar. Data corresponding to several range-time-intensity maps from the radar is used to predict time variations of the scintillation index S4 at the L1 Global Positioning System (GPS) frequency (1575.42 MHz). The results from the scintillation calculations are compared with corresponding measurements by the colocated São Luís GPS scintillation monitor for an assessment of the prediction capability of the present formulation.
Data from the Planar Langmuir Probe onboard Communication/ Navigation Outage Forecasting System w... more Data from the Planar Langmuir Probe onboard Communication/ Navigation Outage Forecasting System will be combined with coherent scatter radar and scintillation measurements to analyze the performance of different propagation models of satellite signals. This work will characterize: (i) the prediction capability of a purely space-based phase-screen scintillation model in comparison with another that represents the variation of the irregularity strength along ray paths in detail; and (ii) how early in time it is possible to detect irregularity structures, estimate their temporal and spatial evolution and predict their effects on propagation through different ionospheric regions at later instants of time.
IEEE Transactions on Antennas and Propagation, 2012
The effects from lateral variations of irregular terrain on the propagation of radio waves are co... more The effects from lateral variations of irregular terrain on the propagation of radio waves are considered by the representation of the vector fields in terms of two scalar Hertz potentials in spherical coordinates. The combination of three-dimensional parabolic equations for these potentials with an impedance boundary condition for the ground, followed by a transformation of variables, will define a boundary-condition problem characterized by equations displaying coefficients that depend on the terrain height function and its partial derivatives. The problem solution through the Crank-Nicolson scheme will lead to a sparse system of linear equations, which will be solved by a direct method. The resulting numerical model will be applied to test cases to show similar features to those from examples described in the literature, taken as references for validation purposes.
Many models have been proposed to represent diffraction effects on the propagation of radio waves... more Many models have been proposed to represent diffraction effects on the propagation of radio waves over irregular terrain in the VHF and UHF bands. Predictions from these models have been compared with results from associated field-strength measurements available in extensive databases that also incorporate the technical parameters of thousands of VHF and UHF links. Some possible sources of the still high values of the standard deviations of errors between predictions and measurements will be identified and discussed, with particular attention to uncertainties on digital elevation models and on the effective Earth's radius, as well as to effects from lateral propagation.
Thousands of path profiles incorporated into the ITU-R Study Group 3 (DBSG5) database and those e... more Thousands of path profiles incorporated into the ITU-R Study Group 3 (DBSG5) database and those estimated from the shuttle radar topography mission (SRTM) digital elevation model for the same terminal coordinates will be compared. Models that estimate diffraction effects on the propagation of radio waves over irregular terrain in the VHF and UHF bands available for digital TV applications will be used to predict field strengths that will be compared with those from the corresponding measurements. The mean value and the standard deviation of the difference between measurements and predictions will be presented for each model and for both the DBSG5 and the SRTM terrain profiles, as functions of their number of main obstacles. A better basis for comparison between predictions and experimental data was obtained from a special measurement series performed by HTI to determine the height function of the received field strength. These measurements will be described, also compared with model predictions and statistically analyzed.
IEEE Transactions on Antennas and Propagation, 2012
The effects from lateral variations of irregular terrain on the propagation of radio waves are co... more The effects from lateral variations of irregular terrain on the propagation of radio waves are considered by the representation of the vector fields in terms of two scalar Hertz potentials in spherical coordinates. The combination of three-dimensional parabolic equations for these potentials with an impedance boundary condition for the ground, followed by a transformation of variables, will define a boundary-condition problem characterized by equations displaying coefficients that depend on the terrain height function and its partial derivatives. The problem solution through the Crank-Nicolson scheme will lead to a sparse system of linear equations, which will be solved by a direct method. The resulting numerical model will be applied to test cases to show similar features to those from examples described in the literature, taken as references for validation purposes.
Many models have been proposed to represent diffraction effects on the propagation of radio waves... more Many models have been proposed to represent diffraction effects on the propagation of radio waves over irregular terrain in the VHF and UHF bands. Predictions from these models have been compared with results from associated field-strength measurements available in extensive databases that also incorporate the technical parameters of thousands of VHF and UHF links. Some possible sources of the still high values of the standard deviations of errors between predictions and measurements will be identified and discussed, with particular attention to uncertainties on digital elevation models and on the effective Earth's radius, as well as to effects from lateral propagation.
Thousands of path profiles incorporated into the ITU-R Study Group 3 (DBSG5) database and those e... more Thousands of path profiles incorporated into the ITU-R Study Group 3 (DBSG5) database and those estimated from the shuttle radar topography mission (SRTM) digital elevation model for the same terminal coordinates will be compared. Models that estimate diffraction effects on the propagation of radio waves over irregular terrain in the VHF and UHF bands available for digital TV applications will be used to predict field strengths that will be compared with those from the corresponding measurements. The mean value and the standard deviation of the difference between measurements and predictions will be presented for each model and for both the DBSG5 and the SRTM terrain profiles, as functions of their number of main obstacles. A better basis for comparison between predictions and experimental data was obtained from a special measurement series performed by HTI to determine the height function of the received field strength. These measurements will be described, also compared with model predictions and statistically analyzed.
Electron density irregularities in the F region excited by the European incoherent scatter (EISCA... more Electron density irregularities in the F region excited by the European incoherent scatter (EISCAT) high-power high-frequency (HF) facility in Ramfjordmoen, Norway, have been studied in detail by observing scintillations of 250-MHz satellite signals traversing the HF beam. Spaced antenna measurements were performed to determine the temporal structure of scintillation and the drift of the irregularities. Studies of scintillation spectra indicate
Eight spaced antennas were used to receive 250-MHz signals from quasi-geostationary polar beacon ... more Eight spaced antennas were used to receive 250-MHz signals from quasi-geostationary polar beacon satellites. The system was deployed in such a way as to intercept the ionospheric volume illuminated by the European incoherent scatter (EISCAT) high-power HF heating facility near Tromsø, Norway (69.6°N, 19.2°E). The spaced-receiver analysis was then used to investigate the relationship between the elongation, the characteristic velocity,
... forecast systems based on real-time measurements may explore the facts that the irregularitie... more ... forecast systems based on real-time measurements may explore the facts that the irregularities are field ... which will be able to forecast the onset of plasma instabilities and their evolution (plasma bubbles). ... Due to its orbital period, the satellite will be able to track the evolution and ...
During its transit through a region of equatorial ionospheric irregularities, sensors on board th... more During its transit through a region of equatorial ionospheric irregularities, sensors on board the Communication/Navigation Outage Forecasting System (C/NOFS) satellite provide a one-dimensional description of the medium, which can be extended to two dimensions if the structures are assumed to be elongated in the direction of the magnetic field lines. The C/NOFS scintillation calculation approach assumes that the medium is equivalent to a diffracting screen with random phase fluctuations that are proportional to the irregularities in the total electron content, specified through the product of the directly measured electron density by an estimated extent of the irregularity layer along the raypaths. Within the international collaborative effort anticipated by the C/NOFS Science Definition Team, the present work takes the vertical structure of the irregularities into more detailed consideration, which could lead to improved predictions of scintillation. Initially, it describes a flexible model for the power spectral density of the equatorial ionospheric irregularities, estimates its shape parameters from C/NOFS in situ data and uses the signal-to-noise ratio S/N measurements by the São Luís coherent scatter radar to estimate the mean square electron density fluctuation <ΔN2> within the corresponding sampled volume. Next, it presents an algorithm for the wave propagation through a three-dimensional irregularity layer which considers the variations of <ΔN2> along the propagation paths according to observations by the radar. Data corresponding to several range-time-intensity maps from the radar is used to predict time variations of the scintillation index S4 at the L1 Global Positioning System (GPS) frequency (1575.42 MHz). The results from the scintillation calculations are compared with corresponding measurements by the colocated São Luís GPS scintillation monitor for an assessment of the prediction capability of the present formulation.
Data from the Planar Langmuir Probe onboard Communication/ Navigation Outage Forecasting System w... more Data from the Planar Langmuir Probe onboard Communication/ Navigation Outage Forecasting System will be combined with coherent scatter radar and scintillation measurements to analyze the performance of different propagation models of satellite signals. This work will characterize: (i) the prediction capability of a purely space-based phase-screen scintillation model in comparison with another that represents the variation of the irregularity strength along ray paths in detail; and (ii) how early in time it is possible to detect irregularity structures, estimate their temporal and spatial evolution and predict their effects on propagation through different ionospheric regions at later instants of time.
IEEE Transactions on Antennas and Propagation, 2012
The effects from lateral variations of irregular terrain on the propagation of radio waves are co... more The effects from lateral variations of irregular terrain on the propagation of radio waves are considered by the representation of the vector fields in terms of two scalar Hertz potentials in spherical coordinates. The combination of three-dimensional parabolic equations for these potentials with an impedance boundary condition for the ground, followed by a transformation of variables, will define a boundary-condition problem characterized by equations displaying coefficients that depend on the terrain height function and its partial derivatives. The problem solution through the Crank-Nicolson scheme will lead to a sparse system of linear equations, which will be solved by a direct method. The resulting numerical model will be applied to test cases to show similar features to those from examples described in the literature, taken as references for validation purposes.
Many models have been proposed to represent diffraction effects on the propagation of radio waves... more Many models have been proposed to represent diffraction effects on the propagation of radio waves over irregular terrain in the VHF and UHF bands. Predictions from these models have been compared with results from associated field-strength measurements available in extensive databases that also incorporate the technical parameters of thousands of VHF and UHF links. Some possible sources of the still high values of the standard deviations of errors between predictions and measurements will be identified and discussed, with particular attention to uncertainties on digital elevation models and on the effective Earth's radius, as well as to effects from lateral propagation.
Thousands of path profiles incorporated into the ITU-R Study Group 3 (DBSG5) database and those e... more Thousands of path profiles incorporated into the ITU-R Study Group 3 (DBSG5) database and those estimated from the shuttle radar topography mission (SRTM) digital elevation model for the same terminal coordinates will be compared. Models that estimate diffraction effects on the propagation of radio waves over irregular terrain in the VHF and UHF bands available for digital TV applications will be used to predict field strengths that will be compared with those from the corresponding measurements. The mean value and the standard deviation of the difference between measurements and predictions will be presented for each model and for both the DBSG5 and the SRTM terrain profiles, as functions of their number of main obstacles. A better basis for comparison between predictions and experimental data was obtained from a special measurement series performed by HTI to determine the height function of the received field strength. These measurements will be described, also compared with model predictions and statistically analyzed.
IEEE Transactions on Antennas and Propagation, 2012
The effects from lateral variations of irregular terrain on the propagation of radio waves are co... more The effects from lateral variations of irregular terrain on the propagation of radio waves are considered by the representation of the vector fields in terms of two scalar Hertz potentials in spherical coordinates. The combination of three-dimensional parabolic equations for these potentials with an impedance boundary condition for the ground, followed by a transformation of variables, will define a boundary-condition problem characterized by equations displaying coefficients that depend on the terrain height function and its partial derivatives. The problem solution through the Crank-Nicolson scheme will lead to a sparse system of linear equations, which will be solved by a direct method. The resulting numerical model will be applied to test cases to show similar features to those from examples described in the literature, taken as references for validation purposes.
Many models have been proposed to represent diffraction effects on the propagation of radio waves... more Many models have been proposed to represent diffraction effects on the propagation of radio waves over irregular terrain in the VHF and UHF bands. Predictions from these models have been compared with results from associated field-strength measurements available in extensive databases that also incorporate the technical parameters of thousands of VHF and UHF links. Some possible sources of the still high values of the standard deviations of errors between predictions and measurements will be identified and discussed, with particular attention to uncertainties on digital elevation models and on the effective Earth's radius, as well as to effects from lateral propagation.
Thousands of path profiles incorporated into the ITU-R Study Group 3 (DBSG5) database and those e... more Thousands of path profiles incorporated into the ITU-R Study Group 3 (DBSG5) database and those estimated from the shuttle radar topography mission (SRTM) digital elevation model for the same terminal coordinates will be compared. Models that estimate diffraction effects on the propagation of radio waves over irregular terrain in the VHF and UHF bands available for digital TV applications will be used to predict field strengths that will be compared with those from the corresponding measurements. The mean value and the standard deviation of the difference between measurements and predictions will be presented for each model and for both the DBSG5 and the SRTM terrain profiles, as functions of their number of main obstacles. A better basis for comparison between predictions and experimental data was obtained from a special measurement series performed by HTI to determine the height function of the received field strength. These measurements will be described, also compared with model predictions and statistically analyzed.
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