comparative study of the commonly used methods for the prediction of the coverage area due to tra... more comparative study of the commonly used methods for the prediction of the coverage area due to transmitter operating at the HF band is presented. Those statistical model based tools are ITU's REC 533, Ionospheric Communication Analysis and Prediction Program; IONCAP, Voice of America's VOACAP and Ionospheric Communication Enhanced Profile Analysis and Circuit Prediction Program; ICEPAC. The received signal due to a typical transmitter located at Cricklade, England operating around 7.9 - 19.1 MHz (HF Band I) is computed as a function of frequency, time and the sunspot number. The ray tracing method calculates the virtual height. The calculated results are compared with the experimental data and the discrepancies are examined.
Bu çalışmada, TID oluşumlarını kestirmek amacıyla GPS kullanımı önerilmiştir. Bu amaçla, dörderli... more Bu çalışmada, TID oluşumlarını kestirmek amacıyla GPS kullanımı önerilmiştir. Bu amaçla, dörderli gruplar halinde altı farklı yörüngede dönmekte olan GPS uydularına ait uydu numarası, yörünge numarası ve zamanın fonksiyonu olan genlik dalgalanma indisi (f a) tanımlanmıştır. Bu indis dakikalık eğik TEC değerlerine ait değişimlerin mutlak değerinin ortancası olarak 15 dakikalık süreler içerisinde incelenmektedir. Daha sonra, f a değerleri kullanılarak her bir yörünge için saatlik değişimleri veren F a indisi hesaplamıştır. Sonuçlar F a değerinin 1,5'den büyük olması durumunda çok kuvvetli TEC değişimlerinin meydana geldiği ve sinyal kayıplarının yüksek olduğu; 0,5-1,0 arasında sinyal kayıplarının kabul edilebilir sınırlar içinde olduğu ve son olarak F a değerinin 0,5'ten küçük olduğu durumlarda ise haberleşme için ideal şartların var olduğunu göstermektedir.
In this study, the problem of model validation for the maritime infrared (IR) background radiance... more In this study, the problem of model validation for the maritime infrared (IR) background radiance is examined. The Data Acquisition Exercise (DAE) was executed from 2006 to 2008 and various radiometric data were collected. Measured data were acquired from the observing period conducted at a station located in the Marmara Sea region of Turkey. The simulated and the measured data are analyzed, and the comparisons are presented. The discrepancies are analyzed under different scenarios, and the effect of wind speed, fetch speed, wind direction and atmospheric conditions are studied. An approach for using the consistent error as the predictive error bias to calibrate the modeling in a predetermined scenario is proposed. The comparison results are given.
IEEE Antennas and Propagation Society International Symposium. 1998 Digest. Antennas: Gateways to the Global Network. Held in conjunction with: USNC/URSI National Radio Science Meeting (Cat. No.98CH36194), 1998
A comparative study of the commonly used methods for the prediction of the coverage area due to a... more A comparative study of the commonly used methods for the prediction of the coverage area due to a transmitter operating at the HF hand is presented. Those statistical model-based tools are Ionospheric Communication analysis and Prediction Program; IONCAP, Ionospheric Communication Enhanced Profile Analysis and Circuit Prediction Program; ICEPAC, Voice of America's VOACAP and ITU's REC 533, and those are illustrated
2011 IEEE 19th Signal Processing and Communications Applications Conference (SIU), 2011
In electro-optical and infrared end-to-end system analysis, the image degrading effects can be mo... more In electro-optical and infrared end-to-end system analysis, the image degrading effects can be modelled by cascaded linear shift invariant filters. These effects are in general listed as atmospheric effects, motion effects, optics, detector, reconstruction and display. The degrading effects simulation is discussed by using a developed basic simulator shortly and important points; sampling effects on restoration and shower curtain effects are pointed out. 1. GİRİŞ
IEEE International Geoscience and Remote Sensing Symposium, 2002
ABSTRACT The estimation of the electromagnetic propagation around a smooth spherical Earth in ano... more ABSTRACT The estimation of the electromagnetic propagation around a smooth spherical Earth in anomalous atmospheric conditions in the troposphere using Fourier split-step method is studied. The source of errors of Fourier split-step method and errors due to reducing the exact Helmholtz equation to the parabolic wave equation are reviewed. A quantitative measure for the accuracy of the numerical results is proposed. Optimization of the quantization parameters for accurate representation of electromagnetic propagation is investigated. The method is illustrated on different values of frequency, polarization, antenna pattern, antenna height, maximum angular frequency and range dependent refractivity. Optimal parameters are subsequently discussed. Finally, the region of validity is investigated numerically by comparison with the exact models.
IEEE International Geoscience and Remote Sensing Symposium, 2002
ABSTRACT The scintillation effects are known to degrade the tracking performance of a GPS receive... more ABSTRACT The scintillation effects are known to degrade the tracking performance of a GPS receiver. Possible Doppler shift observed on the GPS signal due to rapid phase variations could extend the bandwidth exceedingly, forcing the phase locked loop to its tracking limits, and the lost of signal can be observed especially at the frequency L2. For this, accurate estimation of the ionospheric irregularities is often not possible since ionosphere is usually assumed to be locally isotropic. In this study, short time (15 min.) amplitude fluctuation index (fa) that is function of time, orbit number and satellite number, and hourly amplitude fluctuation index (Fa) that function of hour and orbit number only, are defined. fa can be calculated at any point on the surface of the Earth for each 15 minute long time section using only one satellite, and Fa can be calculated hourly and using satellites in the vicinity of the receiver. It is shown that utilizing the amplitude fluctuation indices fa and Fa, oblique examination of the index is possible, without assuming a perfect vertical path. Finally, the variations on the total electron content corresponding to different cases are discussed on numerical results.
IEEE International Geoscience and Remote Sensing Symposium, 2002
ABSTRACT The seasonal, diurnal, latitudinal and longitudinal variations of ionospheric total elec... more ABSTRACT The seasonal, diurnal, latitudinal and longitudinal variations of ionospheric total electron content (TEC) is investigated using global ionospheric maps (GIM) corresponding to a twenty-four month period (1999-2000) at Ankara (39.88°N, 32.35°E), Turkey. The dependence of those TEC values on solar zenith angle and season is also examined. It is observed that the daily mean TEC values for one month are sufficient to extrapolate the corresponding values both for the previous and the following months. This is illustrated on interpolation for a whole twenty-four month period using only the daily mean values corresponding to February, May, August and November. It is interesting to note that the variations of solar and geomagnetic indices are reflected on the daily mean TEC values with a delay about 1 to 3 days and 1 to 2 days, respectively. It is also interesting to note that for the year 2000, winter anomaly was not concentrated in high midlatitudes as usually expected.
2007 3rd International Conference on Recent Advances in Space Technologies, 2007
Total Electron Content (TEC) is a key variable to measure the ionospheric characteristics and dis... more Total Electron Content (TEC) is a key variable to measure the ionospheric characteristics and disturbances. The I. INTRODUCTION Global Positioning System (GPS) can be used for TEC estimation Ionosphere forms the most important atmospheric layer for making use of the recorded signals at the GPS receiver. Reg-Est HF and satellite communication systems. Ionosphere varies method that is developed by F.Arikan, C.B. Erol and 0. Arikan with time, frequency, and location. Total Electron Content can be used to estimate high resolution, robust TEC values (TEC) provides a convenient measure for observing the combining GPS measurements of 30 s resolution obtained from variability of the ionosphere and characterization of the the satellites which are above the 10°elevation limit. Using this distortion on radio signals. TEC is defined as the total number method, it is possible to estimate TEC values for a whole day or a desired time period both for quiet and disturbed days of the of free electrons along a ray path of 1 m2 cross section. TEC is ionosphere. Reg-Est provides robust TEC estimates for high-closely related to solar and geomagnetic activities. TEC is latitude, mid-latitude and equatorial stations. In this study, some measured in TECU units (1 TECU =1016 el/2). The Global important parameters of Reg-Est such as ionospheric thin shell Positioning System (GPS), due to its availability for civilian height, weighting function and receiver-satellite biases are use in the last 10 years, provides a cost-effective alternative for investigated. By incorporating the results of the investigation, estimating TEC through recorded signals at the GPS receiver. Reg-Est algorithm is developed into IONOLAB method. Thin Although the ionospheric group delay or phase advance on the shell model height is an important parameter for Single Layer recorded GPS signals is a major source of positioning errors, Ionosphere Model (SLIM). In this study, it is shown that IONOLAB provides reliable and robust TEC estimates these parameters can be used to compute TEC efficiently. independent of the choice of the maximum ionization height
IEEE Transactions on Geoscience and Remote Sensing, 2000
The performance of infrared (IR) surveillance systems is proportional to the ability of distingui... more The performance of infrared (IR) surveillance systems is proportional to the ability of distinguishing the radiance of target from the background. In determining sea radiance as the background, experimental studies are incomplete and very expensive. The few simulation software packages that are available are limited to certain parameters and do not include all aspects of sea radiance. In this paper, simulation and analysis software, namely, InfrareD SeA Modeling and Analysis (DAMA), is developed to calculate the total radiance and its components seen by the observer. The DAMA software allows the user to define all possible parameters related to atmospheric conditions, sea surface conditions, and date and time of observation. The developed software includes all of the three major sea surface models in the IR band provided in the literature, namely, Cox and Munk, Mermelstein, and Shaw and Churnside models. In this sense, the DAMA software is unique in combining all possible atmospheric and surface parameters to provide components of total radiance. The DAMA software can be operated by a user-friendly graphical user interface to facilitate simulations and to analyze the outputs. For this paper, the software has been run for approximately 10 000 simulations to understand the behavior of maritime background in IR. The software is validated by the SEARAD software and measurement results. By this way, for the first time in the open literature, DAMA allows one to observe the behavior of total radiance and its components with respect to the variation of all possible input parameters.
4 comparative study of the commonly used methods for the prediction of the coverage area due to t... more 4 comparative study of the commonly used methods for the prediction of the coverage area due to transmitter operating at the HF band is presented. Those statistical model based tools are ITU's REC 533, Ionospheric Communication Analysis and Prediction Program; IONCAP, Voice of America's VOACAP and Ionospheric Communication Enhanced Profile Analysis and Circuit Prediction Program; ICEPAC. The received signal due to a typical transmitter located at Cricklade, England operating around 7.9-19.1 MHz (HF Band I) is computed as a function of frequency, time and the sunspot number. The ray tracing method calculates the virtual height. The calculated results are compared with the experimental data and the discrepancies are examined.
Variation of the atmospheric refraction index due to turbulent fluctuations is one of the key fac... more Variation of the atmospheric refraction index due to turbulent fluctuations is one of the key factors that affect the performance of electro-optical and infrared systems and sensors. Therefore, any prior knowledge about the degree of variation in the refractive index is critical in the success of field studies such as search and rescue missions, military applications, and remote sensing studies where these systems are used frequently. There are many studies in the literature in which the optical turbulence effects are modeled by estimation of the refractive index structure parameter, C(n)(2), from meteorological data for all levels of the atmosphere. This paper presents a modified approach for bulk-method-based C(n)(2) estimation. According to this approach, conventional wind speed, humidity, and temperature values above the surface by at least two levels are used as input data for Monin-Obukhov similarity theory in the estimation of similarity scaling constants with a finite difference approximation and a bulk-method-based C(n)(2) estimation. Compared with the bulk method, this approach provides the potential for using more than two levels of standard meteorological data, application of the scintillation effects of estimated C(n)(2) on the images, and a much simpler solution than traditional ones due to elimination of the roughness parameters, which are difficult to obtain and which increase the complexity, the execution time, and the number of additional input parameters of the algorithm. As a result of these studies, Atmospheric Turbulence Model Software is developed and the results are validated in comparison to the C(n)(2) model presented by Tunick.
Regularized estimation of Total Electron Content (Reg-Est) is a novel technique which can combine... more Regularized estimation of Total Electron Content (Reg-Est) is a novel technique which can combine signals from all the satellites for a given instant and given station and estimate the vertical TEC (VTEC) values for any desired period without missing any important features in the temporal or spatial domain. The preprocessed signals from all the satellites that are received for a certain time period are weighted according to their positions with respect to the local zenith. A two step regularization algorithm combines these signals and provides smooth VTEC estimates for the desired time period which can be as short as half an hour or as long as 24 h. The estimation algorithm is tried on VTEC values obtained from six midlatitude stations for the quiet and disturbed days of October, 2003. Within this period, the same estimation parameter set is used for all stations and time periods. When the regularized estimation results are compared with those from IRI-2001, JPL, CODE, UPC and ESA, best accordance is observed with JPL, UPC and CODE estimates. IRI computations usually provide a better fit for the night values. It is observed that the results from the regularized estimation algorithm are highly accurate in detecting disturbances and irregularities for various time scales and stations.
Computerized Ionospheric Tomography (CIT) is a method to investigate ionospheric electron density... more Computerized Ionospheric Tomography (CIT) is a method to investigate ionospheric electron density in two or three dimensions. CIT provides a flexible method for studying ionosphere. In CIT, GPS satellites and Earth based receivers are considered to perform tomographic reconstruction. The received signals are processed to calculate Total Electron Content (TEC). TEC values and the tomographic reconstruction algorithms are used together
IEEE Antennas and Propagation Society International Symposium. 2001 Digest. Held in conjunction with: USNC/URSI National Radio Science Meeting (Cat. No.01CH37229), 2001
comparative study of the commonly used methods for the prediction of the coverage area due to tra... more comparative study of the commonly used methods for the prediction of the coverage area due to transmitter operating at the HF band is presented. Those statistical model based tools are ITU's REC 533, Ionospheric Communication Analysis and Prediction Program; IONCAP, Voice of America's VOACAP and Ionospheric Communication Enhanced Profile Analysis and Circuit Prediction Program; ICEPAC. The received signal due to a typical transmitter located at Cricklade, England operating around 7.9 - 19.1 MHz (HF Band I) is computed as a function of frequency, time and the sunspot number. The ray tracing method calculates the virtual height. The calculated results are compared with the experimental data and the discrepancies are examined.
Bu çalışmada, TID oluşumlarını kestirmek amacıyla GPS kullanımı önerilmiştir. Bu amaçla, dörderli... more Bu çalışmada, TID oluşumlarını kestirmek amacıyla GPS kullanımı önerilmiştir. Bu amaçla, dörderli gruplar halinde altı farklı yörüngede dönmekte olan GPS uydularına ait uydu numarası, yörünge numarası ve zamanın fonksiyonu olan genlik dalgalanma indisi (f a) tanımlanmıştır. Bu indis dakikalık eğik TEC değerlerine ait değişimlerin mutlak değerinin ortancası olarak 15 dakikalık süreler içerisinde incelenmektedir. Daha sonra, f a değerleri kullanılarak her bir yörünge için saatlik değişimleri veren F a indisi hesaplamıştır. Sonuçlar F a değerinin 1,5'den büyük olması durumunda çok kuvvetli TEC değişimlerinin meydana geldiği ve sinyal kayıplarının yüksek olduğu; 0,5-1,0 arasında sinyal kayıplarının kabul edilebilir sınırlar içinde olduğu ve son olarak F a değerinin 0,5'ten küçük olduğu durumlarda ise haberleşme için ideal şartların var olduğunu göstermektedir.
In this study, the problem of model validation for the maritime infrared (IR) background radiance... more In this study, the problem of model validation for the maritime infrared (IR) background radiance is examined. The Data Acquisition Exercise (DAE) was executed from 2006 to 2008 and various radiometric data were collected. Measured data were acquired from the observing period conducted at a station located in the Marmara Sea region of Turkey. The simulated and the measured data are analyzed, and the comparisons are presented. The discrepancies are analyzed under different scenarios, and the effect of wind speed, fetch speed, wind direction and atmospheric conditions are studied. An approach for using the consistent error as the predictive error bias to calibrate the modeling in a predetermined scenario is proposed. The comparison results are given.
IEEE Antennas and Propagation Society International Symposium. 1998 Digest. Antennas: Gateways to the Global Network. Held in conjunction with: USNC/URSI National Radio Science Meeting (Cat. No.98CH36194), 1998
A comparative study of the commonly used methods for the prediction of the coverage area due to a... more A comparative study of the commonly used methods for the prediction of the coverage area due to a transmitter operating at the HF hand is presented. Those statistical model-based tools are Ionospheric Communication analysis and Prediction Program; IONCAP, Ionospheric Communication Enhanced Profile Analysis and Circuit Prediction Program; ICEPAC, Voice of America's VOACAP and ITU's REC 533, and those are illustrated
2011 IEEE 19th Signal Processing and Communications Applications Conference (SIU), 2011
In electro-optical and infrared end-to-end system analysis, the image degrading effects can be mo... more In electro-optical and infrared end-to-end system analysis, the image degrading effects can be modelled by cascaded linear shift invariant filters. These effects are in general listed as atmospheric effects, motion effects, optics, detector, reconstruction and display. The degrading effects simulation is discussed by using a developed basic simulator shortly and important points; sampling effects on restoration and shower curtain effects are pointed out. 1. GİRİŞ
IEEE International Geoscience and Remote Sensing Symposium, 2002
ABSTRACT The estimation of the electromagnetic propagation around a smooth spherical Earth in ano... more ABSTRACT The estimation of the electromagnetic propagation around a smooth spherical Earth in anomalous atmospheric conditions in the troposphere using Fourier split-step method is studied. The source of errors of Fourier split-step method and errors due to reducing the exact Helmholtz equation to the parabolic wave equation are reviewed. A quantitative measure for the accuracy of the numerical results is proposed. Optimization of the quantization parameters for accurate representation of electromagnetic propagation is investigated. The method is illustrated on different values of frequency, polarization, antenna pattern, antenna height, maximum angular frequency and range dependent refractivity. Optimal parameters are subsequently discussed. Finally, the region of validity is investigated numerically by comparison with the exact models.
IEEE International Geoscience and Remote Sensing Symposium, 2002
ABSTRACT The scintillation effects are known to degrade the tracking performance of a GPS receive... more ABSTRACT The scintillation effects are known to degrade the tracking performance of a GPS receiver. Possible Doppler shift observed on the GPS signal due to rapid phase variations could extend the bandwidth exceedingly, forcing the phase locked loop to its tracking limits, and the lost of signal can be observed especially at the frequency L2. For this, accurate estimation of the ionospheric irregularities is often not possible since ionosphere is usually assumed to be locally isotropic. In this study, short time (15 min.) amplitude fluctuation index (fa) that is function of time, orbit number and satellite number, and hourly amplitude fluctuation index (Fa) that function of hour and orbit number only, are defined. fa can be calculated at any point on the surface of the Earth for each 15 minute long time section using only one satellite, and Fa can be calculated hourly and using satellites in the vicinity of the receiver. It is shown that utilizing the amplitude fluctuation indices fa and Fa, oblique examination of the index is possible, without assuming a perfect vertical path. Finally, the variations on the total electron content corresponding to different cases are discussed on numerical results.
IEEE International Geoscience and Remote Sensing Symposium, 2002
ABSTRACT The seasonal, diurnal, latitudinal and longitudinal variations of ionospheric total elec... more ABSTRACT The seasonal, diurnal, latitudinal and longitudinal variations of ionospheric total electron content (TEC) is investigated using global ionospheric maps (GIM) corresponding to a twenty-four month period (1999-2000) at Ankara (39.88°N, 32.35°E), Turkey. The dependence of those TEC values on solar zenith angle and season is also examined. It is observed that the daily mean TEC values for one month are sufficient to extrapolate the corresponding values both for the previous and the following months. This is illustrated on interpolation for a whole twenty-four month period using only the daily mean values corresponding to February, May, August and November. It is interesting to note that the variations of solar and geomagnetic indices are reflected on the daily mean TEC values with a delay about 1 to 3 days and 1 to 2 days, respectively. It is also interesting to note that for the year 2000, winter anomaly was not concentrated in high midlatitudes as usually expected.
2007 3rd International Conference on Recent Advances in Space Technologies, 2007
Total Electron Content (TEC) is a key variable to measure the ionospheric characteristics and dis... more Total Electron Content (TEC) is a key variable to measure the ionospheric characteristics and disturbances. The I. INTRODUCTION Global Positioning System (GPS) can be used for TEC estimation Ionosphere forms the most important atmospheric layer for making use of the recorded signals at the GPS receiver. Reg-Est HF and satellite communication systems. Ionosphere varies method that is developed by F.Arikan, C.B. Erol and 0. Arikan with time, frequency, and location. Total Electron Content can be used to estimate high resolution, robust TEC values (TEC) provides a convenient measure for observing the combining GPS measurements of 30 s resolution obtained from variability of the ionosphere and characterization of the the satellites which are above the 10°elevation limit. Using this distortion on radio signals. TEC is defined as the total number method, it is possible to estimate TEC values for a whole day or a desired time period both for quiet and disturbed days of the of free electrons along a ray path of 1 m2 cross section. TEC is ionosphere. Reg-Est provides robust TEC estimates for high-closely related to solar and geomagnetic activities. TEC is latitude, mid-latitude and equatorial stations. In this study, some measured in TECU units (1 TECU =1016 el/2). The Global important parameters of Reg-Est such as ionospheric thin shell Positioning System (GPS), due to its availability for civilian height, weighting function and receiver-satellite biases are use in the last 10 years, provides a cost-effective alternative for investigated. By incorporating the results of the investigation, estimating TEC through recorded signals at the GPS receiver. Reg-Est algorithm is developed into IONOLAB method. Thin Although the ionospheric group delay or phase advance on the shell model height is an important parameter for Single Layer recorded GPS signals is a major source of positioning errors, Ionosphere Model (SLIM). In this study, it is shown that IONOLAB provides reliable and robust TEC estimates these parameters can be used to compute TEC efficiently. independent of the choice of the maximum ionization height
IEEE Transactions on Geoscience and Remote Sensing, 2000
The performance of infrared (IR) surveillance systems is proportional to the ability of distingui... more The performance of infrared (IR) surveillance systems is proportional to the ability of distinguishing the radiance of target from the background. In determining sea radiance as the background, experimental studies are incomplete and very expensive. The few simulation software packages that are available are limited to certain parameters and do not include all aspects of sea radiance. In this paper, simulation and analysis software, namely, InfrareD SeA Modeling and Analysis (DAMA), is developed to calculate the total radiance and its components seen by the observer. The DAMA software allows the user to define all possible parameters related to atmospheric conditions, sea surface conditions, and date and time of observation. The developed software includes all of the three major sea surface models in the IR band provided in the literature, namely, Cox and Munk, Mermelstein, and Shaw and Churnside models. In this sense, the DAMA software is unique in combining all possible atmospheric and surface parameters to provide components of total radiance. The DAMA software can be operated by a user-friendly graphical user interface to facilitate simulations and to analyze the outputs. For this paper, the software has been run for approximately 10 000 simulations to understand the behavior of maritime background in IR. The software is validated by the SEARAD software and measurement results. By this way, for the first time in the open literature, DAMA allows one to observe the behavior of total radiance and its components with respect to the variation of all possible input parameters.
4 comparative study of the commonly used methods for the prediction of the coverage area due to t... more 4 comparative study of the commonly used methods for the prediction of the coverage area due to transmitter operating at the HF band is presented. Those statistical model based tools are ITU's REC 533, Ionospheric Communication Analysis and Prediction Program; IONCAP, Voice of America's VOACAP and Ionospheric Communication Enhanced Profile Analysis and Circuit Prediction Program; ICEPAC. The received signal due to a typical transmitter located at Cricklade, England operating around 7.9-19.1 MHz (HF Band I) is computed as a function of frequency, time and the sunspot number. The ray tracing method calculates the virtual height. The calculated results are compared with the experimental data and the discrepancies are examined.
Variation of the atmospheric refraction index due to turbulent fluctuations is one of the key fac... more Variation of the atmospheric refraction index due to turbulent fluctuations is one of the key factors that affect the performance of electro-optical and infrared systems and sensors. Therefore, any prior knowledge about the degree of variation in the refractive index is critical in the success of field studies such as search and rescue missions, military applications, and remote sensing studies where these systems are used frequently. There are many studies in the literature in which the optical turbulence effects are modeled by estimation of the refractive index structure parameter, C(n)(2), from meteorological data for all levels of the atmosphere. This paper presents a modified approach for bulk-method-based C(n)(2) estimation. According to this approach, conventional wind speed, humidity, and temperature values above the surface by at least two levels are used as input data for Monin-Obukhov similarity theory in the estimation of similarity scaling constants with a finite difference approximation and a bulk-method-based C(n)(2) estimation. Compared with the bulk method, this approach provides the potential for using more than two levels of standard meteorological data, application of the scintillation effects of estimated C(n)(2) on the images, and a much simpler solution than traditional ones due to elimination of the roughness parameters, which are difficult to obtain and which increase the complexity, the execution time, and the number of additional input parameters of the algorithm. As a result of these studies, Atmospheric Turbulence Model Software is developed and the results are validated in comparison to the C(n)(2) model presented by Tunick.
Regularized estimation of Total Electron Content (Reg-Est) is a novel technique which can combine... more Regularized estimation of Total Electron Content (Reg-Est) is a novel technique which can combine signals from all the satellites for a given instant and given station and estimate the vertical TEC (VTEC) values for any desired period without missing any important features in the temporal or spatial domain. The preprocessed signals from all the satellites that are received for a certain time period are weighted according to their positions with respect to the local zenith. A two step regularization algorithm combines these signals and provides smooth VTEC estimates for the desired time period which can be as short as half an hour or as long as 24 h. The estimation algorithm is tried on VTEC values obtained from six midlatitude stations for the quiet and disturbed days of October, 2003. Within this period, the same estimation parameter set is used for all stations and time periods. When the regularized estimation results are compared with those from IRI-2001, JPL, CODE, UPC and ESA, best accordance is observed with JPL, UPC and CODE estimates. IRI computations usually provide a better fit for the night values. It is observed that the results from the regularized estimation algorithm are highly accurate in detecting disturbances and irregularities for various time scales and stations.
Computerized Ionospheric Tomography (CIT) is a method to investigate ionospheric electron density... more Computerized Ionospheric Tomography (CIT) is a method to investigate ionospheric electron density in two or three dimensions. CIT provides a flexible method for studying ionosphere. In CIT, GPS satellites and Earth based receivers are considered to perform tomographic reconstruction. The received signals are processed to calculate Total Electron Content (TEC). TEC values and the tomographic reconstruction algorithms are used together
IEEE Antennas and Propagation Society International Symposium. 2001 Digest. Held in conjunction with: USNC/URSI National Radio Science Meeting (Cat. No.01CH37229), 2001
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