New Publications are available for Ionospheric electromagnetic wave propagation
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New Publications are available now online for this publication.
Please follow the links to view the publication.Analysis of Chilton ionosonde critical frequency measurements during solar cycle 23 in the context of midlatitude HF NVIS frequency predictions
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0373
This paper presents a comparison of Chilton ionosonde critical frequency measurements against vertical-incidence HF propagation predictions using ASAPS (Advanced Stand Alone Prediction System) and VOACAP (Voice of America Coverage Analysis Program). This analysis covers the time period from 1996 to 2010 (thereby covering solar cycle 23) and was carried out in the context of UK-centric near-vertical incidence skywave (NVIS) frequency predictions. Measured and predicted monthly median frequencies are compared, as are the upper and lower decile frequencies (10% and 90% respectively). The ASAPS basic MUF predictions generally agree with fxI (in lieu of fxF2) measurements, whereas those for VOACAP appear to be conservative for the Chilton ionosonde, particularly around solar maximum. Below ~4 MHz during winter nights around solar minimum, both ASAPS and VOACAP MUF predictions tend towards foF2, which is contrary to their underlying theory and requires further investigation. While VOACAP has greater errors at solar maximum, those for ASAPS increase at low or negative T-index values. Finally, VOACAP errors might be large when T-SSN exceeds ~15. (6 pages)The synthetic aperture radar trans- ionospheric radio propagation simulator (SAR-TIRPS)
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.0046
Space-based synthetic aperture radars (SAR) operating below 1 GHz are subject to forward scattering by ionospheric irregularities. This limits the synthetic aperture and bandwidth over which phase coherence can be maintained. This paper describes the SAR trans-ionospheric radio propagation simulator (SAR-TIRPS), a phase screen model which simulates ionosphere-corrupted SAR images of point targets. The Parabolic Equation propagation method allows both phase and amplitude fluctuations to be modelled. Background Total Electron Content (TEC) is modelled as an additional frequency-dependent phase shift. Examples are presented of L-band and P-band SAR simulations, showing how the target image and derived quantities (sidelobe ratios along- and cross-track) vary with changing ionospheric phase spectrum parameters. SAR-TIRPS proves to be a useful tool in assessing design concepts for low-frequency space radars.Advances in ionospheric propagation modelling at high-latitudes
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.0029
Many services rely on the output of propagation planning tools to predict the future state of the ionosphere and the availability of suitable communications channels. While this approach is adequate for services operating at high-latitudes during quiet ionospheric conditions it is insufficient to deal with a disturbed ionosphere. This paper presents the results of empirical modelling of the changes that occur in the D- and E-regions of the ionosphere following the onset of disturbed conditions as defined by the occurrence of a storm sudden commencement.The extraordinary wave mode: neglected in current practical literature for HF NVIS communications
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.0028
Current practical literature for HF NVIS communication places significant emphasis on foF2 as being the maximum frequency for vertical propagation. This, however, fails to consider the extraordinary wave. This paper presents the analysis of 5 MHz beacon data, showing the relevance of the extraordinary wave in the MUF calculation for NVIS propagation. The results are in full agreement with established scientific theory and ionospheric propagation prediction methods, the detail of which the HF NVIS user community may not be aware of.Comparison of oblique sounding measurements and VOACAP predictions on a mid-latitude path
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.0036
Observations of the MUF measured on a mid-latitude path are compared to predictions made by VOACAP. In general, 80% of the observations are within a few MHz of the prediction, although the presence of sporadic E or rapidly changing ionisation at sunrise and sunset leads to a much poorer prediction. The median observed MUF decreases from about 19 MHz to less than 14.5 MHz as kp increases from 0 to 6.Spatial decorrelation of VHF and UHF trans-ionospheric signals measured at Ascension island
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.0047
The effect of spatial decorrelation of signals of space-based synthetic-aperture radars by equatorial ionospheric turbulence, is studied by monitoring 150 and 400 MHz signals from LEO beacon satellites on an array of spaced antennas located on Ascension Island, and analysing the cross-correlations of the phases of the received signals. The special property of this approach is that it does not convolve the spatial fluctuations with the movement of the satellite. The geometrical component of the phase difference between antennas is accurately removed by adjusting the satellite position using the measured phases. As expected, the phase of VHF signals is much more affected by scintillation than the UHF phase. In the example given, the spatial correlation over 130 m falls to zero at VHF and 0.55 at UHF. Correlations over longer distances have been determined using a novel 'phase reconstruction' technique. In the absence of scintillation the decorrelation distance is ~10 km for both frequencies; with increasing scintillation, it decreases to around 100 m at VHF and 300 m at UHF.Principal component analysis of sub-ionospheric propagation conditions
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.0041
Very Low Frequency (VLF) waves propagate with insignificant attenuation in the Earth-ionosphere waveguide. Attenuation is, however, relatively higher on illuminated paths due to the presence of the ionospheric D region. Sub-ionospheric propagation conditions may be monitored using a narrowband receiver tuned to the stable signals from numerous VLF transmitters distributed across the surface of the Earth. The passage of the day-night terminator across the transmitter-receiver path has a characteristic signature in the amplitude and phase of the signal. Principal Component Analysis (PCA) was applied to distinguish between this regular diurnal pattern and exogenous perturbations.Effects of ionospheric small-scale structures on GNSS
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.0062
This paper presents a statistical study of ionospheric small- scale structures detected at the GPS station of Brussels (BRUS) from 1994 to 2008. Two types of structures have been detected: Travelling Ionospheric Disturbances (TID's) and so- called "Noise-Like Structures" due to geomagnetic storms. The influence of such structures on differential positioning like Real-Time Kinematic (RTK) have been explored: the positioning error due to the ionosphere is larger during geomagnetic storms than during the occurrence of TID's. Maximum values observed for a baseline of 11 km are respectively 65 cm and 15 cm.Numerical simulation of ionospheric propagation based on the TSNU-PSTD
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.1297
The finite difference time domain (FDTD) method for solving ionospheric propagation will waste great time and memory. In this paper, a transformed-space non-uniform pseudo-spectral time domain (TSNU-PSTD) method in cold plasma is developed and applied to the simulation of ionospheric propagation. It is reported that this technique is as efficient as the conventional uniform pseudo-spectral time domain(PSTD) with a computational complexity of O(NIogN) since the difference is only the factor of du/dz between the conventional PSTD and the TSNU-PSTD techniques. And TSNU-PSTD can eliminate undesired Gibbs phenomena on the interface of each layer of ionosphere, which could seriously deteriorate the implementation of the PSTD.Modelling of AGW/TIDs and raytracing through the ionosphere
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.0026
Refraction of HF waves in the ionosphere enables worldwide communication with low energies. But HF waves are deviated from great circle path propagation by gradients of the electron density of the ionosphere. To enhance the accuracy of HF direction finding the error due to lateral gradients of the electron density of the ionosphere has to be specified. Thus the ionosphere disturbed by atmospheric gravity waves (AGWs) has been modelled and a raytracing of the HF waves have been conducted.The equatorial scintillations and space weather effects on its generation during geomagnetic storms
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.0071
Great diversity of the ionospheric phenomena leads to a variety of irregularity types with spatial size from many thousands of kilometers to few centimeters and lifetimes from days to fractions of second. Since the ionosphere strongly influences the propagation of radio waves, signal distortions caused by these irregularities affect short-wave transmissions on Earth, transionospheric satellite communications and navigation. In this work the solar wind and the equatorial ionosphere parameters, Kp, Dst, AU, AL indices characterized contribution of different magnetospheric and ionospheric currents to the H-component of geomagnetic field are examined to test the space weather effect on the generation of ionospheric irregularities producing VLF scintillations. According to the results of the current statistical studies, one can predict scintillations from Aarons' criteria using the Dst index, which mainly depicts the magnetospheric ring current field. To amplify Aarons' criteria or to propose new criteria for predicting scintillation characteristics is the question. In the present phase of the experimental investigations of electron density irregularities in the ionosphere new ways are opened up because observations in the interaction between the solar wind-magnetosphere-ionosphere during magnetic storms have progressed greatly. We have examined scintillation relation to magnetospheric and ionospheric currents and show that the factor, which presents during magnetic storms to fully inhibit scintillation, is the positive Bz-component of the IMF. During the positive Bz IMF F layer cannot raise altitude where scintillations are formed. The auroral indices and Kp do better for the prediction of the ionospheric scintillations at the equator. The interplanetary magnetic field data and models can be used to explain the relationship between the equatorial ionospheric parameters, h'F, f<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">0</sub>F2, and the equatorial geomagnetic variations with the polar ionosphere currents and the solar wind. Taking into account the time delay between the solar wind and the ionosphere phenomena, the relationship between the solar wind and the ionosphere parameters can be used for predicting of scintillations.Determination of higher order ionospheric contributions from Giove signals
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.0064
Next generation GNSS systems will make triple-frequency signals available in a near future. Such systems have the potential to allow for the determination of the second order ionospheric error term. However, the direct estimate of the second order term from triple-frequency measurements may present severe limitations due to tracking noise problems. A measurement campaign has been undertaken in 2007 in Brest to receive signals from the Giove-A experimental satellite. Based on these data, it is shown that a semi-empirical model can be effectively used to derive ionospheric higher order terms from the phase measurements. The model is briefly described and it is shown that a satisfactory noise level is observed on the results. It is thus anticipated that the proposed procedure will offer a practical way to correct future Galileo measurements for ionospheric higher order errors.Ionosphere-induced first and higher order errors for space based SAR
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.0048
Satellite borne SARs need to be operated at low frequencies (HF, VHF) to obtain good penetration through vegetation. At these lower frequencies the effect of the ionosphere is appreciable and the phase variation (in radians) with frequency is higher order than f <sup xmlns="http://pub2web.metastore.ingenta.com/ns/">-1</sup>. The magnitude of these higher order phase terms in f <sup xmlns="http://pub2web.metastore.ingenta.com/ns/">-2</sup> and f <sup xmlns="http://pub2web.metastore.ingenta.com/ns/">-3</sup> (in radians) are determined for all frequencies between 50 and 100 MHz for both magneto-ionic modes and for a range of elevations and azimuths (with respect to the magnetic meridian), time of day, month of the year and R12. Calculations are performed for a realistic 3D electron density distribution including both vertical and horizontal gradients of electron density (given by the NeQuick model) to assess accurately these higher order terms for a SAR at 600 km altitude for different ionospheric conditions.Night-time sporadic E measurements on an oblique path along the mid-latitude trough at sunspot minimum and sunspot maximum
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.0039
Results are presented of the night-time occurrence of sporadic E on a path tangential to the mid-latitude trough under conditions of sunspot maximum and sunspot minimum, and for different levels of geomagnetic activity. Sporadic E was observed more often at sunspot minimum and when kp was high (>5). For kps5, at sunspot minimum sporadic E is observed less frequently with increasing kp, while the opposite is the case at sunspot maximum.Large and mid-scale ionospheric perturbation characteristics deduced from GNSS measurements
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.0065
Large and mid- scale ionospheric perturbations are closely related to complex solar-terrestrial interactions in the course of space weather events. Ground and space based dual frequency measurements of Global Navigation Satellite Systems (GNSS) have been used over more than one solar cycle in order to derive characteristics of ionospheric storms. Whereas the ground based measurements show strong horizontal redistribution of plasma during ionospheric storms, the space borne measurements indicate severe vertical redistribution of the ionospheric plasma during selected space weather events. Storm enhanced spatial gradients are related to strong plasma convection as well as ion outflow in the plasmasphere. Ionization fronts and wavelike perturbation processes propagate predominantly from high to mid-latitudes with a speed ranging from 200-1000 m/s. Spatial gradients may reach values of 50 mm/km which may seriously affect precise and safety-critical GNSS applications. Equatorward Travelling Ionospheric Disturbances (TIDs) are characterized by wavelengths in the order of 2000 km, a mean period of 59 minutes and a mean phase speed of about 680 m/s.Study of some unusual VLF emissions
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.0088
The study of very low frequency (VLF) emissions has been conducted for many years, and has resulted in numerous publications. A few emission types, such as whistlers (electromagnetic signals generated by lightning, and dispersed on their path through the magnetosphere) and chorus (the result of Doppler shifted cyclotron resonance interactions in the magnetosphere), are already well understood. However, many other emissions are not well explained, mainly due to their infrequent occurrence. These emissions typically occur at frequencies below 4 kHz, can be periodic (with periods mostly in the range 2 s to 5 s), and are believed to be generated by some form of instability. These extraordinary emissions, as well as geomagnetic conditions at the time of their occurrence, are discussed.Ionospheric mapping and radio tomography
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.0027
Results of radio tomographic studies of the ionosphere in different latitudinal and longitudinal regions in the world under various solar and geophysical conditions are discussed. Modern methods of satellite ionospheric tomography are described (low orbital, LO, and high orbital, HO, radio tomography), advantages and limitations of these two techniques are compared. Examples of 2D LORT, 3D and 4D HORT ionospheric images are shown. Method of combined radio tomography involving both LORT and HORT and including elements of radio occultation (RO) technoque is considered. Results obtained with combined radio tomography are discussed.HF radar observation of ionospheric irregularities with unusual behaviour
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.0022
HF radar ionospheric echoes have been observed at mid latitudes, exhibiting a very unusual behaviour in the RTI (Range-Time-Intensity) display with fast quasi-periodic variations of the power of the echoes in the range 1-10 seconds. A wavelet analysis reveals that periodicities are in fact present in the data ranging from 1 second up to 400 seconds, depending on the time of observation. The strongest radar echoes were recorded during the first 40 minutes of the experiment. The radar used for these observations offers the possibility to perform scanning in elevation and in azimuth by software. Elevation scans have been used to estimate the height of the echoing region. Apparently the echoes are not coming exactly from the aspect-sensitive region. This result must be considered carefully because at HF frequencies refraction of radio waves easily produces ray bending.First results from the Cyprus digisonde
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.0024
A new ionospheric station was recently established in Nicosia (Cyprus) to initiate ionospheric research on the island. The deployment of a DPS-4D (digisonde) developed at the University of Massachusetts Lowell's Center for Atmospheric Research (UMLCAR), is considered very beneficial to the ionospheric scientific community, taking into account the lack of adequate scientific infrastructure, especially at low latitudes of the European sector, for continuous monitoring. Its operation will contribute to international networks for ionospheric nowcasting and forecasting and to the enhancement and validation of ionospheric models in the eastern Mediterranean region. In this paper results in terms of ionograms and scaled parameters, will be presented and briefly discussed.Study of ionospheric irregularities over near-equatorial station Anantapur using VHF scintillations
http://dl-live.theiet.org/content/conferences/10.1049/ic_20070752
An essential component of the ionosphere is a small-scale electron density structure that causes scintillations (fluctuations in amplitude and phase) of radio waves on transionospheric links. The study of these radio wave scintillations plays an important role in understanding the basic mechanism responsible for the generation and movement of ionospheric irregularities and their characteristics. This knowledge is very much essential for planning and development of satellite based communication system and radar system. In this paper we present our work on VHF amplitude Scintillations recorded at 250.649 MHz from FLEETSAT satellite using i-com receiver during March-2005 to August-2006 at Anantapur (14.7°N, 77.7°E, and Dip 15.4°N) India, that have been analyzed to study Ionospheric irregularities during day time and night time. Also the role of geo-magnetic activity on the enhancement and suppression of Ionospheric irregularities during quiet and disturbed days are clearly depicted in our work. We also present the results of observation of the diurnal and seasonal variations in the occurrence of the scintillations. The obtained results are discussed in the light of recent observations.Satellite ionosphere monitoring from ultralow heights
http://dl-live.theiet.org/content/conferences/10.1049/ic.2007.1426
The processing of radio sounding results from the "Mir" station during the periods when it was below the F2 layer maximum had shown the existence of new, previously unknown trace on ionograms called retarded lower traces (RLT). The analysis of this trace lead to a hypothesis according to which in conditions of such an ionosphere uncommon trajectories of many frequencies come into existence, which after the inclined reflection from Earth interact with sharp gradients of electron density in the ionosphere and as a result of this interaction return back to the satellite. The analysis of these ionograms gives an opportunity to construct the distribution of the isoelectronic surfaces inside of ionosphere irregularities. The results of mathematical modelling of the experiment are presented in the paper. The method of characteristic, is used for ray tracing calculations. Additionally, the height analysis was held, wherein the position of the satellite was varied in order to understand the behaviour of the returned trajectories and to locate optimal heights to receive ionograms with such traces during satellite ionosphere sounding. (6 pages)The effect of geomagnetic activity on the channel scattering functions of HF signals propagating at Northerly latitudes
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060305
In this paper, parameters derived from the observations of the channel scattering functions and azimuth of arrival for HF signals propagating over two paths (one in the auroral zone, and one at latitudes affected by the mid-latitude trough) are presented. In particular, the effects of geomagnetic activity (Kp) are considered, although the effects of season, time of day, and operating frequency are also discussed. For the mid-latitude trough path, there are some significant effects with Kp, while for the auroral path this is not the case.Wideband modelling and measurement of trans-ionospheric radar waveform propagation
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060288
A propagation model has been developed to simulate the corruption of wideband radio waveforms (such as radar chirps) as they pass through a non-homogeneous ionosphere. The ionosphere is modelled by a series of phase changing screens and a split-step parabolic equation method is used to describe the propagation of the complex electromagnetic field in planes normal to the propagation vector. Wideband characteristics of the channel are calculated by propagating spectral components of the waveform spectrum through the phase screens and then reconstituting the signal at the ground via a Fourier transformation into the time (delay) domain. By estimating the ionospheric drift velocity, the channel scattering function (signal power vs Doppler frequency and time delay) is calculated for a given satellite orbit and pulse repetition frequency (PRF).Investigation on fading of high frequency radio signals propagating in the ionosphere - results from a Jindalee radar experiment
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060243
High-frequency (HF) radio-wave propagation in the ionosphere is still widely used. The ability to measure and understand the behaviour of the channel, and the knowledge of how the channel will affect the propagating signals, is imperative to ensure the reliability, and maintain adequate performance, of modern wide-bandwidth HF systems. An experiment to study the fading of HF signals propagating in the ionosphere has been conducted. Using the Jindalee over-the-horizon (OTH) radar, the behaviour of the ionospheric channel and wide bandwidth signal fading were observed. In this paper results from the experiment will be presented, and the potential uses for the set of experimental data will be discussed.A model for time and frequency spreading of HF radio signals propagating through the equatorial ionosphere
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060248
An essential part of a method for the prediction of reliability of a digital communication system at HF, is the inclusion of a model for post-sunset scattering of signals in both the time and frequency domains. Although models have been developed for trans-ionospheric scintillation, little quantitative data is available for terrestrial systems. This paper proposes a model and indicates a procedure for the inclusion of scattering in the estimation of reliability.Satellite radiosounding of the ionosphere from heights near to a maximum of F2 layer
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060298
The generalized results and experience in the field of carrying out the experiments on the ionosphere radio sounding at the "MIR" manned space station (heights 340-390 km) are presented and analyzed. New multi frequency paths for radio wave propagation between the satellite and Earth, new data about the local specific macro irregularity in ionosphere and an adaptation of the IRI model by experimental data and some other factors were shown.Directional spread characteristics of HF signals received over paths within the auroral zone
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060309
The ionosphere within and close to the auroral zones is a dynamic propagation medium that is not perfectly horizontally stratified, and consequently the signals associated with each propagation mode may arrive at the receiver over a range of angles in both azimuth and elevation. In order to better understand this type of propagation, measurements have recently been made over two paths: (a) from Svalbard to Kiruna, Sweden, and (b) from Kirkenes, Norway to Kiruna. An analysis of these data is presented in this paper. The directional characteristics are summarised, and consideration given to modelling the propagation effects in the form of a channel simulator suitable for the testing of new equipment and processing algorithms.Propagation related measurements during three solar eclipses in Turkey
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060249
In this work, we would like to report three different measurements in the years of 1976, 1999, and 2006, relevant to the ionospheric radio propagation. They are different in temporal and spatial coordinates. During the recent total solar eclipse on 29 March 2006, high frequency (HF) signals are received in Antalya (36.9°N, 30.7°E), Turkey. The channel occupancy and atmospheric noise measurements over the HF band before, during, and after the solar eclipse are obtained.Wuhan ionospheric oblique backscattering sounding system (WIOBSS): system description and initial results
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060278
The Wuhan ionospheric oblique backscattering sounding system (WIOBSS) used for ionospheric research was established in Wuhan Hubei, China (30.35°N, 114.33°E). WIOBSS is a monostatic pulse Doppler radar using interpulse phase codes and pulse compression for good sensitivity. The operating frequency of WIOBSS is optional in MF and HF band. The peak power of the pulse is no more than 500 W. There are two basic sounding modes, fixed frequency and sweep frequency modes. The ionospheric bitemporal response and scattering function can be measured in real time and the Doppler ionogram drawn by scattering function includes the information of group delay, multipath, Doppler frequency shift and spread with high resolution. Furthermore, a theory for measuring the phase data of backscattering echo based on pulse compression system is put forward and applied to WIOBSS.Absorption of radio transmissions near the geomagnetic equator at medium frequencies
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060297
Electromagnetic waves entering the ionosphere are split by the Earth's magnetic field into two "characteristic waves", the ordinary wave (O-wave), and the extra-ordinary wave (X-wave) which suffers heavy absorption at medium frequencies (MF). This paper provides the basis for software to predict the polarisation match for a transmit antenna, and reviews initial measurements made near the geomagnetic dip equator.Simulation model of ionospheric radiochannel HF field
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060307
The paper presents experience of construction and operation of mathematical models (2-D, 3-D) which simulate decametre wave field on the basis of a structural-physical approach. The models allow obtaining complete representation of space-time and polarization structure of HF field at a reception site for specific geophysical conditions at a propagation path.An Antarctica to Spain HF link: oblique sounding results
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060310
Our Research Group in Electromagnetism and Communications is involved in a project dealing with the channel characterization and data transmission from the Spanish Antarctic Base (62.6S, 60.4W) to Spain (40.8N, 0.5E). In this paper the results of the third sounding survey corresponding to 22 consecutive days from January to February 2006 are presented. Frequencies in the range from 4 to 18 Mhz, and bandwidths up to 16.5 Khz have been probed. Results in terms of propagation losses, delay and Doppler spreads and signal to noise and interference ratio are summarized.First ionospheric monitoring campaign at Fraser's Hill Malaysia
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060258
The ionosphere over Malaysia is unique because of her location near the equator where the existence of the equatorial anomaly, electrojet, and fountain effect have made it good for studies. As part of a rejuvenation process in investigating the equatorial ionosphere in Malaysia, a short duration ionospheric experimental campaign was carried out at Fraser's Hill (lat. 3° 42.9' N, long. 101° 44.2' E, at an altitude of 1298 m) from August 1 to 18, 2005. Two sets of equipment were installed; a digital ionosonde and a dual frequency GPS receiver. The ionosonde consists of the sounding equipment using a delta antenna for transmitting and a dipole antenna for receiving. The GPS dual frequency receiver that is co-located with the digisonde is utilized as an ionospheric scintillation and TEC monitor. Results are compared with the main observatory at Parit Raja (lat. 1° 86' N, long. 103° 8' E) Malaysia.Multi-frequency satellite beacons and receivers for ionospheric irregularity imaging
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060266
A new set of satellite radio beacons called the coherent electromagnetic radio tomography (CERTO) should be available in 2006 and 2007 for measurements of ionospheric total electron content and radio scintillations. The CERTO beacons transmit unmodulated radio waves at VHF, UHF and L-Band frequencies. A fixed ratio of 3/8 is used between successive frequencies. Total electron content (TEC) is obtained using the differential phase technique. The radio scintillation effects caused by diffraction when propagating through ionospheric irregularities are investigated over a wide frequency range with the CERTO transmissions. All of the CERTO beacons are in low Earth orbit (LEO) with satellite inclinations ranging from 13 to 98 degrees. Each satellite that carries CERTO has other plasma sensors that complement the beacon data. In addition, a scintillation and tomography receiver in space (CITRIS) instrument will be launched in late 2006 to detect signals from the CERTO beacons and from the array of 56 DORIS VHF/S-Band radio beacons placed around the word by the French CNES. CITRIS will record ionospheric occupations and radio scintillations using a unique LEO geometry between satellites and between the ground and space. New algorithms have been developed for the multi-frequency CERTO and CITRIS data to provide TEC and scintillation data with greater accuracy than previously obtained with dual-band beacons. The data from the beacon receivers will be used to update space weather models.Transionospheric simulator for strong scintillation conditions and its use in quantifying scintillation effects for GNSS systems
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060261
A transionospheric propagation model has also been developed which can calculate frequency spectra (power spectra) of the phase and level (log-amplitude) fluctuations in a transionospheric channel of propagation containing time-varying electron density irregularities which produce scintillations and is valid even for strong scintillation conditions. Computer codes have been created to calculate time correlation functions of the phase and log-amplitude fluctuations for real 3D models of the background ionosphere and the anisotropic inverse power law spatial spectrum of fluctuations of the electron density of the ionosphere. Calculated power spectra of these processes can then be employed to produce random time sequences of the log-amplitude and phase of the field. Examples of simulations and their use are presented for both weak and strong scintillation conditions.Comparison between the measured and predicted parameters of HF radio signals propagating in the polar cap
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060308
In this paper, a statistical analysis of the observations of HF signals propagating over two paths, one that crosses the auroral oval and one in the polar cap, are compared to the predictions given by VOACAP. Large deviations in the azimuth of arrival were observed on both paths with upper-decile values of 90° for the trans-auroral oval path, and 70° for the polar cap path. For the trans-auroral path, VOACAP generally underestimates the signal strength in the presence of off-great circle propagation, while for the polar cap path, the signal strength is underestimated when VOACAP predicts propagation via a 2E mode that does not occur.Case studies of enhanced E-layer formation at high-latitudes following sudden commencement absorption events
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060242
This paper examines the formation of an enhanced E-layer that blankets the F-layer following sudden commencement absorption (SCA) events. Our case studies illustrate that storm sudden commencement (SSC) events cause impulsive precipitation of the otherwise trapped high energy electron population and that the precipitation of these high energy electrons may create considerable but short lived electron density enhancements (ionisation) at all ionospheric altitudes and particularly in the D and E layers (60-120 km altitude). The effect on HF communication links is demonstrated.Beacon-assisted quick determination of skywave propagation modes
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060274
Determining the propagation modes of high-frequency radar ray within the ionosphere and extracting their corresponding information quickly are quite important for over-the-horizon radar system. In general, the diagnosis to the ionosphere is implemented with special equipments. The equipments, often called ionosondes, have a capability of sounding over the full HF band and the whole illumination area at the price of complexity and time-consuming. When the ionosphere is disturbed drastically, error to estimate ionospheric parameters by ionosondes would be somewhat larger as a result of long processing time. In this paper, a technique for skywave propagation mode determination and parameter estimation has been proposed. Signal transmitted by radar and received by beacons has been used for estimation in the proposed method. The analysis for the dataset collected from an experiment in a short link (~700 km) show that the presented algorithm can offer some ionospheric information quickly, which would be helpful to improve accuracy of tracking and coordinate registration.Evaluation of the IRI model efficiency for operational forecast of HF propagation conditions
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060279
New approaches for adaptation of the international reference ionosphere model IRI to current ionospheric parameters are used to improve the determination of maximum usable frequency was given. MUF and path length D for HF waves propagated via the ionosphere with an example of one European path. Parameters foF2 (maximum frequency of the F2 layer) and TEC (total electron content) are used as adaptive ones. In additional the analytical approximation is proposed for the IRI model residual error. Its influence on MUF and D errors is given.Modelling of returned trajectories at heights below the maximum of the F2 layer
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060283
Radiosounding experiments aboard the "Mir" manned space station resulted in ionograms with retarded lower traces (RLT) (N.P. Danilkin, 2001). These unique traces can be explained as traces of trajectories which are irradiated from a satellite and after an inclined reflection from Earth come back to the satellite as a result of their sharp deviation by the irregularity in the ionosphere (returned trajectories). These trajectories require detailed research, which can be achieved by means of mathematical modeling. By varying positions of the satellite and the irregularity, it is possible to define optimal conditions of getting such trajectories in process of transionospheric radiosounding. The results of such an analysis are presented in the paper. Haselgrove method of ray tracing, also known as the method of characteristics was used (J. Haselgrove, 1955). The characteristic differential equations were handled by the method of Runge-Kutte. The detailed classification of calculated returned trajectories is presented in the paper, the dependence of each trajectory type on the position of the satellite and irregularity relative to each other and relative to the maximum of the F2 layer is shown.Inverse problems of ionospheric radiosounding at heights below the maximum of the F2 layer
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060277
The Tikhonov method of mathematical modelling is suggested for the solution of inverse problems of transionospheric radiosounding at heights below the maximum of the F2 layer and in cases of retarded lower traces (RLT).Variations in direction of arrival of HF signals propagating over a high latitude path under quiet and disturbed geomagnetic conditions
http://dl-live.theiet.org/content/conferences/10.1049/cp_20030450
A new network of transmitters and receivers has been installed in northern Scandinavia (including Svalbard), capable of measuring the time delay and Doppler spread characteristics and the directional structure of received signals on three HF paths. Based on the large amount of data expected from this experiment, a statistical classification of signal directional characteristics under various geophysical conditions and for all seasons can be made. In this paper, cases of both quiet and disturbed geomagnetic conditions have been studied, and comparisons have been made with data from magnetic disturbance observatories in the same geographic region.Models of HF spectral occupancy over a sunspot cycle
http://dl-live.theiet.org/content/conferences/10.1049/cp_20030420
A long-term joint UK-Swedish-German project on the measurement and analysis of HF spectral occupancy has been undertaken. This has resulted in an extensive database of spectral occupancy measurements made at four sites in northern Europe, over a complete sunspot cycle. Mathematical models for spectral occupancy have been developed to enable the estimation of future occupancy values. The procedures for measuring and modelling HF spectral occupancy are presented, with final occupancy models for northern Europe, corresponding to stable day and stable night ionospheric conditions.The simulation of HF off-great circle propagation effects due to large scale electron density structures within the polar cap and due to the mid-latitude trough
http://dl-live.theiet.org/content/conferences/10.1049/cp_20030465
Observations over recent years have established that large scale electron density structures are a common feature of the polar cap F-region ionosphere. Whilst experimental work has produced many useful results (Warrington, E.M. et al., IEE Proc. on Microwaves, Antennas and Propag., vol.144, p.241-9, 1997; Rogers, N.C. et al., IEE Proc. on Microwaves, Antennas and Propag., 2003; vol.144, p.91-6, 1997), they were obtained for a small number of paths and frequencies. In order to be able to develop tools to enable such effects to be considered in the design and operation of HF radio systems for which the signals impinge on the polar cap ionosphere, but for frequencies and paths not subject to experimental investigation, a ray tracing model has been developed. The results obtained from the ray tracing simulations are presented together with examples of experimental observations. However, it is well known that the high latitude ionosphere is an extremely complex HF propagation environment and, therefore, precise agreement between experiment and simulation has not been attempted and should not be expected.Effects of the upper atmosphere on terrestrial and Earth-space communications
http://dl-live.theiet.org/content/conferences/10.1049/cp_20030138
COST (cooperation in the field of scientific and technical research) is a framework for scientific and technical cooperation which facilitates the coordination of national research on a European level, and is concerned with basic and precompetitive studies as well as activities of public utility. Earth-satellite radiowave communications are central to many new radio services which are designed to meet increasing communications requirements. The proper understanding of the influence of the upper atmosphere on radiowave propagation is therefore essential to support the design, implementation and operation of many modem communication systems. The main objective of the COST 271 Action, entitled "Effects of the Upper Atmosphere on Terrestrial and Earth-Space Communications" (EACOS), is to promote, stimulate and coordinate European research in ionospheric and plasmaspheric areas. The work of the Action under four working groups is described and current results presented.The simulation of off-great circle HF propagation effects
http://dl-live.theiet.org/content/conferences/10.1049/cp_20030033
Observations over recent years have established that large scale electron density structures are a common feature of the polar cap F-region ionosphere. These structures take the form of convecting patches and arcs of enhanced electron density which form tilted reflection surfaces for HF radiowaves, allowing off great circle propagation paths to be established. Numerical ray tracing has been employed to simulate the effects of these structures on the ray paths of the radiowaves. The simulations have reproduced the precise character of experimental observations of the direction of arrival over a propagation path within the polar cap and of oblique ionograms obtained over the same path.HF propagation in tropical region; Nigerian airspace, a case study
http://dl-live.theiet.org/content/conferences/10.1049/cp_20030448
The purpose of this technical paper is to make an analysis of the propagation of HF radio signals in a tropical region. The propagation of HF radio signals through the ionosphere is used widely in Nigeria, most especially within airports in Nigeria. This paper surveys and highlights the problems experienced by the HF radio signal in its journey through the special ionosphere of a tropical region.Observations of Doppler spread, time-of-flight and direction of arrival of HF radio signals on a path affected by the mid-latitude trough
http://dl-live.theiet.org/content/conferences/10.1049/cp_20030441
Measurements of the time-of-flight and direction of arrival are presented for an HF radio signal on a subauroral path between Sweden and the UK. During the day, the signal usually arrives from the great circle path (GCP) direction. However, at night, especially during winter and equinoctial months, the signal often arrives at azimuths displaced from GCP. To the north, signals are probably scattered from irregularities in the trough wall.A simple polarisation fading model for HF propagation in the ionosphere
http://dl-live.theiet.org/content/conferences/10.1049/cp_20030443
A method of ray tracing to investigate the effects of Faraday rotation in the ionosphere is presented in the current paper. By applying analytical ray tracing, a polarisation fading model is developed for the HF signal propagating in a simple ionosphere. The scale of the ionospheric inhomogeneities being considered is large compared to the wavelength of the signal so that GO approximation remains applicable. Details on development of the model, results of the calculation and the effects of Faraday rotation on the signal are presented in subsequent sections. A comparison between the results ascertained from the simple model and a full 3D ray tracing package is included to verify the validity of the model.Measurements of the delay, Doppler and directional characteristics of obliquely propagating HF signals over several northerly paths and a comparison with vertical ionosonde and HF radar observations
http://dl-live.theiet.org/content/conferences/10.1049/cp_20030449
The high latitude ionosphere is a very dynamic and disturbed region containing irregularities which, on scales much greater than a wavelength, may be considered as providing a rough reflecting surface for obliquely propagating HF radiowaves. To improve our knowledge and understanding of the complex propagation mechanisms prevalent in the high latitude region, an experimental campaign is currently being conducted with a receiver system capable of measuring the delay and Doppler spread characteristics and the directional structure of the received signals at Kiruna in northern Sweden.