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Papers by Michael Warrington
2020 21st International Radar Symposium (IRS), 2020
High frequency Over-the-Horizon Radar (OTHR) provides an economical means to track non-cooperativ... more High frequency Over-the-Horizon Radar (OTHR) provides an economical means to track non-cooperative air targets over large expanses of land and ocean. Because of dynamic ionospheric conditions in polar regions, any OTHR would necessitate a system where the operating frequencies and elevation angles change periodically to maintain constant detection of targets downrange. In this regard, an accurate electron density model is necessary for the purpose of improving operational OTHR and OTHR planning/design. 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 effect of frequency monitoring system for OTHR due to the presence of patches of enhanced electron density within the polar cap ionosphere has been studied in this paper.
Annals of Geophysics, 2009
Different applications of radio systems are based on the implementation of antenna arrays. Classi... more Different applications of radio systems are based on the implementation of antenna arrays. Classically, radio direction finding operates with a multi channel receiving system connected to an array of receiving antennas. More recently, MIMO architectures have been proposed to increase the capacity of radio links by the use of antenna arrays at both the transmitter and receiver. The first part of this paper describes some novel experimental work carried out to examine the feasibility of applying MIMO techniques for communications within the HF radio band. A detailed correlation analysis of a variety of different antenna array configurations is presented. The second section of the paper also deals with HF MIMO communications, focusing on the problem from a modelling point of view. The third part presents a sensitivity analysis of different antenna array structures for HF direction finding applications. The results demonstrate that when modelling errors, heterogeneous antenna arrays are more robust in comparison to homogeneous structures.
Researchers at the University of Leicester, Lancaster University and St Petersburg State Universi... more Researchers at the University of Leicester, Lancaster University and St Petersburg State University have developed various models that can be employed in HF radio propagation predictions. Signal coverage predictions make use of numerical ray tracing to estimate the ray paths through a model ionosphere that includes various ionospheric features prevalent at high latitudes (in particular patches, arcs, ionisation tongue, auroral zone irregularities and the mid-latitude trough). Modelling of D-region absorption is also included. GOES satellites provide information on X-ray flux (causing shortwave fadeout during solar flares) and precipitating energetic proton flux which correlates strongly with Polar Cap Absorption (PCA). Solar wind and interplanetary magnetic field measurements from the ACE or DSCOVR spacecraft provide geomagnetic index estimates used to model the location of both auroral absorption and the proton rigidity cutoff boundary that defines the latitudinal extent of PCA dur...
Commercial airlines began operations over polar routes in 1999 with a small number of proving fli... more Commercial airlines began operations over polar routes in 1999 with a small number of proving flights. By 2014 the number had increased to in excess of 12,000 flights per year, and further increases are expected. For safe operations, the aircraft have to be able to communicate with air traffic control centres at all times. This is achieved by VHF links whilst within range of the widespread network of ground stations, and is by HF radio in remote areas such as the Polar regions, the North Atlantic and Pacific where VHF ground infrastructure does not exist. Furthermore, the Russian side of the pole only has HF capability. Researchers at the University of Leicester and at Lancaster University have developed various models (outlined below) that can be employed in HF radio propagation predictions. It is anticipated that these models will form the basis of an HF forecasting and nowcasting service for the airline industry. Propagation coverage predictions make use of numerical ray tracing ...
It is well known that the auroral zone ionosphere contains steep time varying gradients in electr... more It is well known that the auroral zone ionosphere contains steep time varying gradients in electron density which can produce large off-great circle bearings in the direction of arrival of HF radio signals reflected from this region of the ionosphere. Recent DF measurements at a high latitude site indicate that large bearing errors are also observed in signals reflected from
IEE Proceedings - Microwaves, Antennas and Propagation, 1995
From measurements of the amplitude and phase of ionospherically propagated H F radio signals rece... more From measurements of the amplitude and phase of ionospherically propagated H F radio signals received at several spaced antennas, the direction of arrival of the signals in both azimuth and elevation can be determined. A series of measurements has been undertaken using a wide aperture antenna array on signals received from several European broadcast stations at distances of up to about 1400 km, and the directions of arrival estimated by means of two superresolution algorithms; MUSIC and an iterative null steering method (an approximate maximum likelihood estimator) based on the IMP and DOSE algorithms. A detailed comparison of the performance of the two algorithms has been undertaken, and it is concluded that the null steering algorithm is significantly better than MUSIC at resolving the various propagation modes, particularly for short signal analysis periods. Paper 1829H (Ell), first received 4th August and in revised form 16th
Low frequency (30-300 kHz) radio waves can propagate to great distances with little attenuation i... more Low frequency (30-300 kHz) radio waves can propagate to great distances with little attenuation in the cavity formed by the earth and the ionosphere. Because of the relatively high frequency at LF, many active propagation modes can occur between the transmitter and receiver. Changes in the ionospheric conductivity or reflection height can influence the phase and amplitude of these modes and, hence, produce mutual interference. Because of these interference effects, the propagation is less stable than at VLF and the received field strength becomes more difficult to predict. In the present investigation, the WAVEHOP program was employed in conjunction with a range of ionospheric models to estimate the receiver field strength over a number of experimental paths. The predicted values were compared with those measured in an attempt to validate the ionospheric models and the method of calculation.
IEE Proceedings - Microwaves, Antennas and Propagation, 2000
kidio WRVCS a1 fi-cilucncics less tliiin nrotind 100 kl IZ can propagite to p i l l dislanccs wit... more kidio WRVCS a1 fi-cilucncics less tliiin nrotind 100 kl IZ can propagite to p i l l dislanccs with little uttenu;iticsn in llic cavity l'orincd by the earth and tlic ioiiosplicre. At tlicsc rrcqucncies, nitlily active propitgation niodcs c:in occiii' bctwan the transmillcr ancl rcceiver. Clxirigs in thc ionospheric conductivity or rcflcction height i nlluciice the relative pliascs aiid miplitudcs a[ tlic propagating inodcs :ind hence Ihcir vcctor sutn. Tlic pi-opagation is less siahlc at LF than :II VLF ; a d thc icccivcd ficld strcngth is moic difficult to predict. In this investigation, 1lic Wriveliop prograin has hccu cinplopd i n conj tunclion with previously irnpublisheci suniincr-tiinc ioiiosplieric: modcls LO cstiinalc thc rcceivcci licld strcrigth over ii iiumhcr of experimcnlal paths. The predictd viilucs havc been compared with h c Incasuretnents l o validalc the ionosphcric modcls mil the inclhod of calculation.
Aircraft operating on trans-polar routes require reliable HF (3-30 MHz) radio communications link... more Aircraft operating on trans-polar routes require reliable HF (3-30 MHz) radio communications links to be maintained throughout each flight. However, solar flares and interplanetary coronal mass ejections (ICME) can often result in enhancements of the electron density in the Earth’s ionosphere, which can strongly attenuate HF radio waves in the Polar Regions. In some cases this can result in the cancellation or diversion of flights for periods of several days. This paper describes the scientific basis for an online service for airlines that predicts HF radio coverage for polar flight routes by combining nowcast maps of HF absorption in the lower (D-region) ionosphere with ray-tracing radio propagation algorithms. The absorption maps are generated by assimilating real-time measurements of cosmic radio noise absorption from 25 ‘relative ionospheric opacity meters’ (riometers) deployed across Canada and Scandinavia. These data are combined with real-time X-ray flux and energetic (1-100 ...
2020 21st International Radar Symposium (IRS), 2020
High frequency Over-the-Horizon Radar (OTHR) provides an economical means to track non-cooperativ... more High frequency Over-the-Horizon Radar (OTHR) provides an economical means to track non-cooperative air targets over large expanses of land and ocean. Because of dynamic ionospheric conditions in polar regions, any OTHR would necessitate a system where the operating frequencies and elevation angles change periodically to maintain constant detection of targets downrange. In this regard, an accurate electron density model is necessary for the purpose of improving operational OTHR and OTHR planning/design. 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 effect of frequency monitoring system for OTHR due to the presence of patches of enhanced electron density within the polar cap ionosphere has been studied in this paper.
Annals of Geophysics, 2009
Different applications of radio systems are based on the implementation of antenna arrays. Classi... more Different applications of radio systems are based on the implementation of antenna arrays. Classically, radio direction finding operates with a multi channel receiving system connected to an array of receiving antennas. More recently, MIMO architectures have been proposed to increase the capacity of radio links by the use of antenna arrays at both the transmitter and receiver. The first part of this paper describes some novel experimental work carried out to examine the feasibility of applying MIMO techniques for communications within the HF radio band. A detailed correlation analysis of a variety of different antenna array configurations is presented. The second section of the paper also deals with HF MIMO communications, focusing on the problem from a modelling point of view. The third part presents a sensitivity analysis of different antenna array structures for HF direction finding applications. The results demonstrate that when modelling errors, heterogeneous antenna arrays are more robust in comparison to homogeneous structures.
Researchers at the University of Leicester, Lancaster University and St Petersburg State Universi... more Researchers at the University of Leicester, Lancaster University and St Petersburg State University have developed various models that can be employed in HF radio propagation predictions. Signal coverage predictions make use of numerical ray tracing to estimate the ray paths through a model ionosphere that includes various ionospheric features prevalent at high latitudes (in particular patches, arcs, ionisation tongue, auroral zone irregularities and the mid-latitude trough). Modelling of D-region absorption is also included. GOES satellites provide information on X-ray flux (causing shortwave fadeout during solar flares) and precipitating energetic proton flux which correlates strongly with Polar Cap Absorption (PCA). Solar wind and interplanetary magnetic field measurements from the ACE or DSCOVR spacecraft provide geomagnetic index estimates used to model the location of both auroral absorption and the proton rigidity cutoff boundary that defines the latitudinal extent of PCA dur...
Commercial airlines began operations over polar routes in 1999 with a small number of proving fli... more Commercial airlines began operations over polar routes in 1999 with a small number of proving flights. By 2014 the number had increased to in excess of 12,000 flights per year, and further increases are expected. For safe operations, the aircraft have to be able to communicate with air traffic control centres at all times. This is achieved by VHF links whilst within range of the widespread network of ground stations, and is by HF radio in remote areas such as the Polar regions, the North Atlantic and Pacific where VHF ground infrastructure does not exist. Furthermore, the Russian side of the pole only has HF capability. Researchers at the University of Leicester and at Lancaster University have developed various models (outlined below) that can be employed in HF radio propagation predictions. It is anticipated that these models will form the basis of an HF forecasting and nowcasting service for the airline industry. Propagation coverage predictions make use of numerical ray tracing ...
It is well known that the auroral zone ionosphere contains steep time varying gradients in electr... more It is well known that the auroral zone ionosphere contains steep time varying gradients in electron density which can produce large off-great circle bearings in the direction of arrival of HF radio signals reflected from this region of the ionosphere. Recent DF measurements at a high latitude site indicate that large bearing errors are also observed in signals reflected from
IEE Proceedings - Microwaves, Antennas and Propagation, 1995
From measurements of the amplitude and phase of ionospherically propagated H F radio signals rece... more From measurements of the amplitude and phase of ionospherically propagated H F radio signals received at several spaced antennas, the direction of arrival of the signals in both azimuth and elevation can be determined. A series of measurements has been undertaken using a wide aperture antenna array on signals received from several European broadcast stations at distances of up to about 1400 km, and the directions of arrival estimated by means of two superresolution algorithms; MUSIC and an iterative null steering method (an approximate maximum likelihood estimator) based on the IMP and DOSE algorithms. A detailed comparison of the performance of the two algorithms has been undertaken, and it is concluded that the null steering algorithm is significantly better than MUSIC at resolving the various propagation modes, particularly for short signal analysis periods. Paper 1829H (Ell), first received 4th August and in revised form 16th
Low frequency (30-300 kHz) radio waves can propagate to great distances with little attenuation i... more Low frequency (30-300 kHz) radio waves can propagate to great distances with little attenuation in the cavity formed by the earth and the ionosphere. Because of the relatively high frequency at LF, many active propagation modes can occur between the transmitter and receiver. Changes in the ionospheric conductivity or reflection height can influence the phase and amplitude of these modes and, hence, produce mutual interference. Because of these interference effects, the propagation is less stable than at VLF and the received field strength becomes more difficult to predict. In the present investigation, the WAVEHOP program was employed in conjunction with a range of ionospheric models to estimate the receiver field strength over a number of experimental paths. The predicted values were compared with those measured in an attempt to validate the ionospheric models and the method of calculation.
IEE Proceedings - Microwaves, Antennas and Propagation, 2000
kidio WRVCS a1 fi-cilucncics less tliiin nrotind 100 kl IZ can propagite to p i l l dislanccs wit... more kidio WRVCS a1 fi-cilucncics less tliiin nrotind 100 kl IZ can propagite to p i l l dislanccs with little uttenu;iticsn in llic cavity l'orincd by the earth and tlic ioiiosplicre. At tlicsc rrcqucncies, nitlily active propitgation niodcs c:in occiii' bctwan the transmillcr ancl rcceiver. Clxirigs in thc ionospheric conductivity or rcflcction height i nlluciice the relative pliascs aiid miplitudcs a[ tlic propagating inodcs :ind hence Ihcir vcctor sutn. Tlic pi-opagation is less siahlc at LF than :II VLF ; a d thc icccivcd ficld strcngth is moic difficult to predict. In this investigation, 1lic Wriveliop prograin has hccu cinplopd i n conj tunclion with previously irnpublisheci suniincr-tiinc ioiiosplieric: modcls LO cstiinalc thc rcceivcci licld strcrigth over ii iiumhcr of experimcnlal paths. The predictd viilucs havc been compared with h c Incasuretnents l o validalc the ionosphcric modcls mil the inclhod of calculation.
Aircraft operating on trans-polar routes require reliable HF (3-30 MHz) radio communications link... more Aircraft operating on trans-polar routes require reliable HF (3-30 MHz) radio communications links to be maintained throughout each flight. However, solar flares and interplanetary coronal mass ejections (ICME) can often result in enhancements of the electron density in the Earth’s ionosphere, which can strongly attenuate HF radio waves in the Polar Regions. In some cases this can result in the cancellation or diversion of flights for periods of several days. This paper describes the scientific basis for an online service for airlines that predicts HF radio coverage for polar flight routes by combining nowcast maps of HF absorption in the lower (D-region) ionosphere with ray-tracing radio propagation algorithms. The absorption maps are generated by assimilating real-time measurements of cosmic radio noise absorption from 25 ‘relative ionospheric opacity meters’ (riometers) deployed across Canada and Scandinavia. These data are combined with real-time X-ray flux and energetic (1-100 ...