A5062665328- Ionosphere and magnetosphere dynamics
- GNSS positioning and interference
- Earthquake Detection and Analysis
- Atmospheric aerosols and clouds
- Meteorological Phenomena and Simulations
- Geophysics and Gravity Measurements
- Oceanographic and Atmospheric Processes
- Soil Moisture and Remote Sensing
- Ocean Waves and Remote Sensing
- Radio Wave Propagation Studies
- Solar and Space Plasma Dynamics
- Precipitation Measurement and Analysis
- Climate variability and models
- Lightning and Electromagnetic Phenomena
- Atmospheric chemistry and aerosols
- Geology and Paleoclimatology Research
- Underwater Acoustics Research
- Seismic Waves and Analysis
- Atmospheric and Environmental Gas Dynamics
- Remote Sensing in Agriculture
- Aeolian processes and effects
- Radioactivity and Radon Measurements
- Soil Geostatistics and Mapping
- Geomagnetism and Paleomagnetism Studies
- Electromagnetic Compatibility and Measurements
University of Bath
2009-2024
Designability
2015
University of Reading
1997-2006
Aberystwyth University
1991-1997
University of Wales
1994-1997
Natural Environment Research Council
1997
Abstract. Results are presented of a study the temporal and spatial variability in meteor count rate observations from three VHF radars. These radar located Arctic (at Esrange, 68° N), Antarctic Rothera, S) near Equator (on Ascension Island, 8° S). It is found that for all locations there strong diurnal cycle observed hourly counts time maxima minima these depends on month year. In addition, at high latitude annual monthly-mean counts, whereas low semi-annual cycle. At also an mean height...
This paper presents the results from one of first observations ionospheric scintillation taken using Low-Frequency Array (LOFAR). The observation was strong natural radio source Cassiopeia A, overnight on 18–19 August 2013, and exhibited moderately scattering effects in dynamic spectra intensity received across an observing bandwidth 10–80 MHz. Delay-Doppler (the 2-D FFT spectrum) hour showed two discrete parabolic arcs, with a steep curvature other shallow, which can be used to provide...
Abstract Assimilation of salinity into ocean and climate general circulation models is a very important problem. Argo data now provide far more observations than ever before. In addition, good analysis over time in reanalyses can give results for understanding change. Here it shown from the historical database that large regions globe (mainly midlatitudes lower latitudes) variance on an isotherm S(T) often less measured at particular depth S(z). It also dominant temporal variations occur...
A variety of economic sectors rely upon the use Global Navigation Satellite Systems (GNSS) in areas such as autonomous navigation, timing, land management, oil exploration, precision agriculture, civil aviation. Spatial and temporal gradients (or irregularities) ionospheric plasma density distribution introduce disturbances on propagation GNSS radio signals. These originate additional errors outages that degrade positioning quality, thus producing an impact GNSS-based applications. The...
Observations with a 46.5‐MHz radar system at Aberystwyth, Wales (52°N, 4°W) over the period February 1990 to May 1994 have shown pronounced seasonal variation in height range of mesospheric echoes. These were observed 64–84 km all seasons, but those still greater heights confined summer months. Coordinated and lidar observations same site during 1993 that these intense echoes summer, analogous polar mesosphere (PMSE), are associated low mesopause temperatures; weaker winter seem be regions...
Cloud cover is conventionally estimated from satellite images as the observed fraction of cloudy pixels. Active instruments such radar and Lidar observe in narrow transects that sample only a small percentage area over which cloud estimated. As consequence, estimate has an associated sampling uncertainty, usually remains unspecified. This paper extends Bayesian method estimation, also provides analytical error. applied to test sensitivity this error characteristics, number variability...
The general probability distribution for the fractional amount of a geophysical parameter contained within finite transect has been published previously. On basis this information confidence intervals were placed on observed fraction prior to measurement from knowledge underlying distributions length regions and gaps between such regions. In form, hypothesis testing models these could be made given fraction. However, what is also required (for change detection, example) interval true Such...
The fractional water content of soil plays a central role in the complex interactions between Earth and its hydrological cycle. However, obtaining continuous measurements wide-area moisture is difficult. In our study, novel method for remote sensing explored that makes use variations time delay on Loran-C surface waves. An analysis was carried out using such signals recorded over three-week period at University Bath, U.K., from transmitting station Northern France. Model data European Centre...
Abstract Four primary plasma instability processes have been proposed in the literature to explain generation of phase scintillation associated with polar cap patches. These are gradient drift, current convective, and Kelvin‐Helmholtz instabilities a small‐scale “turbulence” process. In this paper range possible values linear growth rates for each these is explored using Dynamics Explorer 2 satellite observations. It found that inertial turbulence dominant process, followed by collisional...
A model is developed of the gradient drift instability growth rate in north polar cap ionosphere, utilizing a novel approach employing an ionospheric imaging algorithm. The values calculated by this are turn used to estimate how amplitudes actual waves vary over time as plasma drifts and rates change with time. Ionospheric again order determine velocities. final output from assess linear correlation between scintillation indices S 4 σ recorded several GPS L1 band receivers stationed mean...
Around fifty LORAN (LOng RAnge Navigation) transmitters in the northern hemisphere currently launch continuously pulsed 100 kHz radio waves into Earth's atmosphere for marine navigation. It is discovered that from transmissions can be detected by DEMETER satellite at an altitude of ∼660 km above transmitters. These novel electric field measurements space enable determination nocturnal transionospheric attenuation comparison with ground based measurements. The on indicate equivalent to a...
Abstract The array analyses used for seismic and infrasound research are adapted applied here to the electromagnetic radiation from radio transmitters submarine communication. It is found that analysis enables a determination of slowness arrival azimuth wave number vectors associated with radiation. measurements ∼20–24 kHz waves communication an 10 receivers distributed over area ∼1 km ×1 km. observed range ∼2.7 ns/m ∼4.1 ns/m, deviations between expected azimuths ∼−9.7° ∼14.5°. experimental...
Abstract The Earth's natural electromagnetic environment is disturbed by anthropogenic noise. Here we report the first results from an noise survey of sky. locations sources are mapped on hemisphere above a distributed array wideband receivers that operate in small aperture configuration. It found can be localized at elevation angles up to ∼60° sky, well horizon. sky also exhibits zones with little or no toward local zenith and southwest array. These obtained rigorous analysis residuals...
Stringent accuracy requirements need to be met for eLoran deployment in marine navigation and harbour entrance approach. A good model is therefore required predict the positioning at user's receiver locations. Accuracy depends on variations of additional secondary factors (ASFs) primary factor delay. The changes air refractive index caused (PF) delay signal, current models do not take this into account. This paper proposes an improved empirical that considers contributions air, often...
A model is presented of the growth rate turbulently generated irregularities in electron concentration northern polar cap plasma patches. The turbulence by short‐term fluctuations electric field imposed on ionosphere mapping from magnetosphere. uses an ionospheric imaging algorithm to specify state throughout. rates are used estimate mean amplitudes for irregularities, and these compared with observations scintillation indices S 4 σ ϕ calculating linear correlation coefficients between them....
Abstract The low‐frequency radio sky shows the locations of electromagnetic sources with a characteristic dilution precision. Here we report thorough high‐resolution analysis waves from (∼20–150 kHz) communication transmitters which are recorded small aperture array receivers during day. It is found that observed precision results geometry receivers, birefringent wave propagation, and correlated multipath propagation waves. influence on reduced by taking into account impulse response array....
The distribution of the total length a geophysical parameter along finite linear transect is required to determine confidence intervals for its true mean fractional coverage. analogous time queue busy within interval. As posed as queuing problem, this has been subject study last 40 years using variety approaches. Using heuristic approach, general equation derived context. an example, applied exponential field and validated against published simulation leads in ice floes. formalism allows...
In a large number of satellite infrared images the proportion randomly spaced intervals length p pixels (width, one pixel) that are registered as completely cloudy falls exponentially with increasing interval length. This is exactly to be expected for one-dimensional exponential cloud field. Further, rectangular there also an falloff, size rectangle increases, in intervals. However, rate falloff dependent on perimeter rather than its area. It suggested this can explained if and width clouds...
Abstract The cloud overlap weighting parameter, α, relates the averaged combined fraction between two altitude levels to averages derived under random and maximum assumptions. In several recent studies, it is found that α decreases approximately exponentially with separation distance altitudes. This note provides a mathematical basis for these observed behaviours. An analytic expression derived. It solely function of cross‐correlation fractions at altitudes, individual variances in Only...
Abstract. Comparisons are made between horizontal wind measurements carried out using a VHF-radar system at Aberystwyth (52.4°N, 4.1°W) and radiosondes launched from Aberporth, some 50 km to the south-west. The radar results derived Doppler zenith angles of 6° in two orthogonal planes vertical direction. Measurements on total 398 days over 2-year period considered, but major part study involves statistical analysis data collected during 75 radiosonde flights selected minimise spatial...
eLoran needs to satisfy the user requirements for accuracy, availability, continuity and integrity fulfil its envisioned role as a backup system GPS. The accuracy performance at receiver locations is dependent on variations of Additional Secondary Factor caused by changes in ground conductivity. This paper focuses analysis maritime harbour entrance approach. Based observational ASF data, new, updated more accurate empirical model time arrival variance that improves upon existing models...