Paul started his career at the University of Southampton (1977 - 81) where he discovered and explained a new non-linear demodulation effect (of LF broadcast transmissions) in the high latitude ionosphere partly using equipment that he had developed. He described how coherent modulation from a number of transmitters can preferentially modify the ionosphere in specific locations. This work was most recently cited 2021.
During this time, he also conducted a small study on ELF Schumann resonance signals during a sudden ionospheric disturbance and compared the results with theory.
After a short period working in the satellite communications industry, Paul was appointed to the Ministry of Defence (MOD), Royal Aircraft Establishment where he was rapidly promoted and offered a “fast track” career in London. He declined this opportunity preferring a research career.
His early work (1981 – 1990) on meteor burst communications (MBC) identified a hitherto and important signal loss mechanism, due to signal polarisation rotation in the ionosphere and this significantly enhanced the accuracy of the MBC models. This paper was last cited in 2017.
A review paper was well received and later work on the use of phased arrays, facilitated MBC systems operating with significantly enhanced data rates. Recently (2021), the UK MOD reinitiated a MBC programme which draws on this early work.
In 1989 Paul worked on sabbatical at the University of Massachusetts, Lowell in the USA. Here he explored the feasibility of using advanced ionosondes to measure high-latitude ionospheric convection, identifying the technique’s strengths and weaknesses. This work demonstrated that for Bz south the convection pattern was well represented by a two-cell Heppner and Maynard model and notably agreed well with satellite measurements. When Bz was north, the convection pattern was much more variable and was best represented by a four-cell model.
Back in the UK (1990 - 2000) his theoretical focus was on the development of fast analytic (rather than numerical) ray tracing techniques which could be used on the relatively slow computers at that time. This work was novel because not only did it provide for double differential altitude functions, but it accommodated longitudinal gradients.
A further theoretical research theme at this time, explored the use of non-linear dynamical modelling to forecast the ionosphere over different timescales. This work used radial basis functions which facilitated optimisation without the risk of finding a local minimum. The work also developed an approach to interpolate missing points in data series, based on minimising the data entropy.
During this period a new oblique ionosonde, ROSE was developed which was operationally used by the UK Ministry of Defence (MOD). ROSE was later developed further to support scientific research. This ionosonde exhibited much higher range and frequency resolution than many vertical ionosondes which was necessary to invert the ionogram and derive the electron density profile.
Of particular note in this period was Paul’s leadership of the pioneering international DAMSON programme (1993-2000) to measure and understand the HF communications propagation channel. This work, carried out by a team from Sweden, Norway, Canada and the UK, was undertaken in cooperation with major communications modem manufacturers. NATO’s robust HF modems are based on the results of this work.
In the early 2000’s Paul considered the consequence of ionospheric contraction due to increased levels of CO2 in the atmosphere, noting that at high altitudes increases in CO2 cause increased radiation of heat into space. Two papers suggest that the ionosphere in northern Norway is indeed contracting and that this will have a consequence on models of the ionosphere and particularly HF communication signal coverage.
Between 2000 and 2010 Paul focused on the measurement of the time and frequency coherence of the UHF trans-ionospheric channel which is degraded by small scale irregularities. To do this he used the ALTAIR space track radar on Kwajalein Atoll in the Pacific. This led to the first open literature report of these parameters, which were needed to support the design of both UHF space-based surveillance radars and modems for the MUOS satellite constellation.
Theoretical support was provided by team development of a phase screen model to predict the scintillation. This model was successfully able to reproduce many of the experimental results.
The ALTAIR measurements and supporting theoretical work were partly driven by a UK interest to fly a low frequency (400 MHz) space-based radar and a number of papers during this period and later explored these issues. GPS and satellite radio beacon satellite signals were used to evaluate the spatial decorrelation of signals and the consequences for a space radar.
This was also the period during which Paul’s team started the development of assimilative ionospheric models which combine data with a background model to generate a best estimate of the ionospheric electron density. Such models can, for example, be combined with accurate ray tracing to estimate and predict the performance of communication and radar systems.
Between 2010 and 2013, Paul led the UK team, working in collaboration with the USA, to explore whether beneficial artificial layers and disruptive irregularities could be formed by the deposition of chemicals into the ionosphere. This involved the development of a direction finding ionosonde and the launching of rockets, with an apogee of ~200 km, into the ionosphere. A classified joint UK-US programme still continues. Two journal papers were published.
In 2013 Paul joined the University of Birmingham, where he continued research, first started 5-years before, on the impact of the ionosphere on space-radars. Amongst other innovations, this led to two new techniques to map the equatorial ionospheric turbulence using synthetic aperture radars.
In 2018 Paul renewed his interest in Over the Horizon Radar Systems (OTHRs) and conceived a new architecture. This architecture exchanges the conventional relatively short transmit antenna array and long receive array for a long transmit array and a short receive array. This has many advantages including that of making the receivers relocatable. A patent was applied for in 2019 and since 2020 the technique has been successfully explored, with the added benefit of developing the UK’s first OTHR propagation and system model.
In 2020 Paul successfully won, as co-investigator, two of the UK Space Weather Instrumentation, Measurement, Modelling and Risk (SWIMMR) projects. Within these projects his main interests are the development of ionospheric scintillation forecasting techniques.
In 2022, Paul re-examined the characteristics of the wideband trans-ionospheric propagation channel using signals from the MUOS satellite in geosynchronous orbit, especially for communication systems. This work demonstrated that flat fading dominates over frequency selective fading for all operating bandwidths up to 15 MHz.