Comparisons are made between horizontal wind measurements carried out using a VHF-radar system at Aberystwyth (52.4Â°N, 4.1Â°W) and radiosondes launched from Aberporth, some 50 km to the south-west. The radar wind results are derived from Doppler wind measurements at zenith angles of 6Â° in two orthogonal planes and in the vertical direction. Measurements on a total of 398 days over a 2-year period are considered, but the major part of the study involves a statistical analysis of data collected during 75 radiosonde flights selected to minimise the spatial separation of the two sets of measurements. Whereas good agreement is found between the two sets of wind direction, radar-derived wind speeds show underestimates of 4â6% compared with radiosonde values over the height range 4â14 km. Studies of the characteristics of this discrepancy in wind speeds have concentrated on its directional dependence, the effects of the spatial separation of the two sets of measurements, and the influence of any uncertainty in the radar measurements of vertical velocities. The aspect sensitivity of radar echoes has previously been suggested as a cause of underestimates of wind speeds by VHF radar. The present statistical treatment and case-studies show that an appropriate correction can be applied using estimates of the effective radar beam angle derived from a comparison of echo powers at zenith angles of 4.2Â° and 8.5Â°.

Zenith

Wind profiler

10.1007/s005850050499

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Making ODR Human

International Journal of Online Dispute Resolution (2018)

L. Thomas Sarah Kaur Simon Goodrich

10.5553/ijodr/235250022018005102013

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Night-to-night changes in the characteristics of gravity waves at stratospheric and lower-mesospheric heights

Annales Geophysicae (1998)

Adrian McDonald L. Thomas D. P. Wareing

Abstract. Observations made with the co-located Rayleigh lidar and MST radar systems at Aberystwyth (52.4°N, 4.1°W) in Wales and radiosondes from Valentia (51.9°N, 10.2°W) in Eire are used to investigate the changes in the vertical propagation of gravity waves during periods of 4 days in June 1995 and February 1993. In each month, the lidar observations show that the wave activity in the upper stratosphere and lower mesosphere changes between two pairs of days. The radar and radiosonde measurements indicate that mountain waves make no contribution to the changes in intensity. Instead, the changes seem to arise largely from the presence or absence of long-period waves with vertical wavelengths near 8 and 10 km in June and February, respectively. The influence of such waves on the vertical wavenumber spectra is examined and related to the evidence for convective instabilities provided by the temperature profiles.

Key words. Rayleigh lidar · MST radar systems · Radiosondes · Gravity waves

10.1007/s005850050596

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Tool integration: experiences from the BOOST project

Robert J. Gautier Chris Loftus Edel Sherratt L. Thomas

The BOOST project aims to support the development of telecommunications services by establishing effective ways of creating object-oriented service creation environments (SCEs). A major part of the project has entailed the constructing SCEs by integrating existing software tools. This paper evaluates different approaches to tool integration, covering both integration by encapsulation within an existing environment, and direct tool-to-tool integration. The use of Tcl, a language to increase tool programmability, is discussed, and examples illustrating its application in BOOST are provided. Finally, a general mechanism for direct tool-to-tool integration, and an approach towards fully open, active environments and services are presented.< >

System Integration

10.1109/see.1995.393619

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The small-scale structure of VHF mesospheric summer echo layers observed at mid-latitudes

Annales Geophysicae (1997)

David A Hooper L. Thomas

The VHF radar system at Aberystwyth (52.4° N, 4.1°E) has been used to make high-time-resolution, multi-beam observations of mesospheric summer echo layers. These show that the altitude and the sense of vertical movement of the layers can vary over time-scales of minutes and horizontal scales of kilometres. In general, the altitude profiles of signal-to-noise ratio provide evidence of a bifurcated structure with sharp changes in the horizontal wind vector and vertical velocity, and enhanced spectral width occurring at the bifurcation level. The implications of the small-scale structure for studies of the aspect sensitivity of radar returns are discussed, and the changes in wind-field at the bifurcation level are compared with 'wind corners' observed in rocket studies of the mesosphere at polar latitudes.

10.1007/s005850050522

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Pruning of the transform space in block-based fractal image compression

IEEE International Conference on Acoustics Speech and Signal Processing (1993)

L. Thomas Farzin Deravi

A method for fractal image compression is presented which is an extension of A.E. Jacquin's (1990) algorithm. The proposed algorithm improves Jacquin's block-based algorithm by allowing irregularly shaped fractal transformations. The method for producing these transformations is to start with the block-based approach and then prune the transformations in the transform space. The results show a large improvement in compression ratio over Jacquin's system at the same signal-to-noise ratio. For high compression ratios the system has similar performance to the JPEG (Joint Photographic Experts Group) standard.< >

Fractal compression

Pruning

Fractal transform

JPEG

10.1109/icassp.1993.319817

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Deep Visual Place Recognition for Waterborne Domains

2022 IEEE International Conference on Image Processing (ICIP) (2022)

L. Thomas Michael Edwards Austin Capsey Alma Rahat Matt Roach

Image based place recognition has achieved state of the art performance on terrestrial image datasets, however there is very little publicly available research on how these systems perform on waterborne imagery in order to carry out place recognition for autonomous sea vessels. This domain may provide new visual challenges such as water obstruction, distance from shore, lower atmospheric visibility, and camera stability. In this paper, we compare performance and saliency of state of the art place recognition on both terrestrial imagery and waterborne imagery from the Symphony Lake dataset, to see how capable modern pipelines are at adapting to the latter. We utilize convolutional neural network features to highlight salient regions of the candidate image that contributed to its retrieval to gain further insight into what key features are being extracted for each.

Visibility

10.1109/icip46576.2022.9897962

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Improving motivation and performance through personal development in large introductory software engineering courses

Mark B. Ratcliffe John Woodbury L. Thomas

In 1993, the first year class in the Department of Computer Science at the University of Wales, Aberystwyth totalled just 93 students. This year it is 190. In line with most universities in the UK the total number of students in the department has more than doubled in the last five years and as is typical, the number of staff is largely unchanged. This paper describes two main development phases that have been undertaken to enhance the student experience and improve the quality of our teaching despite the ever-increasing workload.

10.1109/csee.2002.995203

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Citations (11)