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S. J. Holgate, P. L. Woodworth, P. R. Foden, and J. Pugh

Abstract

This short note provides conclusions of a study of the various factors that determine the delay between tsunami arrival at a tide gauge station and data being made available at tsunami warning centers. The various delays involved include those associated with the tide gauge hardware and measurement methods and with the form of telemetry employed. It is shown that the most widely used form of telemetry in existing tsunami networks (meteorological satellite data collection platforms) can be improved upon significantly with the use of modern telemetry alternatives [notably Inmarsat’s Broadband Global Area Network (BGAN)], enabling faster, more frequent, more secure, and higher bandwidth transmissions of tide gauge data.

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M. A. Morales Maqueda, N. T. Penna, S. D. P. Williams, P. R. Foden, I. Martin, and J. Pugh

Abstract

A geodetic GPS receiver has been installed on a Wave Glider, an unmanned water surface vehicle. Using kinematic precise point positioning (PPP) GPS, which operates globally without directly requiring reference stations, surface heights are measured with ~0.05-m precision. The GPS Wave Glider was tested in Loch Ness, Scotland, by measuring the gradient of the loch’s surface height. The experiment took place under mild weather, with virtually no wind setup along the loch and a wave field made mostly of ripples and wavelets. Under these conditions, the loch’s surface height gradient should be approximately equal to the geoid slope. The PPP surface height gradient and that of the Earth Gravitational Model 2008 geoid heights do indeed agree on average along the loch (0.03 m km−1). Also detected are 1) ~0.05-m-sized height changes due to daily water pumping for hydroelectricity generation and 2) high-frequency (0.25–0.5 Hz) oscillations caused by surface waves. The PPP heights compare favorably (~0.02-m standard deviation) with relative carrier phase–based GPS processing. This suggests that GPS Wave Gliders have the potential to autonomously determine centimeter-precise water surface heights globally for lake modeling, and also for applications such as ocean modeling and geoid/mean dynamic topography determination, at least for benign surface states such as those encountered during the reported experiment.

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