THS in Scotland Evening Meeting

THS in Scotland
Date28 November 2018
Time18:30
VenueCarmelite Hotel, Stirling Street, AB11 6JU

The programme will feature the following presentations:

Earth based GNSS measurements of sea level: measuring tides without getting your feet wet
by Simon Williams, Geodetic Geophysicist, NOC Southampton

Global Navigation Satellite Systems (GNSS) have, over the last few decades, transformed positioning, navigation and timing. There are well over 10,000 continuously operating GNSS sites established around the world for such activities as crustal deformation studies, subsidence monitoring, absolute sea level measuring, surveying and navigation. However, scientific studies in GNSS has led to the development of many other application that were not envisaged when those satellite systems were originally designed, for instance measurement of the ionosphere and troposphere. Recently a novel application has been the utilization of one the major error sources in the technique; interference from reflected (and diffracted) GNSS signals from the, primarily near field, environment.

For a horizontal planer surface, such as the sea, the interference pattern as seen in the recorded signal strength is directly related to the height between the antenna and the surface. Therefore, any GNSS instrument sited very close to the coast can potentially be used to measure sea level. Measuring sea level remotely can be an attractive idea. There are many environments, locations or times where a conventional tide gauge may not be suitable, unlikely to be maintained or too costly for the work being done, for instance during a field experiment where approximate knowledge of the tide is all that is required. A GNSS-MR tide gauge could be installed in a rocky environment or high on a cliff face. GNSS equipment is generally easier to install, deploy and maintain with less specialist skills required and are less susceptible to such things as fouling or damage from boats.

In this talk we explain the method and demonstrate its use using GNSS "sites of opportunity" from around the world already established for geodetic studies. Typical uncertainties are on the order of 3-20cm RMS. While sites using multipath interferometry require no specialist or modified equipment they are equipped with high-end geodetic receivers and antennas that are needed to measure position to sub-centimetre levels. These receivers are not necessarily cheap and the antennas have one big disadvantage for this work: they are built to inhibit multipath reflections from low elevation angles. We will also show preliminary results of an ongoing project that uses a sub £100 antenna. Such a system could revolutionize sea level measurements by allowing many more tide gauges to be established at a fraction of the cost.

Approaching the Coast with Significant Wave and Sea Surface Heights from Satellite Altimetry
by Nadim Dayoub, Ocean Altimetry Development Specialist, NOC Southampton

Altimetry in the open ocean has been proven as a significant tool for ocean sciences in providing global information on sea level heights, significant wave height (SWH) and backscatter coefficients that are used to deduce wind speed. However, the standard retrieval of these quantities has been problematic closer to coast due to contamination of the waveforms by land and calm water interference. Much work has been undertaken to improve the quality of retrievals in the coastal zone including re-tracking data closer and closer to land.

The Adaptive Leading-Edge Subwaveform (ALES) re-tracker developed at the National Oceanography Centre (NOC; Passaro et al., 2014) has been a key component in re-tracking data closer to the coast. ALES has the capability to maintain the processing accuracy in the coastal area and the open ocean by adapting the width of the estimation window based on significant wave height (SWH). This re-tracker can re-track waveforms from all pulse-limited altimetry and has already been implemented at NOC for Jason-1, Jason-2, Jason3, Envisat, SARAL/Altika missions and the pseudo low resolution mode of Sentinel-3A.

In this talk, we will present the techniques, results and the recent advances in accessing and processing altimetry in the coastal zone.

Remote sensing of coastal hydrography using marine X-band radar
by Dr David McCann, Marine Physicist, NOC Southampton 

For the last 20 years the National Oceanography Centre has been at the leading edge of ground-based remote sensing of coastal seas using X-band marine radar. Using commercially-available off-the-shelf equipment NOC has developed a suite of analytical techniques that enable the determination of a host of hydrographic parameters including shallow water (<50m) bathymetry, tidal currents and surface wave spectra as well as showcasing its use for seabird and marine mammal tracking. Recent developments funded through a grant from the Ministry of Defence's Defence Science and Technology Laboratory (DSTL) have seen NOC radar science transition from shore-based, static radar installations to data collected by a radar on a moving vessel; generating bathymetric and tidal current maps up to 5km away.

This talk will provide an overview of NOC's hydrographic remote sensing capabilities as well as an insight into cutting-edge technologies currently in development.


All members and and non-members welcome.

A selection of cold food and drinks will be available from 18:30 and presentations will start at 19:00 prompt. 

Please register for this event in advance 

There is a charge of £10 for admission payable online during registration to cover catering (please ask at the door if you require a receipt). Admission is free for full-time Students.

For further information please contact scotland@ths.org.uk

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