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A low cost (US$30) consumer grade GPS receiver with a sideways mounted antenna has been applied to measure tidal water levels at a meso-tidal coastal site using an interferometric reflectometry approach. The proof of concept system was installed approximately 16m above mean sea level in close proximity to a conventional bubbler tide gauge that provided validation data. The received Signal to Noise Ratios (SNR) for the satellites in view were recorded for several months during two successive years and the observed frequencies of the interferometric oscillations used to calculate the difference in elevation between the receiver and the water surface. Comparisons with concurrent and historic in situ tide gauge data at the site initially helped to identify a calibration issue with the in situ gauge. The GPS based measurements were shown to be in excellent agreement with the corrected in situ gauge, exhibiting a Root Mean Square difference of 5.7cm over a tidal range exceeding 3m at spring tides and a daily averaged RMS of 1.7cm. The SNR data from the low cost GPS receivers are shown to provide significantly higher quality data for this purpose compared with high end geodetic grade receivers at similar sites. This low cost, widely available technology has the potential to be applied globally for monitoring water levels in a wide variety of circumstances and applications that would otherwise be cost or situation prohibitive. It could also be applied as an independent cross check and quality control measure for conventional water level gauges.

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Please cite this article as: D.L. McCann, P.S. Bell, Visualising the aspect-dependent radar cross section of seabirds over a tidal energy test site using a commercial marine radar system, (2017), doi: http://dx. AbstractThe long-term monitoring of seabirds around proposed marine renewable energy (MRE) sites is vital to assess the large-scale and long-term environmental impacts of MRE installations. Marine radar could be a valuable tool to augment traditional seabird surveys but the problem of aspect dependency of the generic radar cross section (RCS) of live birds in flight must be understood before radar data is correctly interpreted. A marine radar multiple target tracking algorithm ('GANNET') was applied to data from an un-calibrated, horizontally polarised, 10kW X-band marine radar sited at the European Marine Energy Centre (EMEC) tidal renewable energy test site, Scotland U.K. From 24 days of data over 1.84 million target readings were recorded. For each target reading the radar aspect angle (bearing of radar beam incident on target), range and non-dimensional echo magnitude were derived allowing a view to be generated of the variation of echo magnitude with aspect angle for all tracked targets. The resulting polar diagram shows a significant change in echo magnitude with range between side-on and head/tail-on aspects indicating a large contribution of the RCS from the wings of birds in flight. The species-unspecific detectability of seabirds, especially at long range, is found to be strongly dependent on aspect angle. This has direct implications for the use of marine radar equipment for avian monitoring at proposed and active marine energy sites and must be taken into account if data from these radars are to be used to augment traditional bird abundance and area use surveys conducted by human observers.

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