NEWS Malta GPS Wave Buoy Interface

The deployment of the GPS directional wave buoy in Gozo forms part of the NEWS (Nearshore hazard monitoring and Early Warning System) project led by the Università degli Studi di Enna “Kore”. The project is partially funded by ERDF funds through the Italia-Mala Interreg V-A Operational Programme (2014-2020). NEWS tackles the coastal erosion risks on the southern coast of Sicily and the Maltese Islands. Coasts are subjected to fast erosion due to natural and anthropic causes which involve the failure of cliffs, the triggering of localized erosions and the possibility of flooding. NEWS deals primarily with the modelling and monitoring of coastal risk processes, including the design of alert components against major risks. The system will make use of an integrated geophysical sensor network on land as well as a networked set of wave buoys installed offshore Sicily and the Maltese Islands.

The NEWS GPS wave buoy deployed in Malta resides at a station offshore Marsalforn (Gozo). It measures sea waves (height, direction and period) and sea temperature in real time. A similar buoy makes the same observations on the side of Sicily. The Malta buoy is maintained by the Physical Oceanography Research Group of the Dept. of Geosciences (University of Malta).
Map showing location of 
                                the wave buoy with bathymetry in the background.
Figure 1: Station position of the wave buoy is indicated by the black spot. Empty circles show the annular wave bins measured by the HF radar at SOPU station in Gozo. The background map shows the sea depth contours in this marine area.
The GPS wave buoy on site.
Figure 2: The GPS wave buoy on site.
The device itself is a small spherical (35cm diameter) field serviceable buoy hull with electronics inside. The station consists of a restrained shallow water near-coastal system with a reference small yellow surface marker attached to a subsurface mooring, to which the device is connected by a 20m cord.  The buoy moves over an area centred at N 36° 04.882’; E 014° 16.875’ within a range of about 200m.

The heart of the buoy is the directional wave spectra sensor which is a high-performance GPS engine paired with software algorithms for onboard computation of the directional wave spectrum with 1/256 Hz bandwidth from 0.03Hz – 0.50Hz and a user programmable sampling window. On-board processing enables the computation of the First-5 Directional Fourier coefficients a0, a1, b1, a2, b2 that are used to compute wave parameters such as significant wave height, swell direction, and directional spread, among others. Sea Surface Temperature is also measured with ±0.05K accuracy.

All measurements collected are logged onboard an optional microSD card as well as relayed by satellite communication to a land receiving station at the University of Malta using Iridium Short Burst Data (SBD) telemetry.

The GPS wave buoy is a low cost new generation of wave measuring devices. Traditional wave buoys are of the gravity-acceleration-type, using a mounted acceleration sensor, an electronic compass, a gyroscope to measure sea waves based on the principle of gravity acceleration. The GPS wave buoy is a new wave measurement method that uses satellite GPS signals to measure ocean waves. It calculates the movement velocity of the buoy using the Doppler frequency shift of satellite GPS signals, which are then used to calculate wave parameters. This makes the GPS wave buoy a very versatile, small-sized device which only needs a simple GPS sensor. Advantages over the gravity-acceleration-type wave buoys are:
  1. (i) no need of regular calibration since satellite GPS signals do not further undergo measurement errors due to increases in usage time,
  2. (ii) measurements are not affected by any on-site magnetic parts, and
  3. (iii) it is able to measure longer period waves.