Met Office: Wavenet and HF radar

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Wavenet and HF radar

What is Wavenet

Wavenet is a project commissioned by Defra that aims to construct a near shore wave monitoring network for England and Wales. As part of this project the Met Office is conducting the trial of an HF radar system to evaluate the usefulness of the technology, which has already demonstrated many advantages over traditional wave buoy measurements. The Met Office is currently partnering with Neptune Radar and the University of Sheffield to deliver a cost-effective wave monitoring solution that will complement buoy and satellite observations.

Defra has funded this three-year study to find ways of monitoring wave height and direction in order to improve forecasts of coastal flooding. Large-scale continuous monitoring of wave characteristics will produce a near shore wave climatology to help improve understanding of coastal erosion risk and the design of coastal erosion defence works.

What are the benefits of HF radar

HF radar offers significant benefits compared to other wave measurement methods. The table below summarises some of the main strengths and weaknesses of wave measurement methods.

Method	Pros	Cons
HF radar	Detailed measurements of wave, wind and current information. Good temporal coverage, addressing the stated requirement for continuous monitoring. Good spatial coverage. Easy to service and maintain – no ships required. No risk of shipping/fishing incidents.	Expensive (4x cost of buoy) but can provide more information than several buoys. Availability of suitable sites. Planning permission can take time to come through.
Wave buoy or ADCP with wave measurement capability	Good quality measurements of wave height, period and direction.	Frequently hit by shipping, caught in fishing nets. Expensive and difficult to service and replace – need ship time and weather windows therefore difficult to maintain a continuous wave climate record. Point measurement, poor spatial coverage.
Fixed platform e.g. oil rig	Reasonable wave height measurements. Robust against shipping/fishing accidents.	Expensive to service – e.g. helicopter visit. Lack of detailed wave information e.g. directional spectra. Point measurement, poor spatial coverage.
Light vessel	Reasonable wave height measurements. Robust against shipping/fishing accidents	Not particularly accurate wave measurements. Non directional. Expensive to service – need ship time and weather windows. Point measurement, poor spatial coverage.
Satellite radar instruments e.g. Radar Altimeter (RA), ENVISAT-ASAR	Good spatial coverage for ASAR but not for RA. Accurate wave measurement. No maintenance after launch. No risk of shipping/fishing incidents.	Poor temporal coverage, satellite overpass usually every few days.

How does the radar perform compared to other sources of wave data

The Met Office is conducting a trial of a radar system (PISCES), which is set up to observe the Bristol Channel and Celtic Sea. The aim of the trial is to prove the long range dual radar technique for the measurement of ocean wave and current parameters. The figure below shows the overlap between two HF radars, which are sited in north Devon and south Wales.

HF radars in South Wales and Devon

The figure below shows what the radar in north Devon actually looks like, with the transmit antenna in the left picture and the receive antennae on the right.

Devon radar transmitting antennae

Data have also been collected from a CEFAS wave buoy and the Met Office wave model for comparison with the HF radar data. The figure below demonstrates the close agreement between the HF radar and the model estimates of significant wave height. Similar agreement has been found when radar wave measurements were compared with those obtained from the wave buoy. The surface currents reported by the HF radar also agree well with estimates made by the Met Office wave model.

HF radar compared with model