RPS tech: the science behind wind measurement success offshore

Floating LiDAR is a relatively new technology for measurement of wind, wind speed and more – give us quick overview of the science and benefits of using this method.

“LiDAR has been around for a while and is used extensively for mapping the spatial characteristics of built and natural features on land. For this application, the LiDAR device is fixed to a floating buoy and measures the doppler shift/effect (changes to laser light wave formations) as a way of determining wind speeds at sea. 

“In recent years LiDAR has been deployed reliably on floating buoys to measure the wind profile of offshore areas. An upward facing laser is focused at select heights and can measure wind speed characteristics up to 250 metres above the instrument. In the past, measuring wind profiles at sea involved erecting static ‘met masts’ that are fixed to the ocean floor and have instruments called cup anemometers attached to them. This method is much more expensive and doesn't allow you to capture data above 80 metres or so."  

Seems like the demand for floating LiDAR and wind measurement is increasing – which industries are driving this demand and why? 

“Offshore wind farming is one of the main drivers currently as when energy companies are thinking about investing in the construction of offshore wind farms they need to be confident about potential yield - how much wind energy that will be available on average in a certain area.”

RPS has recently designed a set of new floating LiDAR buoys – what’s different about RPS’ design?

"The design is based on our 20 years’ experience building and operating bespoke meteorological and oceanographic (MetOcean) measurement systems that are deployed to complex offshore environments and are serviced infrequently.

“Based on our knowledge and experience of the challenges of capturing MetOcean data, the focus of our design and development process was very much on increasing equipment reliability to maximise data accuracy, and making the process of information gathering easier and more cost-effective for our clients.

“Some of the key features of the design that we particularly focused on include:

• Positioning of the LiDAR unit – our LiDAR equipment is positioned high off the water (2.5 m) and protected from all sides and underneath.
• Simple and renewable power - the power system we designed is all renewable. This is not only good from an environmental perspective but makes permitting much simpler, particularly in countries like the United States.
• Data protection – one of the risks when you deploy buoys offshore is that of data loss when connection to the satellite or power source is disrupted in some way. Our buoys have redundancy mechanisms in place for power and satellite communications and all raw data is exported daily, meaning the risk of data loss is significantly reduced.
• Increased stability – a lot of thought went into the physical design of the buoys to enhance stability. The buoys are large (more than 4 metres across) and have a toroidal (donut) shape, which provides a relatively stable platform for housing the LiDAR equipment.
• Environmentally friendly moorings – unlike many other buoys, the mooring system we’ve designed does not drag chains along the seabed. This means that the risk of environmental damage is significantly reduced.”

You’ve recently completed a six-week test deployment off the coast of Perth – what was the methodology for testing data accuracy? 

“We deployed two LiDAR units 200 metres apart at sea. One was fixed on a navigation pylon (to mimic a standard met mast setup), and the other was deployed in our new floating LIDAR configuration. They were calibrated to measure at the same time and height intervals, so the data from the fixed unit could be used to validate the information captured using the floating device.”

Did anything come out of the test deployment that you weren’t expecting? 

“We did not expect the data from the two independent LiDAR wind profilers (fixed and floating) to align so closely! The agreement between the two was better than 99%, which was pretty astonishing. 

“We also weren’t expecting the winter storms to be so severe! We measured winds that were frequently over 20 metres per second (ms^-1), with wave heights reaching 7.3 m offshore and over 4 m at the buoy location. It really gave the buoy and mooring a good test!"

Offshore environments are by nature very variable. What’s the average timeline for measurement programs for infrastructure such as offshore wind farms? What other environmental variables does your team look at and what other equipment/methods do you typically use? 

“The minimum survey period is one year which allows you to measure across all seasons. Additional years are quite often used to assess inter-annual variability and gain greater confidence in the wind energy available for farming.

“We measure all MetOcean variables to assist with offshore wind farm engineering and as well as many of the environmental parameters required for permitting.

“Examples of the things we measure include weather and wave data, current profiles, water levels and temperatures, sediment data and underwater noise. These are all measured from moored instrumentations, sometimes with the data transmitted in real-time via satellite.”