A step improvement in the planning and maintenance of on- and off-shore wind farms is happening with the aid of technology led services by specialist operators. This is particularly evident with the rapid evolution of Unmanned Aerial Vehicles (UAV) and Remotely Operated Aerial Vehicles (ROAV). The services provided by experienced land surveyors and inspection engineers combined with skilled pilots and these small flying vehicles is providing dramatic cost savings and improvements in safety to the renewables industry.
This article covers land surveying services using UAVs to improve the planning and monitoring of the construction of new projects and inspection services using ROAVs to improve the maintenance of assets once operational.
The quality of geospatial information is at the heart of all planning and design for any new renewables development. Accurate and reliable topographic survey information is vital – from scoping right through to design and construction. Good visual data of a location can really improve not only the project team’s understanding of the site, but also the team’s decision-making process.
Traditional land surveying methods are very labour intensive, requiring the surveyor to cover every inch of a site in order to take observations using GPS or total station instruments. This process can be very time-consuming, with a surveyor covering 5-10 hectares in a day depending on site conditions — which can be highly challenging. Renewable projects and their related infrastructure are often situated in hostile environments (hilltops, moorlands, remote valleys, cliffs and tidal areas), so when a survey lasts for several weeks, the exposure to risk at such sites can be significant and protracted.
In the last few years, UAVs have been developed to acquire high-resolution aerial imagery. Recent advances in battery technology, miniature autopilot systems and digital cameras have allowed the development of robust and compact unmanned systems suitable to acquire commercial-quality aerial imagery.
In the renewables sector, UAVs are used to acquire high-resolution aerial imagery and process the results using advanced photogrammetry software to generate accurate topographic survey information, orthophotos and oblique panoramic images. This advanced technology has revolutionised the acquisition of site data at these often remote sites.
UAV-acquired information is highly beneficial for assessing potential site locations, designing site layouts, generating 3D visualisations, assessing site visibility, calculating earthworks volumes, monitoring construction progress and producing as-built records.
Benefits of UAV surveys
Small UAVs, operated by experienced and skilled professionals, can provide a step improvement in survey data collection. The accuracy of the survey information derived by UAV is in the region of 100mm vertically and 50mm horizontally, depending on the required resolution of the images and the number of ground control points. This resolution is sufficient for most renewable projects.
Up-to-date UAV digital images are also beneficial to a project because online resources such as Google Maps are, typically, out of date and of very low resolution at the remote sites where renewable projects are frequently situated.
A UAV can easily survey more than 100 hectares in a single day. This means that the survey can be much more cost-effective than traditional land surveying, with the additional benefit of high-resolution imagery. A UAV survey team needs only limited ground access during the survey, which reduces the exposure to risk and the ability to survey hostile environments.
Following are some of the main benefits of a UAV survey when compared to a traditional land survey:
- UAVs are more cost-effective
- The site work can be carried out more quickly
- There is reduced exposure to risk for surveyors
- Limited ground access is required on site
- Inaccessible/hazardous areas can be surveyed remotely
- UAVs offer in improved data – topographical information plus high-resolution aerial imagery
Inspection using ROAV
ROAVs have been utilised for onshore and offshore inspection services in the oil and gas and utility industries in the UK, Europe, Asia and the Middle East. With more than 200 flare inspections and over 1500 transmission tower inspections completed over the last few years, this inspection solution is now becoming established as best practice in these industries. This technique is now being applied in the renewables industry with the inspection of structures such as wind turbine blades and met masts.1
Land Survey Case Study
In a recent development project in South-West Scotland, a wind farm developer had considered alternative survey methods, such as traditional land-based surveys and manned aerial LiDAR surveys. The operator concluded that UAV technology would be the most efficient way to survey the site. Decisive factors included time saved, the reduced risk to subcontractors and the quality of data produced by the UAV methodology. The purpose of the survey was to provide data to assist with the planning, design and construction of the site, which covered more than 400 hectares of moorland and bog with limited access.
The deliverables from the survey were highly detailed geo-referenced orthophotos and an accurate Digital Elevation Model (DEM). In addition to the information acquired from the air, the Cyberhawk team added some ground survey information such as culvert levels using GPS equipment.
The detailed orthophotos2 revealed previously hidden detail, including a watercourse that was not shown on ordnance survey mapping and was previously unknown to the client. The combination of detailed topographic information together with vertical and oblique photography of a proposed site provides windfarm developers and the renewables industry with enhanced data to allow improved decision-making on their sites in a cost-, time- and safety-efficient way.
Methodology
The process of carrying out a topographical survey is not simply a case of flying a UAV around a strip of land. It requires care, experience, pre-planning and careful coordination. Following are the critical steps to be taken:
- Ground control points are established across the area of interest and are precisely positioned using GPS equipment.
- A flight plan is prepared, taking into account the area to be surveyed, wind direction, take-off and landing areas, image resolution required and maximum flying height. This requires experience and skill to ensure the data is captured to the correct specification and safely.
- The flight plan is then uploaded to the UAV wirelessly.
- The UAV is launched and will follow the flight plan using the on-board autopilot system. A series of overlapping vertical images are taken at locations defined in the flight plan. Once the flight plan is completed, the pilot will land the UAV in a suitable location. Note: It is important that the pilot is well trained and experienced so that the UAV is landed safely in any site conditions and that they can take control is there are any problems with the autopilot.
- The images and GPS photo logs are downloaded from the UAV. When processing the data, the ground control points are identified and co-ordinated in the photos. The software uses photogrammetric principles to calculate the topography from the numerous overlapping images.
- The resulting output is a digital elevation model (DEM) which can be produced on a grid <1m and geo-referenced orthophotos.
- UAV survey data is issued to the client in formats that will be compatible with standard software packages such as AutoCAD, Civil 3D and ArcGIS. Geo-referenced imagery is supplied in standard image formats, such as jpeg, png or tiff.
Offshore site challenges
Inspection standards and procedures for offshore wind turbines comparatively more challenging than those established for onshore applications. These inspections are especially challenging due to the extreme conditions and access problems found in offshore environments. This is driving the industry to look beyond traditional inspection techniques in a bid to find more rapid, effective and reliable inspection methods.
By comparison, with onshore wind farm inspections are facilitated via rope access, mobile elevated work platforms (MEWPs), scaffolding and manned baskets are traditionally used for turbine inspections. However, in an offshore environment MEWPs and manned baskets cannot be used (accessing the turbine is problematic for rope access and scaffolding is expensive and time-consuming). In these situations, ROAV inspection techniques can dramatically reduce project safety risk, reduce costs, increase inspection speed and ensure consistent and valuable data provision.
In all its applications, the ROAV inspection methodology entails taking people out of hazardous environments. In the context of offshore turbine inspections, the ROAV inspection allows operators to inspect turbines significantly faster than would be possible using rope access.
For example: a field of, say, 150 offshore turbines can be rapidly inspected using the ROAV technique. Armed with this information, the wind farm operator need only climb the turbines that require repair or further assessment, rather than climbing all turbines as may be the case with traditional approaches. This represents savings in both cost and time, while limiting the risk to which inspectors are exposed. In other words, they don’t have to climb turbines unless an identifiable defect requiring repair has been established.
Inspection Case Studies
In December 2012, Cyberhawk completed an offshore wind turbine inspection in the Irish Sea for a major wind turbine manufacturer. Operating from an offshore supply vessel, the inspection highlighted the effectiveness of the method in inspecting the blades, nacelle, tower and transition piece. As part of its effectiveness, it has demonstrated the high-quality information, images and reporting that can be achieved.
Development of the technique in the offshore renewables sector has also included carrying out multiple metrological mast inspections, covering both coating condition and the mast’s structural integrity. The value of the technique was recently illustrated by being able to complete a detailed inspection while operating with a 250 metre exclusion zone around the metrological mast. The ROAV was able to fly close to the “met” mast while operators remained beyond the exclusion perimeter, receiving live HD video footage and imagery from the vehicle as it carried out a full condition inspection.
Earlier this year Cyberhawk carried out a close visual inspection of the two recently installed metrological masts on Dogger Bank in the North Sea using a ROAV. During the construction of the met masts, paint marks had been put on the bolt heads and nuts of the flanges to mark their ‘as-installed’ positions. The main purpose of the inspection was to ascertain if any of the bolts had rotated since installation. During the operation, other parts of the masts were inspected. These included the aviation lights and anemometers as well as the underdeck area.
About Cyberhawk
Remote aerial inspection and land surveying company Cyberhawk Innovations has been at the forefront of developing UAV & ROAV land survey and inspection services. Over the past five years, the company has developed a unique combination of experienced land surveyors, pilots and cutting-edge UAV technology to provide a high-quality and consistent service to the utility and renewables industry.
REFERENCES
1. Cyberhawk won the Oil & Gas UK Business Efficiency Award (jointly with Stork Technical Services) in November 2012 for its aerial surveying techniques. The award was for the use of ROAV technology to inspect the paint condition on an offshore drilling derrick on Shell’s Brent Delta platform. This was the first use of this technology in the North Sea, which ultimately saved the client £4.6m.
2. Orthophotos are aerial images with a uniform scale similar to a map. These can be provided at resolutions down to 2cm/pixel.