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CASE STUDIES

This article, published in Wind-Tech International in May 2016, provides a short review of the experiences of Natural Power as they integrate Trimble UX5 fixed-wing aerial survey technology into their existing workflow. Read on for a well written and honest appraisal.

Aerial Surveying for Renewable Projects

 Becoming Flight Ready with the Latest UAV Systems 

NatPower UAV fig 1Natural Power is an independent renewable energy consultancy renowned for early adoption of successful technologies. Understanding complex environments and engineering challenges is the focus of a large number of renewable energy experts who make up this organisation. A recent investment has been made into aerial survey technology to enhance renewable project understanding across all phases of development. This article aims to provide a short review of fixed-wing aerial survey technology, details of equipment, key deliverables, primary benefits and safety controls. There are undoubtedly many unmanned aerial vehicle (UAV) manufacturers and systems available, with technology continually advancing. This review examines Natural Power’s experience in acquiring a Trimble Navigation ‘UX5’ aerial imaging platform.

 By Gavin Germaine, Senior Geotechnical Engineer, Natural Power, UK

 UAVs, drones and RPAS (remotely piloted aircraft systems) are just a few of the increasing numbers of terms used to describe the rise of latest technology to enter the skies.

  The Challenge Ahead

 NatPower UAV fig 2Through a growing portfolio of clients and project sites, Natural Power has sought to capitalise on the deniable benefits brought by aerial survey technology. Principally, this technology investment has been made to augment a ground-based survey capability. However, a wide array of additional benefits has the potential to enhance many elements of Natural Power’s consultancy business. From scanning ecological habitats and assessing environmental impact, to ensuring terrain is safe and stable for design and construction, aerial surveying is proving to be the go-to technology.

 

NatPower UAV fig 3We are frequently set the challenge of new and existing project sites which need to be rapidly understood and assessed across a variety of disciplines. Large-scale renewable sites from new wind projects to hydro schemes can cover mountainous and complex terrain. The full gamut of technical surveys is required, covering aspects of wind physics, ecology, hydrology, geotechnics, civil engineering and construction. As the potentials of sites are realised, protection of assets into the future becomes critical to clients. Therefore, long-term monitoring of sites can also be a specific requirement. Aerial surveying can play an important role, where large areas of coverage can be captured at maximum detail. This can be augmented by an approach for multidisciplinary data sharing that allows for rapid and efficient workflows for site assessment and design.

 

 Equipment Selection

 Natural Power’s initial technology review identified several aerial survey platforms offering fixed-wing terrain imaging. The Trimble Navigation ‘UX5’ aircraft model (Figure 1) was selected based on its wide operating envelope and ability to work well within the Trimble ecosystem of ground-based GPS and survey equipment. Trimble promoted the UX5 as ‘a platform ready to deploy in the field where survey flights are able to be conducted in a fully autonomous and safe manner from launch to landing’. The claim of fully autonomous although accurate may be misinterpreted; the system ensures pilot control and intervention can be instigated at any time from a safe operations perspective. The UAV can be paused, recalled or repositioned at any time during flight, with multiple levels of failsafe to ensure safety and that the equipment is preserved.

  

The Process

 A short summary of the aerial imaging process is detailed below: 

  • NatPower UAV fig 4Following pre-planning and safety checks for the survey area, the UX5 system is pre-programmed by the survey engineer to conduct single or multiple flight missions to achieve the required coverage. Terrain, wind speed, and suitable take-off and landing sites are all accounted for by the survey engineer during pre-programming. Appropriate flight elevations are selected along with suitable image overlap criteria to ensure accuracy of the photogrammetry process. On site a bespoke launcher is assembled and an electronic pre-flight check is followed prior to launch.

  • Digital images are collected on a modified mirrorless digital camera (Figure 2), employing a 24-megapixel image sensor and a custom wide-angle lens system. This ensures image data is captured across a suitable area and to a very high quality (down to a resolution of 2cm). Some basic photography principles are applied to ensure correct shutter speeds are selected for the flight accounting for light conditions. Images are recorded at intervals during the flight mission and saved to a memory card within the camera body. Persistent GPS and flight orientation data is recorded by the UX5 autopilot and also stored on board for download at the end of the flight.

  • A digital tie-point, linking each aerial image with a geolocation and flight orientation, is the basis for the post-processing and photogrammetric computation. Several ground control stations, accurately surveyed and included in the imagery, allow for absolute adjustment of the data to survey grade. Back at the office, post-processing software which is supplied by Trimble facilitates location calibration and photogrammetric computations. The algorithms in the software perform the necessary adjustments, with an initial ‘point cloud’ data output of 3D spatial data in a basic x, y, z format. Further processing allows for a mosaic of the imagery at high resolution which can be presented in 2D map form or draped over the digital terrain data to form a 3D surface model and representation of the project site.

  • Data can be shared in a variety of formats with final deliverables ranging from high resolution 2D imagery to 3D AutoCAD models suitable for civil engineering design. An example high detailed point cloud sample is shown in Figures 3 and 5. A complete dataset will likely comprise millions of individual data points.

  • Survey Procedures

    In the UK it is vitally important to ensure appropriate permissions are sought with respect to conducting aerial work. Permission is administered by the Civil Aviation Authority, who will expect a minimum level of ground-based theory training and flight assessment before permissions are granted. Similarly, the National Aviation Authorities (NAAs) across the EU and the Federal Aviation Administration (FAA) in the USA have strict regulation on private NatPower UAV fig 5and commercial UAV deployment. Anyone interested in pursuing this technology should seek further information from their relevant authority.

    Safe deployment requires essential pre-planning, landowner permission and a good understanding of the prevailing weather conditions. The Trimble UX5 can be fully pre-programmed with flight missions prior to arriving on site to ensure the full scope of the survey can be accommodated safely and efficiently. Using coarse resolution aerial base maps and traditional GIS mapping facilities there is an efficient workflow possible to conduct the pre-planning phase back at base. Often planning may be supplemented by civil aviation maps and databases as well as liaison with the relevant air traffic control sector for the planned operations.

    On site the UX5 is launched from a bespoke elastic powered launcher, to ensure the aircraft reaches take-off speed reliably and in a controlled manner. Ground control software drives pre-flight checks where the aircraft is visually inspected, data is uploaded and on-board sensors are tested. It would be usual to conduct flight operations with a team of two, comprising the pilot in command and a visual observer to aid in the spotting of hazards and coordinating operations on the ground (Figure 4). Pilots who are trained surveyors and engineers can be a great benefit when optimising surveys for the best possible results.

    NatPower UAV fig 6The UX5 is constructed of an impact-resistant foam structure and internal and external composite elements including carbon fibre. These materials offer a high grade of strength and durability. Trimble still indicate that some degree of wear and tear is envisaged for this system under high workloads, and therefore the aircraft design allows for quick plug and play replacement of flight control units and electronics at the user’s discretion.

    As mentioned earlier, the flight envelope is a key strength of the UX5, ensuring a wide range of available operating conditions. We have found the system can typically fly survey missions for up to 35 minutes. This may be extended in more optimal flight conditions. The UX5 is able to reliably deliver high quality results in wind speeds of up to 65km/h (40mph) and in light rain. The ground control unit maintains a strong signal link with the UX5 during flight through a 2.4GHz radio link. This allows for real-time monitoring of survey progress and flight telemetry.

    Natural Power has worked with Survey Solutions Scotland, an experienced and approved equipment supplier, from purchase of the aerial survey equipment with continued training support.

     

    Conclusion and Discussion

    Through our acquisition and initial training with the Trimble UX5 system, a wide variety of benefits have been realised. Our first batch of test data from the system has been analysed and compared with equivalent differential ground-based GPS; results are concluded to be of comparable quality. The system has proved to be reliable providing detailed topographic data and imaging, suitable for civil engineering and construction planning. Detailed high resolution imagery provides the opportunity to map geomorphological features in detail. This leads to an increased understanding of landslide risk and terrain stability, which are vital factors for planning large-scale renewable and wind energy schemes.

    It has been found that the software processing of the data requires a very powerful computer system. Photogrammetric algorithms and photo adjustment can require significant time to process. A typical large-scale wind project may require 24–36 hours in data processing alone. However, this process is autonomous and can be left to run on a server or workstation unattended.

    Data management becomes an increasingly important issue due to the volume of data yielded by the aerial survey system. We have established a dedicated storage array to host the terabytes of raw imagery data which will be yielded over the coming year. There will be future challenges to ensure the data is shared in the most efficient manner in order to maximise its benefit. Further research is ongoing with regard to various web platforms and geographic information systems to enable data sharing with internal project teams and to external clients.

    Time on site has been reduced significantly for the traditional ground-based survey teams. This has resulted in a lower exposure to environmental hazards, including access across very difficult terrain. Typically, a project area of the order of 5km2 can be surveyed in a single day, allowing the focus to move back into the office, where fast computation and output survey data can translate into more time to work on planning and design.

    Ultimately we have found the adoption of aerial surveying by UAV to be an exceptional tool in rapidly understanding a site and providing a data-rich source of information to drive forward development from the earliest opportunity (Figures 5 and 6). With increasing amounts of uncertainty in the market, ‘light or no footprint’ survey and data gathering is seen as an ideal approach for the renewable energy industry.

     

    Biography of the Author

    Gavin Germaine is a Senior Geotechnical Engineer with Natural Power. He has worked across a wide portfolio of onshore and offshore renewable projects and managed geophysical and geotechnical investigations, with further development of aerial survey capability and advancement in geotechnical design. He holds a Masters in Engineering Geology from the University of Leeds.

     

     

 


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