At Natural Power a recent investment has been made into aerial survey technology to enhance project understanding across all phases of development. This article aims to provide a short review of fixed wing aerial survey technology.
Preparing for Take-off
Through a growing portfolio of clients and project sites, we sought to capitalize on the undeniable benefits brought by aerial survey technology. Principally, this technology investment has been made to augment a ground-based topographic survey capability. However, with the addition of aerial survey this has enhanced many elements of our consultancy business. From scanning ecological habitats and assessing environmental impact, to ensuring terrain is safe and stable for design, construction and operation, aerial surveying is proving to be the go-to technology.
We are frequently given the challenge of new and existing project sites which need to be rapidly assessed across a variety of disciplines. Large-scale renewable sites ranging 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.
3D terrain model of hydro scheme — Scotland, UK
As the potentials of sites are realized, protection of assets into the future also becomes critical to clients. Therefore, long-term monitoring of sites can also be a specific requirement for surveys. 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.
Our initial technology review identified several aerial survey platforms offering fixed wing terrain imaging. The Trimble Navigation ‘UX5’ aircraft model was selected based on its wide operating envelope and ability to work well within the Trimble ecosystem of ground-based GPS and survey equipment that we own and operat. 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 Trimble UX5
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.
UAV Terrain Survey
A short summary of the aerial imaging process is detailed below:
Following preplanning and safety checks for the project area, the UX5 system is pre-programmed by the survey engineer to conduct single or multiple flight missions to achieve the required project coverage. Terrain, wind speed, and suitable take-off / landing sites are all accounted for by the survey engineer during pre-flight. Appropriate flight elevations are selected along with suitable image overlap criteria to ensure the highest 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, employing a 24megapixel image sensor and a custom wide angle lens. This format ensures image data is captured across a suitable area and to a very high quality. Images are recorded at set 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 process, linking each aerial image with a location and flight orientation, is the basis for the post-processing and photogrammetric computations. Numerous ground control stations, accurately surveyed and included in the imagery, allow for absolute adjustment of the data to engineering survey grade quality.
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 in stunning detail.
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. A complete dataset will likely comprise millions of individual data points.
High Flying Results
Through Natural Power’s acquisition and initial training with the Trimble UX5 system, a wide variety of benefits have been realized. The system has proved to be reliable, providing detailed topographic data and imaging, suitable for civil engineering, construction planning and environmental assessment. 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 largescale renewable and wind energy schemes.
Tablet PC – Pre-flight Setup
Time on site has been reduced significantly. This change 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 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. 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.