Robert Peel, GIS and Technology Consultant, UK
Airborne surveying has been revolutionized in recent years with increasingly detailed and up-to-date digital surveys. The demand for seamless and countrywide aerial photomaps to support consumer products like Google Earth has made aerial mapping very much mainstream and has resulted in important spins offs for both government and industry.
New generation digital aerial cameras and advanced processing software allows three-dimensional data to be collected that in turn allows 3D models to be created. Survey aircraft can also be equipped with other remote sensing sensors, such as laser scanners and thermal imagers to capture every detail of the land and infrastructure, including information not visible to the human eye.
Thermal surveys for example are increasingly being undertaken across Britain’s cities. Normally commissioned by local authorities and undertaken by companies such as aerial mapping specialist Bluesky, the survey aircraft fly on cold winter nights to determine the heat loss from properties. In Luton in the UK, for example, data has been matched using a Geographic Information Systems (GIS) to property level maps so that residents can see the heat loss from their own property.
“The thermal images are a very good way of showing residents how much heat they are losing through the roofs of their homes. People can see how heat efficient their property is by its colour and they can compare its heat efficiency to neighbouring houses which may be the same type of building, but are more heat efficient due to better roof insulation,” said Donald Bowler, Luton Borough Council’s environmental assessment manager.
Looking from above
Bluesky’s main activity, however, is aerial photography, and the Leicestershire-based firm has helped the UK’s National Grid explore the potential for underground cabling works. In a recent project, Bluesky imagery was used to enhance a large-scale virtual reality model of the area around a former rail tunnel. Models of this type have previously been used by National Grid to help explore routing options and site planning for new power lines and substations. The 3D imaging technology has now been chosen to help communicate proposals for underground cabling works in the Woodhead rail tunnel on the northeast edge of the Peak District National Park.
The project was undertaken by SLR Consulting, a multi-disciplinary consultancy operating in the UK and North America. “Our model demonstrates the fine detail of the cabling works,” said Peter McGuckin, principal at SLR Consulting. “However with the addition of the Bluesky imagery, the interactive model really comes into its own as a powerful means of showing the landscape context and the minimal effect the proposed works will have on the environment.”
Laser scanning comes of age
The other main area of remote sensing technology involves laser scanning. With recent developments in scanning technology and processing software, new systems are being developed to electronically map and monitor change with greater precision than previously possible.
Laser scanning has been widely used for airborne terrain mapping with airborne LiDAR proving to be an ideal tool for applications such as flood plain mapping. Power companies have traditionally used airborne LiDAR to survey high voltage power networks.
Computer generated 3D terrain model from the UK’s Peak District – being used to plan underground cabling for National Grid
However, airborne surveying does not provide the required accuracy or aspect for many engineering and environmental applications, and this has required the development of special land-based systems. Most airborne LiDAR systems are not eye-safe at short range making it dangerous in populated areas. In addition, field of view is usually limited and the GPS/Inertial Navigation System (INS) is not effective when satellite visibility is obscured by vegetation or buildings.
Lasers transmit a light pulse, from a known position and at a known angle, which is reflected off a surface or feature and bounced back to a receiver. Using the time taken for each individual pulse to be returned and the known value of the speed of light the system can automatically calculate the distance of the feature from the unit. From this data highly detailed and accurate 3D models can be produced.
Scanning becomes up close and personal
For power companies, low voltage cables are too small and too close to the ground to be visible. Their size and proximity to both ground and vegetation make them vulnerable to damage therefore increasing the risk of network failure.
This has led to a demand for laser scanners that are safe and convenient to use at ground level. Austrian firm RIEGL has designed highly portable scanners that can be used just about anywhere, prompting developments by a specialist company called 3D Laser Mapping, which is looking at ways of speeding up data capture by taking advantage of the added portability of the RIEGL scanners.
One of the first commercial system involved mounting lasers on a specially equipped quad bike. This has been used for capturing millimetre-accurate measurements of the UK coast to create a 3D model of the rock and soil surface. “Laser scanning allows us to record changes in the rock structure that would be difficult and time consuming to detect using our existing surveying techniques,” said Stuart McVey, coastal surveyor. “When you also consider the speed at which the data is captured and the fact that we can remotely access unsafe or otherwise inaccessible parts of the rock structures, this technology gives us very valuable data and provides good value for money.”
Even greater portability is offered by an innovative system that can be carried as a backpack. This has been developed to map overhead infrastructure such as power lines. With power outages becoming more common in both Europe and North America, one key risk is the increased vegetation growth rates, and with big storms in recent years, laser surveys offer a solution for mapping overhead cables and surrounding vegetation to better assess areas of high risk so that maintenance can be prioritized.
The system instantly maps the proximity of vegetation to overhead cables. Special software automatically identifies potential conflict between cable and vegetation, determining the level of risk, backed up with images from an integrated digital camera. By maintaining accurate and up to date records of the infrastructure and nearby vegetation proactive maintenance can be scheduled and the risk and liability reduced.
A similar system has also been developed for mapping overhead telecom networks. In this case, the 4×4 vehicle mounted WireFinder system accurately measures the position of telecom network assets, such as poles and wires. The WireFinder laser scanner with its 360 degree field of view can capture 12 000 measurements per second, at distances of up to 300 m with a repeatability of less than 10 mm.
Route mapping helps to find the way
A further advance is StreetMapper, which is the result of a joint venture between UK-based 3D Laser Mapping and German guidance and navigation specialist, IGI. The system enables highly rapid and accurate 3D laser mapping from a fast moving vehicle. StreetMapper can measure up to 40 000 3D points per second while in motion, with a typical positional accuracy of 5 mm for good GPS conditions and an average point-to-point accuracy of 3 cm. StreetMapper can also be enhanced with video capture and the addition of other sensors.
StreetMapper-equipped 4×4 vehicle surveying assets along the road
National Grid has already used StreetMapper to survey from Ellesmere Port to its Cellarhead substation in Staffordshire to ensure the route was suitable for transporting a large transformer. Completed in just one hour by driving the length of 19 km route at normal road speed, National Grid found the system much safer than traditional manual surveys; surveying narrow stretches of road, with normal traffic flow can be hazardous. The 93 million points of survey data were then analyzed to highlight problem areas en route called ‘pinch points’.
Interestingly, StreetMapper is also proving its potential for security applications where is can be used to patrol perimeter roads and other high security areas, alerting security officers to tiny changes along the route, such as ground disturbances or out of place objects.
Harnessing the power of robotics
Finally, the latest innovations in laser scanning involve robots used as remote sensing vehicles (RSV). The idea of a RSV for mining was first conceived at the UK’s Camborne School of Mines, and that technology has been employed in laser scanning robot 3D-R1. Developed by Jobling Purser RSV LLP in conjunction with 3D Laser Mapping, 3D-R1 allows 3D surveying to be carried out in dangerous or hazardous environments.
Traditional scanning in hazardous situations often lead to blind spots because of restrictions in access, but 3D-R1 is moved by remote control from location to location, performing scans and video in areas that are otherwise not safe to enter. Even in safe environments, 3D-R1 is a useful tool that can increase productivity by 75 per cent by eliminating the need to manually set up scanners at each location. Being light and easy to use, 3D-R1 can be used easily for many potential applications including underground surveys of tunnels or mines or the surveying of earthquake, fire or blast damaged sites.
Fresh perspective on managing assets
The information provided by new aerial and land surveying technology provides an important new perspective for managing assets. The rapid surveying technology means that much more comprehensive data can be collected on current assets and risks. With considerably improved information at its fingertips, the power industry can make real improvements in efficiency, security, safety and service.