Charging Ahead

April 29, 2009
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A Merrick surveyor locates property corners as part of a power line survey.


In today’s energy-demanding world, much focus is being placed on the development of clean and alternative energy sources. These applications are creating numerous opportunities for the use of surveying and remote sensing technologies.

In renewables, where energy is generated from continuously replenished resources such as wind, sun and geothermal sources, the most obvious application of these technologies lies in the planning, design and construction of wind and solar farms. Integrating topographic data with historical climatic and weather patterns can help identify the optimum locations for these energy sources, and the transmission of power from those farms will provide opportunities for typical route surveying, property ownership research, deed and easement legal descriptions.

In biofuels, where living and recently dead biological materials such wood, grain and algae are used to produce energy, remote sensing, survey and geospatial roles expand the more-traditional services to include site development of new production plants, market location analysis, volume of biological material predictions and source-to-user vicinity studies. Initially, locating and quantifying the volume of biological materials can be accomplished using multispectral satellite imagery and hyperspectral sensors, which detect unique light and reflectance responses from the source. More traditional surveying and mapping technologies can be deployed once biofuel plants go from the concept phase into design and construction and, finally, distribution since pipelines will be needed to transport the biofuel to the end-user.

And in the traditional distribution and transmission field, power producers are looking to push more power through existing systems and develop new corridors for the distribution of new energy resources. The use of more-modern surveying and mapping techniques such as mobile high-definition scanning and airborne LiDAR can expedite this type of analysis.

In all of these areas, the development of the infrastructure needed to transmit energy from the producing source to the end-users will create significant growth prospects for surveying and mapping professionals.

Figure 1. The life cycle of a power line project.

Combining Surveying and Remote Sensing

In many cases, the life cycle of a power line project includes a planning and route-selection phase, an engineering design phase, a construction phase, and an operation and maintenance phase. The requirements--and challenges--for surveys, maps and geospatial data differ for each of these phases. Figure 1 illustrates the project life cycle and provides a few examples of the data and service requirements and primary issues in each phase.

Planning and Route Selection

The process of determining where to construct transmission lines has many intricate and interrelated steps. This well-documented series of processes can be expedited by the use of modern survey, mapping and remote sensing technologies. For example, the use of high-accuracy satellite imagery with submeter pixel resolution, such as the imagery from GeoEye 1, can cover a large corridor of land along a proposed route. Analyzing the multispectral bands of satellite imagery can also produce an initial inventory of many land cover and land use types such as urbanization, natural vegetation and agricultural land. This data source can provide initial points of access for geotechnical studies and points of intersection surveys.

Automating the property deeds and plats from the city and county records can offer quick analysis of the number of landowners that may have to be contacted to enter their property legally. Many survey CAD and GIS software packages can also import digital versions of public property records for this initial planning step. There are several commercially available terrain data sources that can also be used during the planning phase to analyze preliminary slope and drainage concerns.

One of the many challenges in traditional and new remote sensing technologies centers on the word “remote.” During the initial planning of transmission corridors, traditional survey methods can take time and can be intrusive on the environment and landowners. Traveling to, from and along a power-line corridor can add more challenges as landowner relationships and access to private and public lands are always major issues. Environmental concerns can contribute to the challenges of identifying wetlands, endangered plant species and animal habitat, agricultural land, wet and impassible soils, and heavy vegetation. Surveyors, remote sensing scientists and mapping professionals have increasingly begun working together to create combined solutions to address these types of challenges.

Wetlands polygons automatically derived using 128-band, 1-meter hyperspectral imagery.

More-Accurate and Less-Invasive Route Design

Once a preliminary route has been selected, the use of airborne remote sensing technologies can reduce the “boots on the ground” impact of the traditional surveyor. The airborne approach alleviates many of the stresses caused by the surveying process since landowners are often unaware that sensing platforms are present given the altitudes at which most corridor projects are flown. The use of co-mounted digital aerial photography with LiDAR is a powerful combination of sensors that is now being used to produce more-accurate planimetric and topographic databases. These sensors are oriented to real-world coordinates by a network of ground control check points and control base stations occupied using GPS during the flight. Using onboard GPS and inertial measurement unit (IMU) technologies has also increased the horizontal and vertical accuracy. These airborne orientation technologies reduce the number of ground control points, which saves time and money. Also, depending on the accuracy requirements and data feature content, these sensors can be mounted in either a fixed-wing aircraft or a helicopter.

Sensors that can accurately identify endangered species, wildlife habitat, soil types and wetlands can also be co-mounted in the air platform. These additional sensors share the orientation system with the other mapping sensors so that all of the information collected during the flight is coregistered. This recent advance produces more valuable results for planners, civil engineers, geologists, hydrologists and environmentalists.

A Merrick surveyor gathers substation infrastructure details.

Higher Productivity on the Construction Site

New surveying and mapping technologies--such as survey instruments that combine GPS and total station capabilities--can increase productivity at the construction site. For example, the Leica SmartStation offers quicker instrument setup and field surveying, which can save time and increase accuracy. Such technologies increase the productivity and reliability of staking transmission line towers and surveying line crossings. Also, mounting a GPS on a truck or all-terrain vehicle can reduce the time needed to create terrain data to validate the airborne technologies and as-built conditions following construction.

Efficient Operations and Maintenance Mapping Technologies

The use of ground-based laser or high-definition scanners is also being considered for capturing as-built information on power plants and existing transmission lines. This high-fidelity information will assist the operations managers in understanding the current condition of the objects being surveyed. Presently, helicopter-borne sensors are combining LiDAR, digital photography, weather monitors and high-resolution video to gather data in a single pass over an existing power line. Unlike a fixed-wing aircraft, helicopters can fly “low and slow” to literally saturate above-ground objects such as conductors, towers and vertical obstructions with LiDAR pulses and thus capture high-resolution imagery.

This fusion of LiDAR elevations and color digital aerial photography shows power line structures and power lines. Danger areas that are encroaching on the power line right-of-way are shown in red.

LiDAR and digital photography can also be used to detect whether vegetation and urban development are encroaching on an existing power line. The same type of data is very useful during power load modeling as engineers try to determine whether more energy can be moved through a given power line and whether the new line sag is located too close to vegetation or man-made objects, which will create danger areas.

A Powerful Future

The American Recovery and Reinvestment Act stimulus package will push out approximately $32 billion in funding for transmission line upgrades, the smart grid and renewable power transmission. These types of initiatives to improve energy availability and renewability are creating numerous opportunities for surveyors and mappers in the United States and worldwide. The integration of multiple sensors on a single airborne platform offers a plethora of data that--when fused geometrically and relationally--can provide solutions to environmental, planning, engineering and social challenges. The ability of surveying and mapping professionals to provide innovative solutions to the many complicated issues associated with the life cycle of completing a corridor project will offer both short-term and long-term rewards.

Sidebar: Powerful Technologies

The Western Area Power Administration (Western) markets and delivers hydroelectric power and related services within a 15-state region of the central and western United States. In its efforts to define future power transmission corridors and maintain existing power lines, Western relies on aerial surveys to obtain planimetric, topographic and other thematic data such as wetland delineation. To produce these databases, Western requires surveyed ground control, surveyed line crossing data, airborne LiDAR, digital aerial photography and color infrared photography.

The advances being made in surveying and mapping technologies fit Western’s mission to create engineering solutions that combine sound business practices and cost containment. When Western selected Merrick & Company to serve as the mapping consultant on a recent project, the firm combined multiple sensor technologies on one fixed-wing aircraft to efficiently create the databases required to design a new transmission line. The technologies included a Leica ALS50 Phase II+ LiDAR system with multi-pulse-in-air (MPiA) capability, Merrick’s proprietary Digital Airborne Camera System (DACS), an orientation system that included a micro intertial reference system (IRS)/inertial measurement unit (IMU) and a Novatel OEM airborne GPS device, an AISA Eagle VNIR hyperspectral sensor, and a variety of weather monitoring equipment.

The LiDAR system was used to create the high-fidelity digital elevation model used for drainage studies, access-road design, tower height analysis and line sag modeling. It also defined catenaries of existing transmission lines and distribution lines that crossed the new line.

Color digital aerial photography and photogrammetry were used to produce vector databases. This information was rectified using the LiDAR elevations, GPS, and IMU data to create a digital orthophotograph--an aerial photograph that is free of displacement and distortion and allows for precise measurements and interpretation.

The orientation systems of a GPS and IMU were used to provide real-world coordinates of the position and attitude (tip, tilt, yaw and crab) of the aircraft as well as the coordinate values for LiDAR point and photo centers. “Using LiDAR has helped streamline the way we site transmission lines by eliminating the need to acquire rights of entry to survey potential routes,” said Randy Wilkerson, a public affairs specialist with Western.

The hyperspectral sensor produced a digital picture comprising 128 discrete images over a broad range of the light spectrum referred to as a datacube, which stores information about discrete remotely sensed objects such as vegetation. The vast amount of information stored in each pixel of a hyperspectral datacube allowed remote sensing scientists using sophisticated software to separate the data into discrete land-cover classifications such as wetlands, endangered plant species and animal habitat. These classifications are possible because each object on Earth has a fairly unique spectral signature. Below is an example of wetland determination along a proposed power line using image processing techniques from hyperspectral data. Such capabilities allow environmental problems to be mitigated quickly and effectively.

GPS surveying techniques were also deployed throughout the project. First, the geodesist created the control network plan. Next, base station control positions were surveyed so that the airborne sensor data could be “tied” to real-world coordinates. Elevations were then surveyed in a variety of land use and land cover locations to validate the LiDAR ground and line crossing data. And finally, power pole legs and points of intersection (PIs) along a transmission line were surveyed and staked for final design.

In the past, multiple aircraft mobilizations and numerous ground control points would have been needed to gather the amount of data that is now collected with co-mounted sensors on one aircraft and minimal ground survey work. Western’s objective is to create power transmission opportunities for both traditional and alternative sources of energy in the most cost-effective and environmentally sound manner. Modern remote sensing technologies provide the opportunity to achieve both goals.

“At Western, we’re always looking at new technologies to improve how we go about our business and to become more efficient,” Wilkerson says.

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