- Refurbishment - lifespan of towers and hardware replacement
Assessment of these and other issues is ongoing. Ignoring any one of these issues can be very costly.
LIDAR has become a valuable tool to the electrical utility sector in that it replaces many traditional survey methods with a single data source. Processed LIDAR data enables the measurement of catenary clearances and ground DEMs and the classification of vegetation, tower and wire distributions. When coupled with video and photos acquired from the same airborne platform, a complete inventory of terrain types, hardware conditions and corridor access points can be constructed to create a comprehensive dataset which can be integrated into CAD, GIS and PLS-CAD packages for mapping, modeling and reference databases.
The technologies utilized to acquire this detailed dataset require an integrated instrument suite flown from an airborne platform. These technologies are briefly explained below.
LIDAR Technologies
To master the task of collecting vast corridors of terrain data, airborne LIDAR "LIght Detection And Ranging" systems have been developed for acquiring data for route selection and for asset management of existing transmission networks. This technology utilizes a laser to accurately measure distances. The laser is only one element of the LIDAR system, however. LIDAR requires a suite of support instruments, most of which are used to establish position and orientation of the laser with the point being sampled on the ground.
The main components used in LIDAR systems include:
- Positioning system (GPS/IMU)
- Laser ranging system
Position information is vital to the definition of accurate X, Y and Z attributes of the terrain and transmission corridor data. Typically, LIDAR is flown from either a fixed wing aircraft or helicopter. Differential GPS is used to obtain aircraft positional accuracies ranging from 0.05 -0.2m. This defines the platform position. The platform is, however, experiencing pitch, roll and yaw due to aircraft motion. This motion affects the orientation of the laser pulse. These angular translations are measured by an Inertial Measurement Unit (IMU). Also encoded into the data is a time stamp from a high precision clock.
The laser used in many LIDAR systems sweeps through an angle range acquiring a swath scan of data points. Typical sample intervals for the laser pulses range from 5-30KHz.
Imagery Technologies
As LIDAR records only reflected hits of the terrain and transmission lines, imagery is essential to fill in the visual detail of the surveyed area. This visual data can be used by repair crews, for example, to determine what kinds of equipment to take to a site, the scale of the repair and the nearest access point to the site.
During the acquisition of LIDAR data, low-cost high-quality imagery sources such as video and digital stills can be logged and encoded with position and time stamps common to the acquired LIDAR data.
Apart from having a visual record of the entire survey line on tape, video imagery can be captured by computer and displayed onto a PC. By running a calibration routine the display's co-ordinate system an be geometrically corrected and transposed into a mapping coordinate system thereby enabling the position of attachment points or any number of attributes about the lines, the vegetation and the land use of the surveyed corridor to be mapped.
Digital stills afford much higher resolution of the surveyed corridor and can be rectified and stitched together to create orthomosaics of areas of interest. These images often serve as base maps for the layering of GIS data.
Integrated LIDAR and imagery systems offer cost-saving, comprehensive surveys and flexibility of data use for the electrical utility sector. The hard copy maps, digital data and video generated from a single pass provide accurate detail to populate GIS and CAD systems and provide the information needed by those responsible for managing transmission networks.
Robert Iantria is with Terra Remote Sensing Inc.
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