Power Line Detection and Lidar Sensor Limits
By Matt Bethel, Manager of Systems Engineering, Merrick and Company, and Michael Sitar, Airborne Survey Products Manager, Optech InCorporated
Acquiring lidar data from power lines using a helicopter-based platform is a growing market. To be successful in this market the lidar solution must have exceptional line detection and measurement capabilities. Line detectability is critical for two reasons: accurate modeling and ancillary information collection. In both areas, Optech’s ALTM Orion C200 corridor mapper has demonstrated an impressive ability to capture information in remarkable detail.
To adequately model the power line network, the lidar must be able to detect laser returns from the surface of the wires. The greater the number of laser returns from the catenaries, the better the results of running automated processes to extract power line features such as transmission lines, static wires, attachment points, towers, and so on. Power line features can vary significantly in material, diameter, and coating, and these variations can cause dropouts (missing lidar points) that result in data voids. Depending on the system, these data voids can be substantial—to where there are not enough points to properly model power line features.
In some lidar systems, detectability can be adjusted to reduce the dropout rate, but doing so can compromise the system’s vertical accuracy. As the system’s gain ratio is increased to improve detection of small targets, large targets can saturate the receiver electronics and create vertical height uncertainty. Therefore, selecting and calibrating the appropriate lidar system solution is critical to successfully delivering a quality data product. The Optech Orion C200 has proven to yield exceptional line detectability and consistent vertical accuracy across all types of features, large and small.
Along with modeling data, surveyors are often required to collect ancillary information from lines or features that are much smaller than the diameter of the main transmission line (static wires, distribution lines, cable TV lines, telephone lines, fences, etc.). Any feature that crosses above or below the main transmission line is expected to be collected by some means. If the lidar system cannot detect these features, ground survey crews must be sent to do so. Apart from the added cost, there are also safety concerns, plus delays for obtaining permission to access survey properties.
Being able to detect and collect all these features with a single pass from a lidar system saves untold time and money. Furthermore, rather than prolonging the data collection over several months, it ensures that all features are captured at one time, thus allowing for identification, construction or removal of planimetric features from one comprehensive data set.
Wire Detection Test
To demonstrate the performance potential of the Optech Orion C200, Merrick and Company constructed a wire detectability test site using wires of varying thicknesses, coatings and non-coatings (figures 1 and 2). The test was flown using different parameters such as altitude, laser pulse rate, and scanner settings. Merrick was impressed to find that all test flight settings yielded adequate to exceptional wire detectability, with many lidar points recorded to allow for accurate modeling of every wire—even the thinnest.
Fishing Line Test
Pleased with these results, Merrick decided to push the detection limits of the Orion C200 even further. The smallest wire detected in the original test was a 1-mm speaker wire, so they then decided to use transparent, monofilament fishing line. Fishing lines of varying thicknesses were set up at the airport, then flown over. In post-analysis, Merrick was amazed to find that the Orion C200 detected all the lines.
“We flew over these lines during a scheduled calibration flight and were pleasantly surprised to see that the lidar detected all weights of fishing line,” said Matt Bethel, manager of systems engineering for Merrick. “Understandably, we would not claim that the fishing lines were ‘modelable,’ but the sensor did record multiple shots for every line weight, ranging from 12 lb. to 50 lb. Our final test conclusions showed that the smallest diameter that we can reliably detect and model accurately was a 1-mm single-strand speaker wire. The Orion C200’s exceptional detectability gives us great confidence in what we can commit to deliver to our end-users.”
Lidar Imaging Solutions
Optech is the world leader in the development and manufacture of advanced laser and imaging survey instruments. With operations and staff worldwide, for over 35 years Optech has refined lidar technology to empower surveyors with fast, accurate, and cost-effective solutions.
Optech’s Airborne Survey products excel in the efficient acquisition of high-accuracy spatial data over land and water. Optech’s ALTMTM and CZMIL systems provide the competitive advantage that clients demand. Available in both application and platform-dependent configurations, Optech ALTMs offer the greatest flexibility and efficiency available to the professional surveyor today—and with a complete line of fully integrated aerial imaging cameras. Whether it is a high-altitude wide-area mapping project, a low-altitude power line survey, or a small payload, low-power platform requirement, Optech delivers complete data collection solutions for a full range of application and installation scenarios.
CZMIL is an integrated lidar-imagery sensor system and software suite designed for the highly automated generation of physical and environmental information products for mapping the coastal zone. With its enlarged aperture receiver (4 times the size of previous sensors) and doubled spatial resolution, CZMIL accelerates data and product delivery and improves the quality of information derived from fused lidar and imagery data sets.
Optech’s airborne digital cameras, either standalone or integrated with a lidar, are wide-ranging: large- and medium-format, patented True Forward Motion Compensation, and electro-optical, infrared and multispectral imaging systems. Ruggedized, high-precision metric imaging systems provide camera control, inertial navigation system integration, and image processing capabilities, enabling single and multi-sensor solutions that combine visible, multispectral and infrared modules into integrated payloads.
Optech’s Lynx Mobile MapperTM represents the next generation in the rapid collection of survey-grade 3D data. This revolutionary mobile mapping system integrates the latest innovations in lidar sensors with best-of-class imaging, navigation, and product warranty and support.
Optech’s ILRIS (Intelligent Laser Ranging and Imaging System) is a complete, fully portable, laser-based 3D imaging and digitizing system for the commercial survey, engineering, mining, and industrial markets.
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