Petroleum and utility companies need precise knowledge of the topography when planning the construction of pipelines, utility routes or the mapping of broad area exploration sites. Accurate terrain measurements are critical to assess the feasibility of construction in a wide variety of terrains such as valleys, plains with undulations, heavily wooded terrain, deserts, mountains, hills, rocky terrain or areas with marshes, bodies of water such as ponds, streams or rivers.

Airborne lidar and digital imagery are ideal technologies for the rapid and accurate acquisition of survey data for route location and broad area mapping. A fast and reliable airborne method of obtaining 3-dimensional data for the creation of a Digital Terrain Model, LIDAR (LIght Detection And Ranging) integrated with a digital frame cameras digital color images provides a full evaluation of ground characteristics.

LIDAR data sets have become an integral component in the planning and design process when conducting bare-earth assessments, risk-management studies and right-of-way surveys. LIDAR measurements can reveal minute details such as tree height and distance from the canopy to the ground, shows minor undulations in relatively flat terrain and allows rapid, cost-effective, accurate mapping of linear corridors.

Since 1997, Lasermap of Montreal Canada has been a leader in LIDAR surveys conducting numerous terrain model projects for route locations and geophysical exploration. Digital terrain models produced using this technology have been used for detailed planning and engineering projects, often saving tens of thousands of dollars compared to traditional techniques.

Lasermaps Optech 2050 system, one of the most reliable and accurate lidar systems available, is capable of producing a DTM to an accuracy of +/- 15cms (6 inches), with point to point accuracies even better. The system is extremely useful for applications where a high degree of accuracy and speed are necessary, or where accessibility is difficult. A detailed DTM can be produced by lidar in a much shorter time frame than a similar product using any other technology. Their careful attention to quality control and proper calibration, sufficient data can be collected to produce 0.3 meter (one foot) contours.

Using positioning from a Global Positioning System and the attitude (tilts and tips) recorded by the Inertial Measurement Unit, a precise 3D coordinate position can be determined for each pulse. Because of the active nature of the sensor and its ability to penetrate between a lot of vegetation, lidar surveys can be conducted when other technologies are not suitable or are impractical. (For example it is not necessary to wait for leaf-off conditions.)

Lasermaps system emits energy pulses at frequencies of up to 50,000 Hertz - that is 50,000 times per second. These pulses are reflected off the ground, vegetation or man-made structures at different time intervals, allowing the distances between emission and reception to be calculated. Using these distances, along with the attitude of the laser (from the inertial system) and its position (from the GPS), the position and elevation of each spot can be calculated. With the high pulse emission rates, the laser can obtain as many as 3,000,000 3-D points per minute. Depending on the flying height, the aircraft speed, and the frequency and width of the laser scan, the ground point density can be as close as 0.5 meter (2 feet).

As well, the digital camera system operating on standard color wavelengths is ideal for corridor applications. With imagery, an aerial record of the ground can indicate land use and any obstacles to construction. Along existing rights of way it can be used to show vegetation growth and intrusions. The pixel size acquired by the camera varies depending on flying height from 9 inches to 2 feet (20-50 cms). Because of the low flying height and active aspects of the laser system, the unit can often be flown below clouds when other airborne sensors are not effective, or at night. (Color imagery, of course, requires daylight, but intensity imagery does not.)

If you would like to learn more about aerial Lidar, how it can benefit your spatial information needs, or just for general information, please feel free to contact us. Visit our web site at www.spatialresources.com, email us at info@spatialresources.com or call 720-934-2482.

Until next time...

Cheers!

Roland Mangold