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LIDAR OPERATING PRINCIPLES / DATA ACQUISITION

Image Illustrating Lidar Operating Principles

Lidar First and Last Return

While reflecting from objects such as tree canopy and structures, the Lidar pulse also finds the edges of and gaps and holes in objects (i.e., between the foliage of trees) to reach the ground. These Lidar returns are reflected back to the aircraft-mounted sensor where they create an accurate and valuable dataset. The first Lidar return reflects the highest elevations of ground features such as tree canopy, buildings, power lines, etc. The last Lidar return reflects the ground level, from which a bald-earth dataset can be extracted. The bare earth dataset provides accurate data on the elevation and features on the surface of the earth.

The images to the right illustrate first return data (top) and a last return data Digital Elevation Model (bottom). The dark areas in the first return image represent vegetation and/or structures which obscure the ability to view the elevation characteristics of the terrain. When first return data is removed from the image, the terrain and elevation data can be viewed as a bare earth DEM.

Lidar First Return Data

Lidar Last Return Data / DEM (Digital Elevation Model)

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LIDAR OPERATING PRINCIPLES

Aerial Lidar (Light Detection and Ranging) is an aerial mapping technology which uses reflected laser returns—from the earth’s surface to an aircraft with on-board GPS and IMU sensors—in order to determine the precise elevation and geospatial location of terrestrial objects and features. After careful review, the acquired Lidar data is processed by a team of Sanborn Lidar professionals to generate a "Lidar point cloud." From this data, DEMs and other valuable Lidar products can be created for a variety of uses. With innovations such as multiple intensity returns and increased pulse repetition rates, Lidar is an accurate and effective method for creating three-dimensional topographical aerial maps and highly accurate surveys of both surface terrain elements and manmade structures.

Aerial Lidar Scanner (1)

Sends/receives up to four returns per pulse using a laser transceiver, receiver and scanner with variable frequency range.

IMU (2)
(Inertial Measurement Unit)

Measures attitude (pitch/yaw/roll) of aircraft every .002 second.

Aerial GPS (3)
(Global Positioning System)

Based on GPS satellite triangulation, measures the location of the aircraft every 0.5 second.

Ground GPS (4)

Measures the location of the aircraft every 0.5 second relative to a known ground position.

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