Laser scanning

A pioneer in the operational use of laser scanning, TerraImaging was one of the first companies in Europe to use an Optech ALTM sensor and has been working with Lidar technology since 1994. Mounted in an airplane or helicopter, we use a variety of scanner systems (Optech ALTM 1020, 1225, 3033, and 2050, 3100 and Gemini), with integrated 4k x 4k and 4k x 5k digital cameras. With up to 150,000 measurements per second, the Gemini is the latest and most efficient sensor for high-end needs. With this variety of different systems, TerraImaging can quickly and efficiently provide clients with the required data products with or without simultaneous acquisition of digital image data. Point densities and accuracies can be adapted to the client's application and range from one point per m² and 5-10 cm accuracies for data acquired with airplanes, up to high resolution surface models with tens of points per m² and better than 5 cm accuracies when using a helicopter platform. Simultaneously acquired image data can have resolutions as high as 3 cm for helicopter and 7.5 cm for fixed wing flights.

How It Works:

Mounted in an airplane or helicopter, the sensor emits laser pulses at a very high repetition rate of tens of thousands of measurements per second, each of which hits the target surface and reflects a small portion of its energy back to the sensor. A receiver in the sensor detects this reflectance from the earth's surface or from objects on the surface. The on-board computer records the difference in time between the emission of the laser pulse and the reception of the reflected signal, as well as the intensity or strength of the return signal. The distance between the plane and the point on the earth's surface is calculated from the time the laser pulse took to return to the plane, after emission from the sensor and reflection by the point on the earth's surface. A rotating or oscillating mirror in the sensor independently scans the pointing direction of the sensor across the flight path of the platform, providing a range of measurements perpendicular to the direction of flight. This greatly improves the area collection efficiencies of the sensor.

However, the range to the measured point alone is not sufficient to create accurate data. The direction of the laser pulse and the position of the scanner system at the moment of each measurement must also be recorded. To achieve this, the attitude of the laser scanner and its orientation in space is measured by an Inertial Navigation System (INS), while the laser scanner system records the direction of the laser pulse in reference to the laser scanner (the pointing direction of the sensor). Simultaneously, the position of the scanner system and its location in space is determined by dGPS.

Through combining all the different data, range to target, orientation and location in space, it is possible to calculate the precise co-ordinates of every single point in absolute x, y and z co-ordinates. Multiple returns, including the return from the ground (last pulse) enable the computation of a bare ground model (Digital Terrain Model) and the Digital Surface Model. Using a combination of custom and off-the-shelf software, the location, classification, attributes and properties of objects can then automatically be identified and determined, especially with the additional use of any simultaneously recorded intensity data and digital image information.

TerraImaging laser scanning (Lidar) products are currently being used in:

• Production of nationwide/statewide elevation models
• Determination and mapping of dikes, dams and other infrastructure facilities
• Risk management for disaster managers
• Coastal zone management
• Detection of change and alteration of topographic data sets
• 3D city noise models, urban planning or microclimate studies
• River and flood plain models
• Planning of telecommunication networks or facilities
• Forestry management