Areas of Application

- Topographic terrain surveying including forest areas
- Vegetation height measurements
- Surveying of mudflats and coastlines
- Flood plain mapping
- Surveying and monitoring of glaciers
- Creation of city models for telecommunication network planning and noise control
- Planning of road, railway, pipe and cable routes
- surveillance and monitoring of high tension overhead cables
- Volume control of open pit mines and refuse dumps

Products

Digital elevation models in various grid intervals:

- of the surface of the earth
- of ground objects e.g. city models, vegetation models
- Perspective views e.g. gridded mesh net and gray shade perspective images
- Height profiles
- Elevation grids, contour lines and contour maps
- Derivation of secondary maps
- Slope and aspect maps

Since the introduction of Laser Mapping Hansa Luftbild and TopScan have captured over 100,000 km² of data for terrain surveys, for city, water, sea transportation, and coastal conservation authorities, and processed and analysed the data with geoinformation systems.

The Function

The laser scanner is installed in an opening in the floor of the aircraft. The device pulses at regular intervals a laser beam, which is bounced back by the earth’s surface and objects on the earth’s surface. The time difference between transmission of the beam and its reflection is measured. The laser beam is pulsed by a high speed rotating mirror (scanner). This refracts the laser beams across the flight path so that a wide swath of measurement points can be covered.

Using a combination of the forward motion of the aircraft, and the oscillation of the mirrors a track which approximates a zigzag is formed along the points of reflection.

The set-up of the scanner and flight parameters such as scanning angle, frequency, flight speed and height is dependent on the usage planned for the elevation data. The density of points can be modified by varying data capture rate. Terrain sampling can be controlled by altering flight speed parameters, and the scanning angle and rate. The distance between the laser device and the earth’s surface is calculated by measurement of the elapsed time between emitted and returning signals. The values are saved on data storage mediums.

The aircraft’s position is determined by highly accurate, differential GPS measurements. A high accuracy is attained by determining aircraft position with an in-flight GPS and a ground based GPS reference station.

During flight an inertia platform (gyroscope stabilised system) determines and stores the aircraft movement in three axes; in other words the three angles which define the deviation of the aircraft from north and the perpendicular. The correct position and height of each measured point is calculated following the flight mission using the synchronised recorded data for distance, position, orientation and the co-ordinates of the ground reference station.

The Airborne Laser Terrain Mapper ALTM 2050 and ALTM 1225 which are being used by Hansa Luftbild in co-operation with TopScan were developed by the Canadian firm Optech.

The concept of combining a highly productive laser with a mechanically manipulated mirror has proven its worth. A high pulse rate, variable angle scans, and a relatively high flight altitude by comparison with other laser scanning systems combined with a faster flight speed ensures an optimal fit between individual requirements and cost considerations.
In addition flights can be made at night, flying is not limited to the daytime.

A marked advantage of laser scanning is the capture of precise height data from forest floors. Experience has shown that in most wooded areas the forest canopy has numerous small gaps, a high percentage of which can be penetrated by laser, to the forest floor. Due to this factor data can be captured from both the forest floor and canopy and thus the volume of vegetation calculated.

Relevant elevation data is filtered with the assistance of various algorithms from the irregular grid pattern formed by the reflected laser signals.

The Systems

Technical Specifications:

ALTM 3100

laser pulse rate: 100.000 Hz
pulse operation: 4 pulses
scan angle: to +/- 25 deg
operating altitude: 80 - 3.500 m
digital camera 4092x4079 pixel
pixel size 0,009 mm

ALTM 2050

laser pulse rate 50,000 Hz
pulse operation: first / last / both
scan angle: to +/- 20 deg
max. operating altitude: 2,000 m
digital camera 4029x4079 pixel
pixel size 0,009 mm

At an altitude of 1,000 m a laser beam has a diameter of approximately 25cm. In its path to the earth’s surface the beam can repeatedly encounter other objects e.g. foliage and be reflected by them. The ALTM laser scanner can differentiate between these multiple reflections. The first or last reflected signal can be selected and recorded. Selection of the first signal often corresponds to foliage rather than the earth’s surface, while the last reflected signal can with high probability be predicted to correspond to the terrain. The recording mode can be adjusted - according to the desired end application – to capture the earth’s terrain (last reflected signal), and/or to capture the surface of objects (first reflected signal).

The ALTMs have an integrated video camera which optically records a flight path during daytime operation. In the ALTM 2050 a digital camera for Color or CIR mode is integrated beside the inertial unit for direct geo referencing. From the simultaneous admission of halftone images, elevator information and orientation parameters can be provided fast and efficiently orthophotos for many GIS and Mapping applications.