Airborne Laser Scanning – Cost effective spatial data

Airborne Laser Scanning – Cost effective spatial data

David Turton
Manager – Aam Geoscan
Email: D.Turton@aamgeoscan.com.au

David Jonas
Production Manager, Aam Geoscan
Email: D.Jonas@aamgeoscan.com.au

AAM GEOSCAN, A Division of AAM Surveys Pty Ltd.
11 Wicklow Street, Kangaroo Point Qld. 4169 Australia
Tel: +61738911033, Fax +61738911050

Technical Description of ALS
An ALS system consists of three components:

A Global Positioning System (GPS) to position the moving aircraft in space.
An Inertial Measurement Unit (IMU) to record the aircraft attitude and acceleration.
A laser light source which directs a stream of discrete laser points towards the ground at approximately ninety degrees to the line of flight. The time taken for each of these discrete points to return to the aircraft is accurately recorded.

In addition, a ground based GPS unit is required to be operating within 20km to 50 km of the survey area, depending on survey accuracy required. The coordinates of this base must be known. Data from the station is used to compute a differential GPS solution for the aircraft.

The system components are shown diagrammatically below.

Depending on the ALS manufacturer at least two recordings of each of the laser points emitted are stored by the system. These include the first return received and the last return received. The first return may be from the top of a tree while the last may represent the ground beneath the tree. Coordinates are computed for both the first and last returns.

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