Airborne LIDAR Surveys - An Economic Technology for Terrain Data Acquisition
Dr. Réjean Simard
Lasermap Asia Sdn. Bhd.
Suite 2M, 2nd Floor, 2330 Century Square, Jalan Usahawan
63000 Cyberjaya, Selangor D.E., Malaysia
Tel : +603 8318 0052, Fax: +603 8318 0049
Email: rejean@lasermap.com
Web: www.lasermap.com
Mr. Pierre Belanger
GPR Consultants Inc. / Lasermap Image Plus
85 chemin Grande Côte
Boisbriand, Quebec, Canada, J7G 1C4
Tel : +1 450 437 2922, Fax : +1 450 437 2923
Email: pierreb@lasermap.com
Mr. Mohamed Razali Mohamed
Malsat Sdn. Bhd.
No. 29-3 Jalan USJ 21/1
47630 UEP Subang Jaya, Selangor D.E., Malaysia
Tel: +603 8023 3751, Fax: +603 8023 3752
Email: mohamed_razali@hotmail.com
Ir. Dr. Mohd Asbi Othman
Mohd Asbi & Associates Sdn. Bhd.
B-3-15, Megan Phileo Avenue
12, Jalan Yap Kwan Seng
50450 Kuala Lumpur, Malaysia
Tel: +603 2166 8200, Fax: +603 2166 5355
Email: asbi@asbi-associates.com.my
Introduction
This presentation is to provide a brief introduction to airborne LiDAR technology, show some samples of what sort of products can be developed and for which applications, and finally to review a project completed in Malaysia in the year 2002 for landslide risk assessment in rugged terrain in Sabah.
LIDAR Technology
Airborne LiDAR systems are composed of three separate technologies: a laser scanner, an Inertial Measurement Unit (IMU) and a Global Positioning System (GPS) all configured together with a computer system which ensures that all of the data collected are correlated with the same time stamp - this is extremely important as all of the components require extremely accurate timing (to the millisecond).
The components for LiDAR technology have been around for many years. Lasers were invented in 1958. Inertial technology has been around for a long time and GPS has been around commercially for over 15 years. The challenges faced by user of LiDAR technology is putting all of these technology-components together and making them work together – at the same time ensuring that it is small enough for use in an aircraft or helicopter. In reality this has only been achieved commercially in the last eight years or so.
The major limiting factor for the technology has always been (and still is) the airborne GPS and it is only in the last ten years that GPS systems have become accurate enough to provide airborne positions better than 10cm.
Airborne laser profiling has been around for much longer, but the absolute position of the aircraft was always very difficult to determine without a sophisticated GPS. Continued research over the last five years has meant that LiDAR systems (especially those made by the main manufacturers) have become quite robust and very dependable. Individual units still seem to have quirks and many older units were somewhat less than reliable, and like everything else in life, you get what you pay for.
With respect to the use of a GPS on board the aircraft, it is necessary to provide a link to a ground GPS station on a known control point. The ground station should be located on or close to the project site - where the aircraft is flying. This is to ensure that the aircraft record the same satellites signal as the ground station. If the ground station is located further away from the aircraft or project site then it is quite possible some of the satellites recorded by the ground station will be different from those recorded by the aircraft GPS. There are a number of other reasons also: absolute accuracy tends to diminish the further away the aircraft is from the ground station. There are several causes for this, some of them relate to atmospheric conditions, curvature of the earth, geoids and spheroid separations (the spheroid for the map projection is not based on the same centre of the earth as the satellite orbit) etc.