Chapter 6 — Exam Question 6

What are the components of an airborne laser scanning system, and what are the opera-
tional aspects to consider in planning and executing an ALS mission?

Answer

An ALS system consists of the actual scanner (complete with laser source, pho-
todiode, scanning mirror, etc.), as well as a platform (aircraft or helicopter), a
differential GPS, an Inertial Measuring Unit (IMU), data recording units, and
software.

A number of aspects need to be considered before an ALS survey can be

carried out: (i) the appropriate scanner system must be chosen, in terms of laser
colour, pulse frequency, scan rate, first- and last-return detection capability, etc.
The platform chosen determines the possible groundspeed and flying height
and, therefore, influences the resolution of the survey. Flight planning needs
to be done using adequate software and elevation data in the case of mountai-
nous terrain. A calibration site must be established and the GPS ground stations
be selected/surveyed, and the logistics of operating them have to be defined.
Before take-off, the IMU must be initialized and the system calibrated if it was
newly mounted in the aircraft.

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