Chapter 6 — Exam Question 7

What are the key performance characteristics of ALS, and what are the major differences
with airborne microwave radar?

Answer

•

ALS can operate day and night;

•

can operate under the cloud ceiling (flying height as low as 50 m);

•

can operate on helicopter or fixed wing aircraft;

•

penetrates vegetation;

•

does not depend on terrain texture;

•

yields dense data: 1 point per 0.5 to 4 m

2

;

•

yields high point accuracy: 10-30 cm;

•

all digital data acquisition, no ground control, and fast data processing.

There are two major advantages of laser ranging compared to microwave radar:
high energy pulses can be generated in short intervals and highly directional
light rays can be emitted. The latter is possible because of the short wavelength
of lasers (10,000 to 1,000,000 times shorter than microwave). The consequence
is higher ranging accuracy. Another consequence is that the laser can ‘see’ very
small objects (e.g. powerlines) and it offers a better point definition.

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