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light pulse is measured. For small distances, one sometimes uses
ultrasonic time-of-flight methods, and the device may contain a laser
pointer just for getting the right direction, but not for the distance
measurement itself.

 Frequency modulation methods involve frequency-modulated
laser beams, for example with a repetitive linear frequency ramp. The
distance to be measured can be translated into a frequency offset,

which may be measured via a beat note of the sent-out and received
beam.
 Interferometers allow distance measurements with an accuracy
which is far better than the wavelength of the light used.

A laser radar is a device which uses one of the distance
measurement techniques as described above, and scans the direction
of the distance measurement in two dimensions. This allows the

acquisition of an image, or more precisely a depth profile of some
object, as required e.g. in robotics. For acquiring such depth profiles at
a higher rate, there are sensor chips similar to CCDs (charge-coupled

devices) with internal electronics to detect phase shifts, so that the
distance for each pixel can be measured simultaneously. This allows
rapid three-dimensional imaging with very compact devices.

Compared with ultrasonic or radio and microwave frequency
devices (radar), the main advantage of laser distance measurement
techniques is that laser light has a much smaller wavelength, allowing
one to send out a much more concentrated probe beam and thus to

achieve a higher transverse spatial resolution. Another advantage, that
an optical bandpass filter makes it possible to very effectively remove
noise influences at other optical frequencies.

VI. INDIVIDUAL WORK

Task 1. Find a sentence in each paragraph which gives the
definition of the surveying equipment. What is this

instrument used for?

ELEMENTARY SURVEYING EQUIPMENT

Chains or tapes are used to measure distances on the field. A
chain (see Figure 11.2.) is made up of connected steel segments, or
links, which each measure 20 cm. Sometimes a special joint or a tally
marker is attached every 5 metres. Usually, a chain has a total length

of 20 metres, including one handle at each end.

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