User's Manual

www.malags.com
32
9 Trigger devices
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The most efficient method of data acquisition is to use a
distance-measuring wheel or profile encoder (hip chain) to
control the collection of radar data. Data is acquired at user
defined distance intervals so that the position of each trace
along a survey line is given by the position of a radar trace in
the data file. This simplifies data acquisition procedures and
locating the position of reflections.
The hip chain can be used when scanning from a sled or
when the transmitter and receiver are mounted on the carrying
handles. The hip chain comes with cotton string of a length of
2800 meters in a roll. The string is made of pure cotton that
decomposes in nature. Its greatest advantage is in trackless
and undulating terrain where it would be impractical to use a
measuring wheel.
The measuring wheel may be more appropriate to use for
distance control for surveys on flat terrain or in urban areas (on
Skid Box or shielded antennas). The measuring wheel is
attached to the tow handle of the skid box or directly on the
shielded antennas. The measuring wheel for Skid boxes
operates through a rubber band (models 9610-) that circles the
pulse encoder. In wet or snowy terrain it is important that the
rubber band and the wheels are kept clean in order to let the
band run free.
All distance-measuring devices for the RAMAC/GPR use an
optical encoder that transmits electrical pulses to the CUII. A
distance calibration file is used to convert the number of pulses
to the correct distances. The operator can create calibration
files or use those supplied with the installation diskette.
These calibration files for different length encoders contain