R2Sonic 2022, Руководство по эксплуатации

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Page 94 of 133
Version 3.0 Rev r000
Date 25-08-2010
Part No. 96000001
10.2 Measuring Offsets
The accurate measurement of offsets is vital to the accuracy of the survey data. If possible, the
vessel will be put on a hard stand so that it can be very accurately measured using standard land
survey equipment, such as a total station. However, this may not be possible and the offsets will
have to be measured using a tape and plumb-bob, which is detailed below.
10.2.1 Sonic 2024 Acoustic Centre
Please refer to the drawings on Page 104 to 106 to obtain measurements, with reference to the
system offsets, when mounting on the Sonic mounting frame.
Figure 80: Sonic 2024/2022 Acoustic Centre
10.2.2 Horizontal Measurement
All measurements should be made with a metal tape measure. A cloth tape can stretch, it can also
be knotted or kinked, unknown to the persons making the measurements. At a minimum, two
people should be assigned to take the measurements; three people will work better with the third
person writing down the measurements. One person will be the holder and the other will be the
reader. Starting at either the reference point or the sensor, the distance will be measured. When
either the reference point or the sensor is reached, the two people will reverse roles: the holder is
now the reader and the reader is the holder, the transverse is made back to the point of beginning,
but not using the same path. If reference marks were made on the first leg, they should not be used
on the second leg back. If the measurement from the sensor to the reference point, in one direction,
agrees with the measurement in the opposite direction, made by a different reader and holder, then
the offset is good. If there is a small disagreement in measurements, the two measurements can be
averaged. If there is a large disagreement then the process should be repeated. What is a small
disagreement? A few centimetres can be expected.
10.2.3 Vertical Measurement
To measure elevations or the Z offset, the use of a plumb bob is required. This can be something as
simple as a spanner tied to a length of line and lowered from one deck to the next. The plumb bob
will also allow for accurate measurements in the X and Y direction when transposing them from one
deck to the other.