Beam Setup - Gemini 620pd Profiling Product Manual

Gemini Software Operation
Absorption
As sound from the Gemini Profiler transmitter travels through the water, the
amplitude of the received reflected sound pulse reduces over range due to absorption
and spreading losses. The Gemini Profiler compensates for these losses by applying
a time varying gain curve to the received signal such that the measured reflectivity
of a target is not dependent on the range at which the that target is viewed.
The absorption loss coefficient (between 70 and 200 dB km
Gemini Profiler can correctly compensate for the absorption losses. The absorption
loss coefficient will vary depending on the temperature and salinity of the water, and
should be given at the acoustic frequency of 620kHz.

12.4.8. Beam Setup

The Beam Setup options allow control of the sector which is scanned by the Gemini
sonar, this can be useful if the area of interest is quite narrow, such a a pipe trench.
To vary the start and end of the scan sector simply drag the sliders sideways or use
the + and - buttons to increment the values one step at a time. The maximum range
is from -65° to +65°.
The Spacing option allows configuration of the beam spacing:
• Equidistant beams are arranged so that they intersect a flat sea floor at equal
distances apart (more beams at the edges of the image than in the centre).
• Equiangular the beams are spaced with an equal angle between them.
• Inverse Sinusoid is the Gemini default and concentrates more beams in the
centre of the image.
• Fixed (Low Bandwidth) useful only for very low bandwidth systems, will
disable some of the configuration options.
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Note
The Scan Sector can also be adjusted using the handles on the scan display,
or using the keyboard shortcuts 'b' and 'g'.
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Gemini Profiling System
), must be set so that the
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