SonarMite DFX v1.20 (c) Lymtech 2016
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Range and Bearing from hand held laser plus Tide plus Time
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Simple event marking past known position markers
The basis on which all data correlation is achieved is internal time base, so particularly when
using the SonarMite with GPS data the data logger clock should be synchronized to GPS time
(UTC).
Sound Velocity Settings
The SonarMite default Speed of Sound in Water(SoS) setting is 1500m/second, facilities to vary
this have been provided in the calibration or in post processing. In practice this velocity value
can vary due to several factors …
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Water Temperature
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Water Salinity
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Water Turbidity
All of the above factors vary the density of the water in some way and effect the „time of flight‟
of a pulse of ultrasound in water and hence the depth calculated from this time by the SonarMite.
The user can either measure the speed of sound in water by taking velocity profiles using a
dedicated velocity measuring device or can use the SonarMite static over a known depth to a flat,
firm base and then compare the measured value with the known depth. The difference in Sound
Velocity between warm fresh water and cold salt water is about +/-30m/Second which represents
a change of depth of +/-2%, this must be viewed in context with typical depths of the survey, if a
typical depth is 10m then the error could be about 20cm.
The Sound Velocity setting is the
largest source of measurement error when care is not taken in setting it correctly.
Reverse Voltage Protection
The SonarMite DFX is protected from reverse connection or direct short circuit by an internal
diode and 1 Amp thermal fuse. If the fuse is tripped then the system will need to be disconnected
for 1 minute for the fuse to cool down and reset itself.
Weatherproofing
The SonarMite has been designed to conform to the IP65 waterproofing standard, this
benchmark describes equipment which can withstand a light spray of water from a hose for a
short period of time, it does not imply the device is suitable for immersion in any depth of water
or exposed to prolonged harsh weather conditions. The weatherproofing also assumes the
connectors or cover caps are fully screwed on to their rubber sealing rings. The weatherproofing
does not apply to certain components which are by definition not designed for outdoor use such
as the D9 serial or USB cable connectors.
