2695 Series Operation Manual
EZT-2695-8000/1
Page
7
of
124
1. Introduction to the 2695 Easytrak Nexus
This manual provides the user with information on the installation, operation and maintenance of
the Easytrak Nexus Lite Ultra-Short Base Line (USBL) underwater acoustic positioning system.
USBL systems are used to position underwater items including Side Scan Sonars
*
, ROVs
†
, AUVs
‡
,
and divers.
With no compass input, a position will be SHIP (bow) referenced, e.g. 123m ‘X’ means 123m from
the starboard side of the ship, whereas, with a compass, a position would be NORTH referenced;
123m ‘X’ means 123m from the ship East.
A position can either be ‘relative’ for example 123m ‘X’ and 234m ‘Y’ from the vessel, or ‘absolute’
for example 412789m East 5823456m North if a GPS receiver and compass is enabled.
A common complaint of many USBL systems is the long time and complexity in ‘getting going’.
Easytrak Nexus Lite has been designed so that it requires the minimum of user intervention; the
system can be ranging to beacons as soon as the transducer touches the water. Favourite system
and beacon setups can be saved. Visual elements can also be saved, for example day / night
colour schemes.
The display not only gives positioning data in text form, but also graphically. Beacons are
individually identified and colour-coded,
GREEN
– position OK,
ORANGE
– caution, prediction
being used, and
RED
– signal lost and cannot predict safely.
Because of multi-path reflections and other types of acoustic interference, the position can
occasionally be corrupted. In gating and smoothing modes, Easytrak has the facility to ‘gate-out’
wild values of velocity. The ‘out of gate’ positions are replaced by predicted values. Note the
compass must be enabled.
The Easytrak Nexus Lite transceiver is fitted with internal compass, pitch and roll sensors. The
pitch and roll sensors work to
±
80
°
, more than sufficient for boat work. The transceiver also
includes depth and temperature sensors.
Note:
Strong magnetic anomalies can be beyond the calibration range of the internal compass. It is
advisable, that a bearing check be performed prior to use.
Easytrak Nexus Lite is ideal for surveys. With a Global Positioning System (GPS) receiver
interfaced absolute positioning of divers, sonar fish, ROVs, or seabed objects in UTM (Universal
Transverse Mercator) co-ordinates can be achieved. With GPS, Easytrak Nexus can also be used
to navigate to and from the worksite indicated by an entered waypoint. Place marks can also be
added to log items of interest.
The necessity of determining an accurate velocity of sound (VOS) through water is critical. VOS
accuracy is important in two areas, (1) across the face of the transducer (used for measuring the
bearing and depression angle to a target), and (2), the distance to and from the target (the range).
To help overcome this source of error, a sound velocity profile may be loaded into Nexus.
Alternatively, if a sound velocity profile is not available, the operator can enter two values of VOS
*
Sonar system for seabed mapping
†
Remotely Operated Vehicle
‡
Autonomous Underwater Vehicle
Summary of Contents for Easytrak Nexus Lite 2683
Page 1: ...Easytrak Nexus Lite 2695 Series Operation Manual ...
Page 13: ...2695 Series Operation Manual EZT 2695 8000 1 Page 13 of 124 ...
Page 85: ...2695 Series Operation Manual EZT 2695 8000 1 Page 85 of 124 Summary Report ...
Page 86: ...2695 Series Operation Manual EZT 2695 8000 1 Page 86 of 124 Complete Listing of Dataset ...
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