Raim; Underwater Navigation; Dvl (Doppler Velocity Log) Peripheral; Usbl (Ultra-Short Baseline) Peripheral - Advanced Navigation Spatial OEM Reference Manual

distance travelled will be reset. The distance travelled can be checked in the odometer
configuration dialog to ensure that it has passed 1000m.
5. Once 1000 metres has been driven, press the read button and check that the automatic
pulse length check box becomes un-ticked and the pulse length value is read.
7.11

RAIM

RAIM stands for receiver autonomous integrity monitoring. It allows a GNSS receiver to detect and
exclude both faulty and fraudulent satellite signals. Spatial's internal GNSS is equipped with RAIM
and it is enabled by default.
7.12

Underwater Navigation

Spatial is able to provide accurate absolute navigation underwater when combined with
appropriate peripherals. There are several options for underwater navigation detailed below.
7.12.1

DVL (Doppler Velocity Log) Peripheral

DVLs provide 3D velocity underwater and allow Spatial to provide positional accuracy of
approximately 0.3% of distance travelled.
A DVL works by tracking velocity relative to the sea floor. They typically have a range of
approximately 100m. When the sea floor is beyond this range, the DVL provides velocity relative to
the water layer, however this is unable to account for water currents which can cause positional
accuracy to degrade faster.
When operating with a DVL, Spatial must have a starting position to navigate from. This can be
achieved by either allowing Spatial to get a GNSS fix while the underwater vehicle is on the
surface, or by manually entering the starting co-ordinates using the External Position Packet. The
typical setup for obtaining a GNSS fix is a waterproof glass dome housing the GNSS antenna,
mounted on the top of the vehicle.
Spatial contains built in support for DVLs from Teledyne and Linkquest and these systems can be
directly connected to Spatial using the GPIO pins. Advanced Navigation recommends Teledyne
DVL systems.
7.12.2

USBL (Ultra-short Baseline) Peripheral

USBLs provide relative 3D positioning underwater and allow Spatial to provide positional accuracy
of approximately 4m.
A USBL setup consists of a surface transponder, an underwater responder and two Spatial units.
The surface transponder is typically mounted on a ship and is connected to a Spatial unit. Another
Spatial unit is mounted on the underwater vehicle along with the responder. The surface Spatial
unit communicates with the underwater Spatial unit over a serial connection through a tether.
Please see Illustration 27. USBL systems typically have a maximum range from transponder to
responder of approximately 500 metres.
Spatial contains built in support for USBLs from Tritech and these systems can be directly
connected to Spatial using the GPIO pins.
Spatial OEM Reference Manual
Page 39 of 88
Version 2.7