Simrad HS52, Instruction Manual

Page: 61 / 80

OPERATING INSTRUCTIONS
20222360 / E
53
Use of SBAS Corrections
It is possible either to specify which Geo satellite to track or to
let the receiver choose which Geo satellites to track using
Automatic mode. However, it is recommended specifying which
Geo satellites to track. This enables the receiver to keep better
track of the specified satellites without starting to search for
PRN numbers every time it looses track of the satellite.
In Automatic mode the receiver will select which two satellites
to track. Be aware that occasionally the chosen satellites might
be from two different SBAS systems.
The recommended setting is to select one or two Geo satellites
for tracking.
Height Aided GPS Position
In periods with weak satellite geometry, the position can be
made more accurate by using height aiding function in the
General submenu. Refer General , page 34.
The height aiding improves the solution by using the knowledge
that a vessel at sea has only small short-term variations in height
caused by heave. The long-term variations caused by tide are
taken care of in the system. The height value used, as input to
the GPS solution is a low-pass filtered value of the measured
height.
A start value for the low-pass filter should be specified for use at
system start-up. The value to use is the height of the Sensor unit
above the WGS-84 ellipsoid when the sea level is at its mean
value. This height can be found in the primary
Navigation/POS
display, where the HGT value is the GPS height. Refer
Navigation/POS Display , page 46. The value should be
monitored for some minutes, and the average value should be
used.
Note!
The height difference between mean sea level and the WGS-84
ellipsoid can be significant. Values b/- 100 meters can
be encountered.
For normal operation, height aiding should be set to
FILTER
(recommended) or OFF . When FILTER or FIXED is selected,
an initial height has to be entered.