Thales MobileMapper Beacon, User Manual

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• The low frequency has benefit in penetrating tree-cover,
but it is also susceptible to man-made sources of noise
from various electronics or electrically driven equip-
ment. This susceptibility shows up in reduced SNR,
which could lead to less reliable reception.
• ·Local Area Service - beacon is a local area service
where only one station is providing correction data to the
user-base. This is a strength such that it provides good
quality corrections when near the beacon site. Spatial
Decorrelation does enter the picture as you operate away
from the station. However, it's possible that Coast Guard
beacon DGPS could handle large ionospheric distur-
bances better than WAAS/EGNOS, although a rare con-
dition.
Benefits of WAAS/EGNOS
• High Frequency - WAAS / EGNOS transmit with a
pseudo-GPS signal at L1 frequency. This signal will be
available anywhere the GPS receiver's antenna can 'see'
the satellite. This provides a very wide operating area,
with the exception of behind certain large objects that
can mask the signal.
• Robust Reception - Being line of sight, and being trans-
mitted on L1 frequency, the WAAS/EGNOS signal is
typically easy to acquire. Interference with GPS is typi-
cally rare, which provides you with a robust service,
when the satellite(s) can be viewed.
• Wide Area Service - WAAS and EGNOS use a wide area
format for their service. A network of reference stations
compute corrections for the specific errors in the GPS
service (ionosphere, satellite orbit, and clock correc-
tions). It's possible that the reference stations in the net-
work are not of sufficient density, and they cannot pick
up subtle changes in the ionosphere.