SXBlue II GPS Series Technical Reference Manual
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Note - The satellite elevation angle lowers with increasing distance away from the
equator and from the satellite’s longitude. Although a good amount of signal
coverage is shown in Northern latitudes for both WAAS and EGNOS, it may not be
usable due to its low elevation angle and the potential for it to be obstructed.
Ideally, testing of the system in the area of its use is recommended to ensure that
the signal is sufficiently available.
Note - The SBAS signal coverage may be present in some areas without either
sufficient ionospheric map coverage or satellites with valid orbit and clock
correctors. In such a case, differential positioning with SBAS may not be
desirable or possible, as four or greater satellites (with correctors) must be
available to compute a DGPS position. The next section provides further
information on the ionospheric map features of SBAS and the SXBlue II GPS.
SBAS Ionospheric Map Extrapolation
To improve upon the ionospheric map provided by SBAS, the SXBlue II GPS receiver
extrapolates a larger ionospheric map from the broadcast coverage map, extending its
effective coverage. This allows the SXBlue II GPS to be used successfully in regions
where competitive products may not. For example, the extrapolation provides enhanced
coverage through the northern part of South America for WAAS, through the northern
part of Africa for EGNOS, etc.
Please note that the process of estimating ionospheric corrections beyond the SBAS
broadcast map would not be as good as having an extended SBAS map in the first
place. This difference may lead to minor accuracy degradation. As an example, Figures
C-5 depicts the broadcast WAAS and EGNOS ionospheric map extent and the
extrapolated version. As can be seen, the extrapolated grid extends further in all
directions than the broadcast one, enhancing usable coverage.
Figure C-5 Broadcast and Extrapolated Ionospheric Correction Map
