Vector Sensor Reference Manual 134
and the satellite’s longitude will cause the satellite to appear lower on the horizon. If the EGNOS
signal becomes unavailable due to obstruction, COAST technology helps to maintain system
performance during times of differential outage.
When using SBAS correction data, the Vector Sensor is able to provide you with the azimuth and
elevation of the SBAS available satellites via a NMEA serial port command to aid in determining
their position with respect to the built-in antenna. More about this feature is described in Section
5.5.2.
WAAS and ESTB Coverage
Figure 1-3 depicts the current WAAS coverage as provided by the currently leased Inmarsat
Atlantic Ocean Region - West (AOR-W) and Pacific Ocean Region (POR) geostationary satellites.
This figure approximates signal coverage with white shading where each satellite is 5° elevation or
greater. Figure 1-3 also shows additional contours for 10°, 15°, and 20° elevations. Within the
white shaded coverage area, at least one of the two satellites is available by line of sight. Within the
overlap area, both satellites may be accessible. Although there is geographic coverage at higher
latitudes, practical usage of WAAS will be limited to environments where a relatively consistent
line of sight to either of the Inmarsat satellites from the Vector Sensor system.
Figure 1-4 presents approximate EGNOS System Test Bed coverage provided by the leased
Inmarsat Atlantic Ocean Region - East (AOR-E) and Indian Ocean Region (IOR) satellites. This
figure approximates signal coverage with white shading where each satellite is 5° elevation or
greater. Figure 1-3 also shows additional contours for 10°, 15°, and 20° elevations. Within the
white shaded coverage area, at least one of the two satellites is available by line of sight. Within the
overlap area, both satellites may be accessible. Virtually all of Europe, part of northern Africa, and
into the Middle East is covered with at least one signal. Most of Europe is covered by two signals.
Note - Currently, only the AORE-E satellite is broadcasting. Refer to Appendix D -
Resources for information on how to monitor the status of the ESTB.
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 Vector Sensor.
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