Campbell Scientific ST-21 Argos Satellite Transmitter - Manual (Page 13)

ST-21 Argos Satellite Transmitter
FIGURE 3-2. The 12022 antenna
3.2 Environmental Enclosure
The ST-21 is designed to work in a dry, non-condensing environment. A
proper enclosure should be used to keep water, dust and other environmental
contaminates away from the ST-21. Always use desiccant inside the enclosure
to keep trapped moisture from condensing on the electronics.
4. Satellite Orbit Patterns
At least two NOAA Polar Orbiting Environmental Satellites (POES) carry the
Argos transceivers and are operational at any given time. The orbits carry the
satellites over the North and South poles of the Earth in a sun synchronous
pattern. Orbit period is close to 102 minutes. The satellite foot print is about
5000 km in diameter. At latitudes greater than 75 degrees, each satellite
provides coverage each pass. Each satellite passes over the poles 14 times a
day providing 28 satellite passes per day. Coverage decreases with latitude.
At the equator the PTT will “see” a satellite six or seven times a day. The
duration of the POES satellite visibility depends on the angle from the PTT to
the satellite. If the satellite passes directly overhead, the satellite will be visible
for about 15 minutes. If the satellite passes close to the horizon, as viewed
from the PTT, the satellite will only be visible for a short time. On average,
each satellite pass is visible for about ten minutes. If using a 200 second
repetition rate, a satellite pass could result in three received messages from the
PTT.
Satellite coverage must be considered when planning data collection and
transmission. Given the variability of satellite coverage, hourly data cannot be
expected unless the PTT is located above 75 degrees latitude. The number of
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