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General Issues > Telecommunications
Satellite Links
Some of today‘s real time networks use
satellite backup. There are plenty of satellite services waiting for subscribers.
Besides the well-established GEO satellite systems
INMARSAT and AMSC – SKYCELL, many new players have
shown up recently with LEO satellites: Orbcomm, Skybridge, Teledesic,
Globalstar, and Iridium. So far, some have had more success, others less.
Without going into detail, we would like to make
some general statements on how satellite services can be seen with respect
to real time emergency communications:
- geostationary satellite systems have proven reliability,
but the necessity of a properly-adjusted directional antenna might pose
a problem in a major eathquake
- in a densely-populated urban area, many of these
systems would require rooftop antennas, which could lead to costly and
fallable cabling
- providing global satellite services is an extremely
tough business—how many providers will be left after a decade of hard
competition? (We don´t want to swap 3000 transceivers.)
- the majority of satellite services tend towards
medium and high data rates (like Internet access), while seismic alert
messaging is typically a low-rate application
- there is a considerable delay in initiating communications
in a commercial multiuser satellite link due to negotiation (the subscriber´s
log-in procedure)
- if a seismic system is to include early warning
capabilities, there is a bottleneck in terms of the limited number of
sensors that can transmit data at one time
- the current pricing of global satellite services
is not encouraging for publically-financed projects
- the novel alternative of operating from a stratospheric
platform (a high-flying aircraft equipped with transceivers and loitering
for long periods above a city: skystation)
is not yet reality and must still demonstrate true 100% availability
For a seismic real time network, high flying based
on commercial satellite links is not as hopeful a solution as it might
appear at first glance.
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