International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part Bl. Istanbul 2004
conduct the range of functions currently performed by a few
large satellites today. There is a lead satellite in each group,
called group-lead; the other satellites are called member-
satellites. The group-lead is responsible for management of the
member-satellites and communication with other group-leaders
in the network (constellation), in addition to communication
with the geostationary satellites. This mode of operation is
similar to an intranet. The group-lead looks like a local server,
and the member-satellites look like the computer terminals.
The local server (group-lead) is responsible for internet
(external) communication in addition to management of the
intranet (local) network. This design can reduce the
communication load and ensure effectiveness of management
and coverage of data collection.
The second layer is composed of geostationary satellites
because not all EOSs are in view of or in communication with
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worldwide users. The second layer satellite network is
responsible for communication with end-users (e.g., data
downlink) and ground control stations, and ground data
processing centers, in addition to further processing of data
from group-lead satellites.
All of the satellites are networked together into an organic
measurement system with high-speed optical and radio
frequency links. | User requests are routed to specific
instruments maximizing the transfer of data to archive facilities
on the ground and on the satellite (Prescott er a/., 1999). Thus,
all group-leads must establish and maintain a high-speed data
cross-link with one another in addition to uplink with one or
more geostationary satellites, which in turn maintain high-speed
data cross-links and down-links with end users and ground
control stations and processing centers.
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Higher- Orbit Satellite
a 7 Real-time User
__ System Operation
Figure 1. The architecture of a future intelligent earth observing satellite (FIEOS) system.
2.2 Performance of Satellite Network
The normal operating procedure is for each EOS to
independently collect, analyze and interpret data using its own
sensors and on-board processors. These collected data will not
be transmitted to ground users, the ground station, or
geostationary satellites unless they detect changed data after the
data reprocessing is carried out onboard. If scientific users want
raw data, they can directly uplink their command for
downlinking the raw data. When an EOS detects an event, e.g.,
a forest fire, the sensing-satellite rotates its sensing system into
position and alters its coverage area via adjusting its system
parameters in order to bring the event into focus (Schoeberl ez
al, 2001). Meanwhile, the sensing-satellite informs member-
satellites in its group via cross-links, and the member-satellites
autonomously adjust the attitudes of their sensors to acquire the
event. The different sensors of a satellite group are located in
different height, different position and with different spectral
coverage, resulting in a multi-angle, -sensor, -resolution and -
spectral observation and analysis of the event. These data sets
are merged to a geostationary satellite that assigns priority
levels according to the changes detected. Following a
progressive data compression, the data is then available for
transmission to other geostationaries. The links between the
geostationary satellites provide the worldwide real-time
capability of the system. Meanwhile, the geostationary further
processes the data to develop other products, e.g., predictions of
fire extend after 5 days, weather influence on a fire, pollution
caused by a fire, etc. These value-added products are then also
transmitted to users.
If the geostationary cannot analyze and interpret the directly
collected data, the “raw” data will be transmitted to the ground
data processing center (GDPC). GDPC will interpret these data
according to user’s needs, and then upload the processed data
back to the geostationary satellites. In the satellite network, all
satellites can be independently controlled by either direct
command from a user on the ground, or autonomously by the
integrated satellite-network system itself.
The satellite transmits the image in an order of priority, where
the more important parts of the data transmitted first. For
example, the multi-spectral imagery of a forest fire may have
higher priority than the panchromatic imagery. Panchromatic
imagery for 3D mapping of a landslide may have priority over
the multispectral imagery. Of course, the autonomous
operation of the sensors, processors and prioritization
algorithms can be subject to override by system controllers or
authorized users.
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