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 communication satellites to orbital IESIS components that acquire and process the desired data and return them to the ground processor through a downlink (section 2.4.2). The ground processing unit further refines the information obtained, if necessary, then delivers it to the requester (fig. 2.4).

IESIS nominally operates with only one human in the loop - the user. This high degree of autonomy enables the system to be cost-effective and capable of rapid response. The sequence of operations during any user/IESIS interaction is outlined in figure 2.5.

IESIS has two basic modes of operation called background and foreground. The background mode of operation performs continuous goal-oriented observations of Earth and abstracts from these useful information for storage in a readily accessible, cross-referenced database. Background mode builds a broad scientific knowledge base that provides useful historical data at low cost for theory verification and testing. The foreground mode allows individual users to request that observations be taken and processed in nonstandard ways. The system must be sufficiently intelligent to help "naive users" obtain the information they want in an optimal or near-optimal fashion without restricting or unduly burdening the more sophisticated user.

2.2.1 Background Mode

In background mode IESIS continuously observes the Earth and gathers information to update the world model and to identify anomalies (sensor readings differing significantly from the expected). The system uses its world model to eliminate transmission of duplicate data and to implement basic principles of management by exception. The IESIS world model describes the topography and environment of Earth and can predict what a member satellite should record during its next observation period. During that period, the system collects data for "features" (e.g., lakes, forests, coastlines) and identifies all anomalies. Feature information is summarized to specify feature status without describing every pixel observed. For instance, if the height of a lake is known at its inlet and outlet, then the lake height at all points and flow rate can be determined. Only two pieces of data need be stored and transmitted by IESIS, rather than complete data for each pixel of the lake.

Anomalies are of two types. The first consists of transient normal events occurring at random, which are not to be permanently included in the world model. Examples are ships on an ocean, cars on a road, an iceberg, or a forest fire. IESIS should be capable of identifying such events by

SENSORY DATA  ON BOARD PROCESSING  NATURAL LANGUAGE INTERFACE

DATA BASE      PROCESSING               WORLD   MODEL

Figure 2.4. - IESIS response to user request for information that requires satellite observation.