Anomalies are identified if possible, catalogued, and appropriate action taken. Anomalies that cannot reliably be identified by IESIS are placed on file for transmission to a human analyst for interpretation and action. All sensor data are abstracted and summarized by feature and placed in the abstracted observation file for archiving and world model updating. Any user-requested processing is then performed and a user file established. These processes are shown schematically in figure 2.14.
2.4.2 Uplink and Downlink
The uplink sends detailed observational and processing schedules to IESIS satellites. A possible component of the uplink package is a set of sensor values expected to be observed during the next set of observations. This expectation is generated by using the world model as the standard against which to compare sensor observations so that anomalies may be identified. The uplink is illustrated in figure 2.15. Information needed during the next observation period is transmitted from the central processing facility via ground station and geosynchronous communications satellite up to the observation satellite as discussed in section 2.2.
NAVSTAR - GPS GEO-SATELLITE TDRSS LEO - EARTH OBSERVATION SATELLITE
IESIS
Figure 2.13,- IESIS satellite system.
LEO - EARTH OBSERVATION SATELLITE
The downlink reverses the uplink process by consolidating data gathered by satellite and returning them to the ground in one transmission. The downlink also uses the geosynchronous communications link to transmit data to a ground station which relays the information to the central processing facility. The process of downlink consolidation is illustrated in figure 2.16.
2.4.3 Image Processing
A primary IESIS requirement is the necessity to perform rapid and massive data reduction aboard the satellite in the sequence suggested in table 2.6. The focus is on image data acquired at high rates ? presently 120 Mb/sec for SIR, 85 Mb/sec for the Thematic Mapper, and in excess of 600 Mb/sec for SAR systems (Nagler and Sherry, 1978). Such rates may arise in each of perhaps 20 sensors in certain extreme cases of IESIS operations, which requires that the spacecraft carry onboard high-speed processors.
IESIS high-speed processors might evolve from faster serial logic devices, e.g., those which may be developed from Josephson tunnel technology. However, an alternative approach is the use of parallel logic to perform many operations simultaneously. By executing thousands of computations at once an intrinsic speed advantage equal to the number of individual processors is theoretically possible. In practice, this hypothetical limit may not be attainable due to pragmatic technological restrictions on each individual element in an array of thousands of processors. In spite of this, computing speeds within two orders of magnitude of the theoretical limit have already been obtained (Schaefer, 1980). Data handling using thousands of active elements simultaneously is called "parallel processing."
