Page:Advanced Automation for Space Missions.djvu/29



about the state of the world and as a predictive mechanism for controlling observation satellites and interpreting observations.

The world model database must contain state component information about the expected character of points on the Earth. This includes land use (crop type, urban type, etc.) and ground topography. The world model theory component must predict some rather ubiquitous changes that occur, such as alterations in foliage color and foliage loss for certain vegetation areas as a function of season and precipitation history; ice formation and melting with the seasons; and variations in appearance of rivers from flow rate changes due to watershed runoff. As with the ensemble of observing satellites, it should be possible initially to set the Earth-sensing system into operation with a limited world-modeling capability, and later expand this model as the technology progresses. 103 pixels

AVERAGE 30 niches 15 CHARACTERISTICS 1 SENSOR VICTORIA, AUSTRALIA E141-45 10J 106 pixels VS. 450 CHARACTERISTICS 2,222 : 1 REDUCTION

Figure 2.8. - Sample niche features map of Mildura Gty, Victoria, Australia.

The key element in handling, processing, and storing data in the proposed satellite system is the use of a world model to abstract useful information from images and thus accomplish a large reduction in required data transmission and storage. The model gives the satellite "experience" by which to judge new observations. Data compression has been investigated in video imagery and, in some cases, compressions of 20:1 have been accomplished, but not at acceptable fidelity (Graham, 1967). It has been found that methods using feature extraction without benefit of a world model are capable of compression ratios in excess of 100:1 (Chien and Peterson, 1977). A world model permits still greater data compression by interpreting features and their established properties in the full context of the known land, sea, and atmospheric environment of the Earth.

The simplest world model is a flat land map. Figure 2.8 illustrates such a map of Mildura City in Victoria, Australia, representing an area encompassing 16 features in 5 distinct land types: (1) river, (2) lake, (3) forest, (4) cropland, and (5) city area. Each feature is termed a "niche" ? a surface feature on land or ocean possessing a relatively clear boundary, common features within that boundary, and whose location does not change rapidly with time. On land, niches are closely spaced, whereas in the oceans and atmosphere they may be quite large. Table 2.4 gives general characteristics of land, ocean, and atmospheric world models.