illumination, and the media through which it is viewed. The ratio of the radiances wave at two different length scan be use dwaterandvegetation to separate from clouds, snow, and b are lands (Schappell and Tietz,1977; ThorleyandRobinove,1979).(Theradianceratio for clouds, snow, landisessentially so these and bare the same, features must be separated on the bas is of absolute radiance.)two sensor canby These procedures be improved using data from several sensor simultaneously andsin a multidimensionalsensorspace.canprocess Machinessuch complicated algorithms and "see" clusters in higher dimensions. The higher the multidimensional volume, the more accurate the discrimination between closely related sensorial characteristics. The intelligent use of a world model requires autonomous, real-time identification of niches (through their features) and determination of characteristics. Real-time pattern recognition and signature analysis also must be accomplished to supply useful information to the user. Algorithms should be developed for identification, pattern recognition, and signature analysis. Statistical procedures arise naturally in various classification schemes because of the randomness of data generation in various pattern classes. Statistical theory can be used to derive a classification rule which is optimal because it yields the lowest probability of classification error, on average. Various studies have developed decision functions from sets of finite sample patterns of classes. These decision functions partition the measurement space into regions containing clusters of the sample pattern points belonging to one clan. Some clustering transformations have been used in the development of such functions. Once a function has been selected, the main problem is the determination or estimation of its coefficients. For efficient coefficient estimation, time-dependent training samples are needed. A wide variety of additional algorithmic techniques are needed. For example, texture analysis can be accomplished using gray-tone statistics and the time rate of change of spatial contrast along scan lines to distinguish among wheat, rye, and oats (Haralick et al., 1974; Mitchell et al., 1977). Below is a summary of technology requirements: • Rapid methods for area centroid and orientation determination • Rapid partitioning of image features • Motion and relative motion detection • Development of wide range of classification algorithms for user-defined applications • Multispectral signature ratioing analysis and multisensor correlations • Rapid texture analysis • Investigation of usefulness of focal plain transformations for satellite use • Schemes to allow disparate algorithmic techniques to interact to speed recognition process • Determination of parameters of decision functions for various classification schemes
6.1.9 Active Scanning The sensors discussed to date have been essentially pas sive -they do not generate the radiation they detect. For a variety of purposes, some satellite systems will engage in active scanning by highly efficient RADAR or LIDAR, all weather imagery, night-time imagery, absolute and differential height determination, absolute and differential velocity determination, atmospheric probing, and leading edge scanning. Of course the mission to Titan, relatively far from the Sun, will not have large amounts of power avail able for this purpose. Additional technology requirements include a fast, efficient computer for generating imagery from SAR, the ability to determine height differentials to within several centimeters at boundaries, and the ability to determine differential velocities to within about 1 km/hr at boundaries.
6.1.10 Global Management of Complex Information Systems Each mission explored by the study group consists of a very large, complex array of equipment and people widely geographically distributed, all of whom must work in a cooperative and coordinated fashion to achieve mission objectives. An important concern thus becomes the overall architecture of such a system, the way decisions are made and communicated, the coordination of tasks within the system, and tile flow of information. These types of difficulties are not new in human endeavors and have been addressed within several disciplines which focus on specific aspects of the problem. A brief review of relevant fields resulted in several recommendations for high priority research in systems theory and control, summarized below. Classical control theory. Systems which evolve according to well behaved physical laws describable in the form of differential equations have long been the domain of classical control theorists. The aerospace industry has been a prime user of this technology in the guidance and control of missiles and in the development of automatic pilots for aircraft. The system is usually modeled as shown in figure 6.1 which envisions an idealization of a physical system subject to stochastic disturbances (typically Gaussian). The system is observed and digressions from the preferred trajectory are noted. A controller working with the idealized model (expressed in the form of differential equations) and a specific objective (such as "hit a target within a given
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