Page:Advanced Automation for Space Missions.djvu/344

 ils are commonly quite large. The ground model is necessary as a master for updating and against which the various satellite models may be calibrated. The ground model includes the library and archiving functions of the whole system. Land and ocean database technology requirements are: • Identification and characterization of important niches on land, ocean, atmosphere, and in boundary regions between • Optimum niche size for use in space image processing • Determination of well separated, easily identified niches to serve as geographical footprints • Compact representation of niche boundaries • Optimum sensor combinations for each niche • Optimum sensor combinations for boundaries • Anomaly specifications for niches • Convergent set of niche specific characteristics • Nominal values for niche characteristics in each niche in each sensor and for various sensor combinations such as sensor ratios • Dynamic models for temporal variations of land, ocean, and atmospheric niches • Optimum coordinate system for storing world model for computer readout in strips during orbital pass • Optimum distribution of a complex world model within a multi component system • Advanced data cataloguing • Models of the users and their requirements.

6.1.2. Earth Atmospheric Modeling The choice of sensor measurements most appropriate for terrestrial meteorological monitoring will require great advances in our present understanding of the atmosphere. Because of their dynamic and highly interactive character, the boundaries of homogeneous atmospheric three dimensional niches will be far more difficult to define than surface niches whose features are essentially stationary by comparison. An important stage in the development of the Intelligent Earth-Sensing Information System will thus be the definition of useful niche concepts. Choosing measurements important for monitoring the Earth's atmosphere will also require great advances in present understanding of both lower and upper atmospheric phenomena. Lower atmosphere. Examples of possible lower atmosphere niches might be regions where (a) certain temperature or pressure regimes such as low-pressure cyclones are operative, (b) there is a concentration of a particular molecular species, or (c) there is a characteristic cloud pattern indicative of an identifiable dynamic process. Such niches will often overlap, being highly interactive and transient. If the concept of a niche is to be efficient its boundaries should be essentially independent of its major properties, although property dependent niches could also be very use ful. Lower atmospheric niches are time-varying in size and location, constantly appearing, disappearing, and merging. The size of each niche will depend partly on the complexity of the atmospheric region and partly on requirements for effective monitoring or modeling. For example, atmospheric niches near the Earth's surface will undoubtedly be smaller than those in the upper atmosphere because of the complexity of surface weather patterns and of the need to have detailed niche descriptions to develop adequate meteorological models. Properties measured in lower atmospheric niches will include a wide range of parameters -pressure, temperature, humidity, cloud cover, wind speed, rainfall, atmospheric components, etc. Each property will have its measured values processed within the three-dimensional niche in a useful niche-dependent manner. This may be used to extract data showing, for example, the average rainfall in a niche area, its gradient toward niche boundaries, patchiness of the rainfall pattern, and higher-order characteristics. Since the atmospheric niche sizes are large, the savings from averaging three-dimensional data can be huge. To ensure that niche properties such as rainfall are faithfully reproduced over the niche, the number of higher-order characteristics such as Fourier components of the data may be large, perhaps several hundred. Another alteration of the land sensing concept must be made when comparing incoming observations to a resident world model on board the satellite. To meet Earth's needs, satellite descriptions of local weather should be continually updated together with models of the processes involved so that predictions may be made. The ephemeral and interrelated nature of many of the weather pattern-defining niches will make comparisons of current with previous observations difficult to interpret. The changing values and spatial extent of niches characterizing temperature, moisture, or pressure must be understood within the context of a complete model of weather activity. If local weather models are part of the resident world model, elaborate adaptive modeling must occur on board to correlate the incoming niche observations and to fit them into a model. In the case of lower atmospheric weather, it may be most efficient to transmit complete niche descriptions from every pass of the satellite for on-ground modeling to determine, say, the appearance of storms (high and low pressure areas) using complex pattern recognition algorithms, weather expert systems, and large computer storage. Niches which are large or do not involve complex interfacing or modeling in conjunction with other niches lend themselves more easily to comparison with world land models. Changes in large-scale gradients and global trends in temperature, particulates, andrain