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<br />". <br /> <br />constraints, and spatial and temporal scales of application. Coupled with these problems are the <br />problems of study area characterization and parameterization once the model is selected. <br />GuideIines for parameter estimation are normally few and the user commonly has to make <br />decisions based on an incomplete understanding of the model developer's intent. <br /> <br />To address the problems of model selection, application, and analysis, a set of modular <br />modeling tools, termed the Modular Modeling System (MMS) is being developed. The approach <br />being applied in developing MMS is to enable a user to selectively couple the most appropriate <br />process algorithms from applicable models to create an "optimal" model for the desired <br />application. Where existing algorithms are not appropriate, new algorithms can be developed and <br />easily added to the system. This modular approach to model development and application <br />provides a flexible method for identifying the most appropriate modeling approaches given a <br />specific set of user needs and constraints. <br /> <br />A major component of MMS is a geographic information system (GIS) interface to <br />facilitate model development, parameterization, application, and analysis. This interface permits <br />. application of a variety of GIS tools to lumped- and distributed-parameter modeling approaches, <br />These tools permit development and testing of a variety of objective characterization and <br />parameterization techniques. They also permit visualization of the spatial distribution of model <br />parameters and simulated state variables at a variety of temporal and spatial scales. <br /> <br />The linking of modeling and GIS tools provides a common framework in which to focus <br />multidisciplinary research and operational efforts to provide improved understanding of complex <br />water, energy, and biogeochemical processes. Current model development within MMS is <br />focused on hydrologic processes. The purpose of this paper is to provide (I) an overview of the <br />system, (2) an introduction to the concepts and capabilities ofMMS with a discussion of currently <br />available (1993) system components, and (3) a description of the GIS interface. <br /> <br />MMS OVERVIEW <br /> <br />The conceptual framework for MMS has three major components: pre-process, model, and post- <br />process (Fig. 1). The pre-process component includes the tools used to input, analyze, and prepare <br />spatial and time-series data for use in model applications. The model component includes the <br />tools to devc::lop and apply models. The post-process component provides a number of tools to <br />display and analyze model resultS, and to pass results to management models or other types of <br />software. The model component is currently the most fully developed of the three components. <br />However, a number of the pre-processing and post-processing tools are being developed, tested, <br />and made available for linkage to the model component. <br /> <br />A system supeIVisor, in the form of an X-window graphical user interface (GUI), is <br />proposed to provide user access to all the components and features of MMS. The present <br />framework has been developed for UNIX-based workstations and uses X-windows and Motif for <br />the aUI. The aUl provides an interactive environment for users to access model-component <br />features, apply selected options, and ~phically display simulation and analysis results. The <br />current GUI is being expanded and enhanced iilio the full system supeIVisor, incorporating tlJe <br />., . " . . <br />linkages needed to a~cess features'iri all the system components. . .' , , <br />. .. . , . . -' ~ ~ , '-' -...., <br /> <br />"; .. <br /> <br />[. .... ~.". . <br /> <br />'. jJ <br /> <br />2 <br />