MODELING OF GLOBAL CHANGE PHENOMENA WITH GIS USING THE GLOBAL CHANGE DATA-BASE .2. PROTOTYPE SYNTHESIS OF THE AVHRR-BASED VEGETATION INDEX FROM TERRESTRIAL DATA

Part I of this article reviewed an approach to modeling in scientific geographic information systems (GIS) by digitally synthesizing environ mental parameters or phenomena as functions of other data. This intera ctive approach to global environmental modeling complements the approa ch of dynamic process models while enabling the scientist to rigorousl y assess the character of data used as boundary conditions in other mo dels on widely available personal computers and workstations. Part II presents a case history using existing GISs to recreate the AVHRR-base d vegetation index using data derived from in situ study on the Earth' s surface. The example explores the relationship between the global ve getation index and ecosystems, soils, and precipitation, and defects i n our present ability to describe these features. The degree of succes s of the model shows that GIS and the global change data base can be e ffective modeling tools, especially when functions are added to enhanc e the modeling capabilities of GIS. One function, INDEX, developed for this case history, is a simple utility that models a single data set as a function of another data set. A second function THEMCOIN, takes t wo input categorical data sets, such as vegetation and soils maps, and computes the mean and standard deviation of a third input data set Of numerical values, such as elevation, precipitation, or vegetation ind ex computed from AVHRR data. THEMCOIN outputs a table of these empiric al relationships. It also optionally models the numerical data set bas ed on correlations with the categorical data sets. Both of these funct ions facilitate environmental modeling in GIS. The models begin to app roximate vegetation index as a function of ecosystem, precipitation, a nd soils. Statistical output from the models extends our understanding of relationships between environmental parameters.