1. A computer-readable medium containing software that, when read by a computer, causes the computer to perform a method for wide-area site-based surveillance, the method comprising: receiving surveillance data, including view targets, from a plurality of sensors at a site; synchronizing said surveillance data to a single time source; maintaining a site model of the site, wherein said site model comprises a site map, a human size map, and a sensor network model; analyzing said synchronized data using said site model to determine if said view targets represent a same physical object in the site; creating a map target corresponding to a physical object in the site, wherein said map target includes at least one view target; receiving a user-defined global event of interest, wherein said user-defined global event of interest is based on said site map and based on a set of rules; detecting said user-defined global event of interest in real time based on a behavior of said map target; and responding to said detected event of interest according to a user-defined response to said user-defined global event of interest, wherein said analyzing further comprises: updating existing view targets with new size, location and appearance information; determining if a new view target corresponds to an existing map target by comparing location information; and comparing appearances, wherein each view target includes an appearance model that includes a distributed intensity histogram, and wherein comparing appearances comprises: determining an average correlation between said distributed intensity histograms for each of said view targets and said map targets; merging said new view target into said existing map target, if said new view target corresponds to said existing map target, and updating said existing map target with said new view target; producing a new map target corresponding to said new view target, if said new view target does not correspond to said existing map target; and determining if two map targets correspond to the same physical object.