Can the DIRSIG model simulate the “adjacency effect”?
Yes, and no. The “adjacency effect” is the contribution of photons that are reflected into the atmosphere by an object of interest near the target, which are then subsequently scattered by the atmosphere toward the sensor. This component of the radiance reaching the sensor appears to have originated at the target, but it is “colored” by the nearby object and the atmosphere that scattered it rather than by the target. As of version 4, the MODTRAN model supports modeling adjacency using the DISORT multiple-scattering features and addition set of cards in the Card #4 set. To use this method, the user needs to provide the reflectance of the target and the average reflectance of the surround. Using this capability in MODTRAN, the DIRSIG model could incorporate adjacency photons if it called MODTRAN for each pixel. However, this is not computationally tractable since a single run of MODTRAN in this mode can take 10’s of minutes. When expanded to millions of pixels, a single DIRSIG simulation
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