PHIND: an analytic model to predict target acquisition distance with image intensifiers.

An earlier developed calculation scheme to predict the visual range with image intensifiers is further elaborated and quantified. On the basis of the physical characteristics of the image intensifier and the observation conditions (target size and contrast and the meteorological visual range), the recognition distance for any value of the vertical illuminance can be calculated. The predictions were verified with a sizable experimental data set. The recognition distance for widely varying targets could be described on the basis of realistic physical target contrasts with respect to background and of a characteristic size which may be related to typical background clutter. PHIND FORTRAN and pocket calculator programs are available on request.