This paper will focus on the effect of atmospheric conditions on EO sensor performance using computer models. We have shown the importance of accurately modeling atmospheric effects for predicting the performance of an EO sensor. A simple example has demonstrated how real conditions for several US sites will significantly change the Probability of Detection, and hence Recognition and Identification. The current state-of-the-art model for computing atmospheric transmission and radiance is, MODTRAN® 5, developed by the US Air Force Research Laboratory and Spectral Science, Inc. Research by the US Air Force, Navy and Army resulted in the public release of LOWTRAN 2 in the early 1970’s. Subsequent releases of LOWTRAN and MODTRAN® have continued until the present. The corresponding state-of-the art in sensor models, is the NVESD’s NVThermIP and soon to be released, NV-IPM. These models have also undergone an evolutionary process starting with the FLIR and ACQUIRE models to the present. NVThermIP, versions 2002 through 2009. NVTherm-IP has the capability to interface with 3rd party MODTRAN® software, along with a Beers law and table inputs. The replacement, NV-IPM, uses a different approach. It continues to use Beers law and table, however, its primary interface is via a library of pre-calculations. The capability to interface to a complete set of MODTRAN® inputs no longer exists. It is recommended that the full capabilities of MODTRAN® be used when modeling atmospheric transmission and radiance, and that this capability be added to the new NVESD NV-IPM.