A method is developed to study the synergism that can exist between horizon search radar and IR search and track (IRST) systems onboard ship under various meteorological conditions within the marine surface layer (<50 m). The method shows that four operational regions can be defined through the effect of the air-sea temperature difference and the air-sea water vapor pressure difference to produce sub- or superrefractive IR and rf propagation. It is also shown that no conditions can exist such that both IR and rf have subrefractive propagation. Applying the method to many meteorological observations shows that the method works quite well; however, it also indicates that there is not necessarily a detection range advantage to having both an optical and a radar system. However, the advantages to having an optical system are not solely dependent on its range performance. The precision with which an optical system can provide target track parameters, its ability to maintain track when radar systems cannot, and its ability to identify targets are synergisms that are quite significant.