Derivation of convenient analytical expressions for the effects of atmospheric scattering and absorption on the performance of optical sensors, including the human eye, photoelectric detection systems, passive infrared scanners, and gated-viewers. The factor that limits the performance of each sensor is found in terms of the apparent radiance of the target and its surrounding background. The transmittance for this limiting factor can then be determined. Findings indicate that with commonly encountered visibility ranges and scene albedos, the performance degradation caused by the atmosphere differs widely between the various sensors. Passive infrared and gated-viewing systems, being unaffected by path luminance, are considerably less degraded in performance by a scattering atmosphere than are visual or photographic systems, while the degradation suffered by photon-noise-limited systems lies between these extremes.