The visible and infrared imager carried aboard the DMSP satellites, which provides a variety of moderate (2. 7 km at nadir) and high-resolution (0. 6 km at nadir) imagery. During daytime passes, the OLS is normally configured to collect high-resolution visible imagery in conjunction with a single channel of moderate-resolution IR imagery. During nighttime passes the sensor configuration is usually reversed. Nighttime visible data are obtained with a high-performance photomultiplier tube that allows viewing in visible wavelengths of clouds and land areas illuminated by a quarter moon or brighter. City lights and the aurora can also be viewed quite clearly, with or without a moon.