Disclosed is an apparatus for monitoring hot waste water discharged from a power plant by using an airborne multispectral scanner system. The apparatus includes a first detector including a first image data collecting unit to obtain first image data and a liquid-phase nitrogen storing tank used to cool an image obtaining sensor, a second detector including a second image data collecting unit to obtain second image data, and a liquid-phase nitrogen storing tank used to cool an image obtaining sensor, a controller to process the first and second image data obtained by the first detector and the second detector, respectively, and an auxiliary liquid-phase nitrogen tank separated from the liquid-phase nitrogen storing tank. The auxiliary liquid-phase nitrogen tank complements liquid-phase nitrogen for cooling.