Abstract: After considering the effect of atmosphere, this paper derives an expression of radi-ance equation for any bady surface on earth received by a remote sensor, then discussesthe relation between the radiance and the emission spectrum (thermal infrared and microwave regions). The results indicate that if neglecting the effect of atmosphere, as body'stemprature T is with 300K or so, the radiance received by a remote sensor is propor-tional to T⁵ roughly for thermal infrared band (8~14μm), and the radiance isproportional to T for microwave band.