The working band and its selection method of the U.S defense support program (DSP) are explored. A new method used to choose the optimal detection bands based on the background clutter model is proposed. The simplified parametric expression for scene radiation is deduced

and then the spatial clutter model is built. The synthetic signal-to-noise (SSNR) is given in analytic form. Finally

the optimal bands are chosen by searching all the scene clutter level space

target radiation characteristics space and the spectrum space

which provide the best system performance to detect some certain class of targets with the similar radiation characteristics under different clutter levels. The validity of the method is illustrated by examples. Calculation and analysis results indicate that the optimal detection bands are dependent on the scene clutter level and the target radiation characteristics. With two target radiation profiles

the optimal bands for DSP are 2.73~2.85μm and 4.2~4.43μm.