than the co 2 lines while water vapor emission in this region is five orders of magnitude weaker the blackbody emission from the 4 2 u03bcm region is weaker than that from the 15 u03bcm region for a temperature of 300 k the spectral distribution of blackbody radiation was calculated using planck 39 s function and is shown in fig3 for a 300 k temperature sample this figure shows that the blackbody radiation from the 13 u03bcm region is about one order of magnitude greater than the corresponding radiation from the 4 2 u03bcm region the variation of blackbody radiation with temperature was calculated for two wavelengths 4 2 u03bcm and 14 u03bcm the results are shown in fig4 and 5 the blackbody radiation at the 4 2 u03bcm band is about three times more sensitive to temperature changes than the 14 u03bcm band since the passive radiometric temperature sensing technique is based on the detection of small changes in atmospheric temperature the use of the 4 2 u03bcm band is more desirable in addition the 4 2 u03bcm band is not complicated by the presence of interfering gases the maximum range values of the individual spectral lines in the 4 2 u03bcm carbon dioxide band are shown in fig6 the lines which have the smaller absorption coefficients are associated with the longer ranges whereas the stronger emission absorption lines provide information at shorter ranges therefore.