Sub-pixel Response (3 of 3)

Figure 4b shows the radiance temperature difference, between the 3.9 um and the 10.7 um wavelengths as a function of cloud fraction. In this case (ground at 300 K and cloud at 260 K) the radiance temperature difference reaches a maximum of nearly 6 K, at about 65% cloud cover. The difference in radiance temperature may be of value in determining sub-pixel information about the clouds. If uniform cloud and ground cover (whose temperatures are known) can be assumed, then the fractional amount of cloud can be determined (if the effects of diffraction, emissivity and atmospheric moisture can be ignored).