From the standpoint of remote sensing, the scattering and radiative transfer properties of model cirrus clouds with hexagonal columns and plates in visible, near-IR, and IR spectra have been investigated by using the improved ray-optics theory and adding/doubling method. The radiative properties for eight types of water clouds are also studied. It is shown that the single scattering and multiple scattering properties of clouds depend strongly on the cloud macro- and micro- physics, and wavelengths. The analysis of brightness temperatures (BT) indicate that measurements of BT at 2.16, 2.7, and 3.1 micrometers from space may be used to distinguish cirrus clouds from water clouds. Furthermore, a technique for detecting clear skies and cirrus clouds is developed by analyzing the BT difference in both IR windows, i.e., 11.2 and 13.34 micrometers .