A new method to retrieve cirrus cloud height with MODIS observations

We develop a new approach to inferring cirrus cloud top height (CTH) by using two nearby MODerate resolution Imaging Spectroradiometer (MODIS) shortwave infrared channels (i.e., 1.24- and 1.38-μm). The two channels are similar in terms of cloud scattering and absorption properties but are different in terms of water vapor absorption. With a combination of the two channels, the column water vapor amount above the cirrus clouds can be accurately extracted, and therefore the CTH can be retrieved. The new approach vanishes the impact of cloud optical and microphysical properties (i.e., cloud optical depth and effective size) on CTH retrieval. In comparison with the MODIS Collection 5 CTH product and the collocated Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) measurement, we find that the new approach retrieved CTH is much closer to the CALIOP CTH than MODIS is. The new approach can be applied to satellite-based instruments with the two channels, such as MODIS and the Visible Infrared Imager Radiometer Suite (VIIRS), and it can be considered as a complementary method for inferring thin cirrus clouds in the upper troposphere.