Comparison of MODIS optical depths with CALIPSO.

One month of collocated MODIS and CALIPSO layer optical depths are compared using a newly implemented CALIPSO cloud optical depth retrieval for single layer, optically thin cirrus with the goal of evaluating the MODIS retrieved cloud optical properties. This CALIPSO retrieval algorithm can be applied to cases with an elevated cloud layer surrounded by clear air. The lidar attenuated molecular backscatter signal from above and below the layer is used to compute the layer transmittance, and hence optical depth. This methodology reduces the retrieval uncertainties by not requiring assumptions about the physical or optical properties of the cirrus. Using the retrieved optical depths, the MODIS cloud optical retrievals are evaluated. We also provide a verification of the CALIPSO layer transmittance measurement with collocated Cloud Physics Lidar (CPL) data, and data from ground based lidar instrumentation.