Overview

Summary

DARDAR CLOUD products (raDAR/liDAR cloud parameter retrievals)

This web-site describes the synergetic ice cloud retrieval products derived from the combination of the CloudSat radar, the CALIPSO lidar and MODIS measurements. The algorithm used to retrieve ice cloud properties, within a variational framework, is referred to as Varcloud. It was developed at the University of Reading by Julien Delanoë and Robin Hogan, Delanoë and Hogan (2008, 2010). Ice cloud retrievals are available at CloudSat horizontal resolution (1.4km) and CALIPSO vertical resolution (60m). This algorithm uses a variational method for retrieving profiles of visible extinction coefficient, ice water content and effective radius in ice clouds using the combination of radar reflectivity, lidar attenuated backscatter and infrared radiances in the atmospheric water-vapour window. The forward model includes effects such as non-Rayleigh scattering by the radar and molecular and multiple scattering by the lidar. By rigorous treatment of errors, and a careful choice of state variables and associated a priori estimates, a seamless retrieval is possible between regions of the cloud detected by both radar and lidar, and regions detected by just one of these two instruments. Thus, when the lidar signal is unavailable (such as due to strong attenuation), the retrieval tends towards an empirical relationship using radar reflectivity factor and temperature, and when the radar signal is unavailable (such as in optically thin cirrus), accurate retrievals are still possible from the combination of lidar and radiometer.

The algorithm can generate two products:

  • DARDAR-cloud : Ice cloud properties derived from CloudSat and CALIPSO (CALIOP) only.
  • DARDAR-rad-cloud : Ice cloud properties derived from CloudSat and CALIPSO (CALIOP) and IR radiances from IIR or MODIS. This product is not routinely available yet.

Version History

  • v2.1.0 : The latest release. Changes are :
    • - CALIOP v3.xx datasets used as inputs,
    • - clutter contaminated pixels removed before processing,
    • - better file attribute description.
  • v2.0.0 : First release of the products.
    • - CALIOP v2.xx datasets used as inputs (from June 2006 to February 2009 )
    • - WARNING : in this version, IWC can be artificially too large. We recommend that the user gets rid of any profile where IWC > 1 kg m-3.

Please do not hesitate to contact Julien Delanoë for any questions.

Publications

  • Delanoë, J., and R. J. Hogan, 2008: A variational scheme for retrieving ice cloud properties from combined radar, lidar, and infrared radiometer, J. Geophys. Res., 113, D07204, doi:10.1029/2007JD009000.
  • Delanoë, J., and R. J. Hogan, 2010: Combined CloudSat-CALIPSO-MODIS retrievals of the properties of ice clouds. J. Geophys. Res., 115, D00H29, doi:10.1029/2009JD012346.