Collocated measurements of boundary layer cloud microphysical and radiative properties: A feasibility study

First data from collocated, helicopter-based measurements of boundary layer cloud microphysical properties (effective droplet radius R \u3c inf\u3e eff , droplet number concentration N) and spectral radiative quantities (cloud optical thickness τ, cloud top albedo ρ, reflectivity ℛ) are presented. The in situ measurements of the microphysical cloud properties were collected by the Airborne Cloud Turbulence Observation System (ACTOS) attached to a helicopter by a 145 m long rope. Cloud spectral reflectivity was derived from radiances measured by grating spectrometers combined with downward looking optical inlets installed underneath the helicopter. Correlations between cloud microphysics and reflected radiation are presented for two cloud cases with different optical and geometrical thicknesses. On the basis of common retrieval techniques, τ and R \u3c inf\u3e eff are derived using a radiative transfer model. The results of the retrieval are compared to the collocated in situ measurements and data from the Moderate-Resolution Imaging Spectroradiometer (MODIS). Within the limitations of the relatively small data set, the feasibility of closely collocated microphysics and radiation data and their benefits were demonstrated. Copyright 2010 by the American Geophysical Union