Estimation of Cloud Physical Parameters from Airborne Solar Spectral Reflectance Measurements for Stratocumulus Clouds

Abstract

A new method is proposed to retrieve various cloud physical parameters of water clouds from the solar-flux reflectances at four wavelengths measured by using the airborne Multi-channel Cloud Pyranometer (MCP) system. The MCP system was designed to measure the spectral reflectances at nine wavelengths in the visible and near-infrared region. The estimation procedure assumes a locally plane-parallel and vertically homogeneous water-cloud layer with monomodal particle size distributions of a fixed width. The cloud optical thickness τ500 and the effective particle radius re, of the water-cloud layer can be simultaneously retrieved from the MCP reflectances measured at the visible channel of ?=500 nm and at the near-infrared channel of ?=1650 nm. Under the assumption that cloud pressure height is known, the cloud liquid water content (LWC) can then be retrieved from the MCP reflectance at the oxygen absorption-band channel cantered at ?=760 nm. Finally, the in-cloud water vapor amount uH2O can be estimated from the MCP reflectance at the water vapor absorption-band channel centered at ?=938 nm. Using these directly retrieved parameters, we can estimate byproduct parameters such as integrated liquid water path, cloud particle concentration, and geometrical thickness of the homogeneous cloud layer. A reliably applicable range of the present method was estimated to be 1≤ on the other hand, coalescence might be dominant in thick clouds in the mature stage with precipitation.