Toward a Standard Procedure for Validation of Satellite-Derived Cloud Liquid Water Path: A Study with SEVIRI Data

Abstract Differences between satellite-derived and ground-based values of cloud liquid water path (LWPsat and LWPgr, respectively) in validation studies are partly associated with the validation itself, in particular with scale differences and parallax. This paper aims at establishing standards for validation procedures to minimize these contributions to the differences. To investigate this, LWP values were collected as computed from ground-based microwave radiometer (MWR) summer measurements made at two Cloudnet sites and from the spaceborne Spinning Enhanced Visible and Infrared Imager (SEVIRI) instrument. The large number of all-sky sample pairs (∼2500 after selection) formed an essential condition for the present study. The best validation method was determined by optimum statistical agreement between LWPsat and LWPgr. The method consists of (i) computation of LWPsat by averaging LWP over the pixels surrounding the ground station by means of a Gaussian weight function with a length scale defining the ...