Improved Cloud Top Height Retrieval under Arbitrary Viewing and Illumination Conditions Using AVHRR Data

Abstract

Cloud top height is an important variable for both scientific and operational meteorological applications. Unfortunately, direct observations of cloud top height are generally not routinely made. This article develops a new hybrid method for estimating cloud top height from Advanced Very High Resolution Radiometer (AVHRR) data to help provide more abundant and accurate cloud top height estimates at low cost. It takes into account arbitrary viewing and illumination conditions which can affect the accuracy of both cloud shadow detection and cloud shadow-based cloud top height retrievals. Results were validated with data taken by NASA's ER-2 Cloud LIDAR System (CLS). The mean differences between the AVHRR-based cloud height estimates and the LIDAR observations for the two validation images analyzed are 0.45 km and 0.67 km. The sensitivity of the results to the parametrizations used by the new algorithm was also evaluated. Parameters can be chosen to minimize their effect on retrieved cloud top heights; the procedure executes quickly. Given the accuracy of the cloud top height retrievals, the method could be used routinely to provide cloud top heights for a wide variety of meteorological and hydrometeorological applications (e.g., numerical weather prediction, drought monitoring). With the improved spatial resolution (and reduced cost) of data from soon to be launched new satellite observing systems, proportionally higher accuracy and resolution for cloud top heights can be achieved economically using this method.