Measurement of cloud solar reflected radiance and extinction from space lidar

Abstract

A method of obtaining the reflected solar radiance from clouds with space lidar is described. The lidar telescope and detector are used effectively together as a visible radiometer at the lidar wavelength, the background signal on a lidar backscatter profile being proportional to the observed radiance in the lidar field of view. A DC-coupled output from the telescope detector is required for this method. The RMS background noise signal is also proportional to the observed radiance, where a DC-coupled detector is still effective. However, an AC-coupled detector could also be used. Both the methods are used here to measure the relative radiance along a part of one orbit of the Lidar In-Space Technology Experiment (LITE) on Space Shuttle Discovery. This orbit crossed over Typhoon Melissa where the cloud was optically thick and the reflectance at 532 nm was estimated by normalization at maximum values to previously observed GMS satellite values over similar clouds. Retrieval of the radiance from the internal lidar parameters is also being investigated. Some profiles of extinction coefficient below cloud top near the center of Melissa were also retrieved, showing an increase in extinction below cloud top to at least a depth of 1 km.