How different are the cloud layer heights in GLA09 identified by the 532 nm and 1064 nm channels?
Users may note duplication of cloud layers in GLA09, meaning that a given layer is reported twice: once from 532 nm and once from 1064 nm (assuming that both channels are operating). If this occurs, the top and bottom of the layer should be slightly different, because two completely different algorithms are used to locate the layers. In general, the 532 nm and 1064 nm layer top for the same cloud layer will be within 150 m (2 bins) of each other. Most of the time, the 532 nm top height will be slightly higher than the 1064 nm top height. The cloud bottom height will at times be significantly different, especially for geometrically thick clouds. This is because the 1064 nm channel suffers from "signal droop," which causes loss of signal (above and beyond signal loss due to attenuation) as it penetrates down into a cloud. This effect will cause the 1064 nm cloud bottom to be significantly higher than that of 532 nm. Since the droop effect is very dependent on cloud optical and geometric depth, how much higher depends on the characteristics of the cloud itself.