Thank you Sean. I use the tileLoadProgressEvent in order to attach post processing stage as soon as “some” tiles have been loaded. This is enough to make czm_globeDepthTexture available.
However, the uniform becomes unavailable again (and Cesium throws an exception) as soon as the depth buffer is unused/empty (when nothing is in view while looking upward for example). I know this is a rare occurrence when using Cesium “normally” but it can be a problem for, say, a flight simulator 