Patent US 4,259,592

In a ceilometric system, light pulses are emitted from a transmitter towards overhead clouds and reflected back down towards a receiver which generates a photodetector signal transmitted by a gate whose gating interval is shifted in time relative to the light-pulse emission instant to define successive range steps. During each dwell at a particular gating interval and range step, the photodetector signal is integrated to develop an integral signal for that range step. The integral signal for each range step is digitalized and stored in a digital storage circuit, ordered in correspondence to the sequence of the range steps. A microprocessor searches for the largest one of the stored integral signals and derives a ceilometric indication in dependence thereon.