System for, and methods of, providing for a determination of the

Abstract

Light from a moving airborne vehicle and scattered from atmospheric particles produces at first and second detectors at the vehicle, signals which are spatially and spectrally filtered, and conditioned by amplification and special filtering and converted to digital signals. The digital signals are edited and accepted if they satisfy certain conditions pertaining to a threshold variable with the average amplitude level of the noise plus signals. The digital signals from each particle are grouped. A centroid, based upon a weighting of the signals in each group with amplitude and time, is determined to represent the most probable time at which the particle crossed the peak of the illuminated region. The peak amplitude of each signal from the first detector is paired with the peak amplitude of the successive signals from the second detector. The time difference between the paired signals, and their product amplitudes, are determined. The amplitude products are separated into successive bins on the basis of the time difference between the signals in each pair and are averaged. The bin with the greated average amplitude product and the two (2) adjacent bins are selected. The median time in the bin having the highest average product amplitude is used as a first approximation to the transmit time of a particle. An estimate with enhanced accuracy may be obtained by calculating the 'centroid', by a method analogous to that used above, of a narrow distribution of events selected from those within the three (3) chosen bins.