Threshold detection in pulsed laser ranging

Suzaki and Tachibana (1972, 1973) have developed a method for detecting the arrival time of the return pulse in pulsed laser ranging based on the identification of the time at which the preset threshold level is exceeded by the output of the optical detector. The received optical pulse is considered to be made up of cells of width equal to the resolution time of the receiver and an equation is derived for P sub j, the probability that the threshold is first exceeded in the j-th cell. Using the density P sub j, expressions are obtained for the mean position of the cell at which threshold occurs and for the standard deviation (rms error) in the detection cell. The present paper maintains that, since the number j is purely an artifice for identifying the cells, its mean and standard deviation are inadequate for characterizing the detection cell and detection errors. It is proposed that if the detection cell is defined as the cell at which P sub j attains a maximum, then the above-cited ambiguity would be eliminated.