A Readout Technique for the Laser Fog Disdrometer

Abstract Recently a new instrument termed the laser fog disdrometer was introduced by Silverman, Thompson and Ward. As implied by the name, the function of the instrument is the determination of the size distribution of fog droplets. In design, operation and analysis this instrument represents a significant departure from the customary approaches to the problem. The basic principle of the instrument may be summarized as follows: by suitably storing the diffraction pattern associated with a droplet, both the precise size and location of the droplet may be determined. This principle can be utilized to obtain size distributions without disturbing the statistics of the sample, i.e., finite volumes may be sampled without dilution. Originally, the data were read directly from the diffraction pattern. This type of readout is subject to two fundamental difficulties: 1) the geometry of droplets is difficult to ascertain except for simple structures; 2) if several droplets are relatively near each other in the samp...