  The two-sensor depth from defocus (DFD) technique for the measurement of drop
sizes in a spray is further developed to achieve higher spatial and temporal
resolution, to improve estimates of size and number concentration, and to
provide additional guidelines for the calibration and design of the optical
system for a specific application. The technique and these improvements are
demonstrated using the case of secondary atomization when a shock wave
interacts with a single drop. This is an application in which both high
spatially and temporally resolved number density and size distributions of
secondary droplets generated in the wake of the original drop are necessary.
