Smear Camera Technique for Free-Surface Velocity Measurement

An optical technique which permits recording the position of a very small region of a surface as a function of time is described. The surface must reflect light specularly, the arrangement must allow some space in front of the surface, and the radius of curvature of the surface must be large compared with the distance over which the position is of interest. There are no other restrictions on the surfaces to which the technique may be applied. The apparent position of the image of an object reflected in the free surface to be studied is recorded with a moving-image smear camera, and velocity is obtained from the record of position as a function of time. This technique has been used to measure velocities between 5×103 and 5×105 cm/sec in times as short as 3×10−8 sec for research with high explosives.