Optical Current Meter Use in Southern California

The optical current meter is a stroboscopic device with which an operator may visually follow and gage the velocity of particles moving on the water surface. From early prototypes the meter has evolved to a field usable instrument with a low power telescope, an oscillating mirror in the line of sight of the telescope, a variable-speed battery-powered motor, and a tachometer which indicates the rotational speed of the mirror. Surface velocities are computed knowing the distance to the water surface and the angular speed of the oscillating mirror. Surface velocities must be corrected by an appropriate coefficient to represent the mean velocity in the vertical. The optical current meter will find its principal use in measurements of discharge under conditions that preclude use of conventional stream-gaging equipment.