Understanding the movement of sediment in the nearshore region due to wave motion and longshore currents is important in beach erosion studies, and has tactical significance in beach front mine warfare. In the surf zone, an bubbles and sediment are both suspended within the water column. At the Naval Postgraduate School in Monterey, California, a sediment flux probe has been developed to study small scale processes. Using ultrasonic acoustic backscatter, the Coherent Acoustic Sediment Flux Probe (CASP) is capable of tracking the movement of scatterers within the surf zone. As it is important that the CASP system is capable of distinguishing between sediment and entrained air bubbles, laboratory experiments were run to determine the ultrasonic acoustic backscatter characteristics of surf zone bubbles. Bulk void fraction and optical sizing methods were explored to develop a means of measuring bubble populations produced in the laboratory for calibration of the backscattered energy received by the CASP system in the presence of bubbles.