By conducting an analysis of the measurement errors it was found that bubble dynamics obtained by two-point probes can be highly inaccurate. A fourpoint optical probe with appropriate data processing algorithm has been developed so that the bubble velocity vector can be obtained. This probe provides directly the value of specific gas-liquid interfacial area. However, for obtaining accurate values of bubble velocity and size, the four-point probe must be calibrated by a CCD camera at the same conditions. Calibration columns have been developed for this purpose where the bubble size and velocity can be varied to calibrate the measurements by the four-point optical probe against a CCD camera.