The application of phase arrays is growing for NDT applications. State of the art ultrasonic arrays consist of many small piezo-electric elements that can be excited separately to synthesize a desired wave front. This may vary from simple plane waves to complex-shaped focusing wave fields. An implicit requirement is that the source strength (sensitivity) of all elements is equal, to prevent artifacts in the generated wave front. The same holds for the detection of ultrasonic waves. In typical commercial ultrasonic arrays, however, the sensitivity variations can be significant: amplitude variations of ± 3 dB are not uncommon. Pulse-echo data can be used for calibration of element strengths, but has some limitations. Pulse-echo corrections can only be implemented accurately when the sensitivity in transmission is equal to the sensitivity in detection. For ultrasonic measurements this is not necessarily true when separate transmit and receiver arrays are used, but is also not evident when the same array is used. A new data-drive method is demonstrated that can be used to determine the frequency dependent sensitivity of each element in a phase array in emission and detection separately.