In this research the sound file recorded for a moving airplane has been sliced into several frames using overlapped window. Then the array of each frame is transformed from the time domain into frequency domain using Fourier Transform (FT). To determine the characteristic frequency of the sound, a moving window technique was used, the size of that window is made proportional with the values of the tracked frequencies, the use of this adaptive window makes the difference with a previous research work conducted for the purpose, in that work a fixed-size window is used to track all characteristic frequencies. An algorithm was established to select the characteristic frequencies, this algorithm allocates the frequencies which satisfy the Doppler relation, beside that the tracked frequencies was chosen to be the most occurred frequencies in the power spectrum. Several sizes of the overlap windows have been tested to study the effect of window size on the accuracy of the determined radial velocity of the moving airplane. The obtained results have been compared with the corresponding results of non overlapped window. The accuracy of the results was assessed using two criterion, the first is the closeness of the curves of the determined radial velocities versus time for the case of overlapped and non-overlapped window; the closer curves indicate better results. The second used criteria is the Root Mean Square Error (RMSE), which is used to determine the linearity of the relationship between Doppler shift and characteristic frequencies, the least values of (RMSE) signify better results are obtained. Three values of the frame size have been tested; they are 0.1s, 0.15s and 0.2s. From the attained results it was found that the frame size 0.2s gives better results than the other tested sizes. In addition several values of window size have been tested; they are 0.01s, 0.03s and 0.05s, the best value is found 0.05s. Also the results indicated that the use of overlap window gives better results than the case of using non-overlap window.