SuperDARN meteor wind measurements in the mesopause region using the standard analysis of ACFs constructed from the multi-pulse sequence have several shortcomings. To overcome them, we have developed a new method to enable raw time series analysis without degrading normal SuperDARN ACF observations. The unevenly sampled raw time series is processed to detect only underdense meteor echoes to deduce line-of-sight neutral wind velocities and decay time constants. We installed this new code at the SENSU Syowa radar in Antarctica. Distributions of underdense meteor echoes show clear and expected dependency on distance from the radar, local time, and diffusion coefficient. By using diffusion coefficients as height information, we successfully obtained the structure of a downward phase propagating semi-diurnal tide, which has not previously been achieved by analysing normal SuperDARN ACF data.