Modification of power spectrum density of wavefront after applying window

Big error would be introduced in numerical computation of power spectrum density(PSD) because of the use of the weighted window function. Using simulated single-frequency wavefront, PSD values before and after applying Hanning window were computed and a modification factor was deduced using theory of Fourier transform. Relationship between wavefront frequency and modification factor was analyzed by theoretical computation. It shows that under certain measurement errors and certain frequency scope, a constant, 8/3 or 64/9 is effective to modify one-dimensional or two-dimensional PSD value after applying Hanning window.