Symmetrical FFT for Migrating Waves

by Joe C. Willis, (M.ASCE), Research Hydr. Engr.; U.S. Dept. of Agriculture Sedimentation Lab., Sci. and Education Administration, Oxford, Miss. 38655,

Serial Information: Journal of the Environmental Engineering Division, 1982, Vol. 108, Issue 5, Pg. 963-967

Document Type: Journal Paper

Abstract: A Fast Fourier Transform (FFT) technique is developed to analyze migrating waves for phase relationships as well as spectra. The problem of phase leakage, which arises through the use of finite data records, is more severe than previous analyses have indicated. This severity prevents extraction of meaningful phase relationships by the usual application of asymmetrical, FFT algorithms. The symmetrical method combines the accuracy of the lengthy correlation transform method with the speed of the FFT and gives residual leakage corresponding to that of usual analyses. Adverse effects of the residual leakage can be virtually eliminated by applying a cosine taper to the data records.

Subject Headings: Leakage | Fourier analysis | Wave spectrum | Data analysis | Asymmetry | Algorithms | Correlation |

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