Application of multi-taper S-transform method in wind coherence estimation

Abstract

Accurate estimation of wind coherence based on field-measured is a fundamental issue in which sufficient frequency resolution at low-frequency range and low variance at high-frequency range should be satisfied together. With essential limitations, commonly-used Welch and multi-taper (MT) methods may not meet this requirement. A new multi-taper S-transform (MTST), which utilizes specially designed orthogonal time-frequency windows, has a great potential for wind coherence estimation. In this study, a comprehensive comparison of the applicability and accuracy of different coherence estimation methods is firstly presented. Based on simulated processes, the estimation coherences, including co-coherence and quad-coherence, are compared with different window widths and taper numbers in Welch and MT, respectively. Constrained by the parameter setting, existing commonly-used methods cannot achieve the trade-off between variance reduction and frequency resolution improvement. MTST has good performance for single-sample coherence estimation over the entire frequency domain. Subsequently, detailed model suitability evaluations of five wind co-coherence models are also performed. Three similar typhoons captured simultaneously at four heights are adopted. The statistical properties of decay parameters are presented, including the effect of separation distances, wind velocity, and different estimation algorithms. These assessment results are valuable for accurate and reasonable wind resistance design.