Comparison of Three Methods in Extracting Coherent Modes from a Doppler Backscatter System

• Published in: Chinese physics letters Vol. 32; no. 12; pp. 92 - 95
• Main Author: 张小辉 刘阿娣 周楚 胡健强 王明远 俞昌旋 刘万东 李弘 兰涛 谢锦林
• Format: Journal Article
• Language: English
• Published: 01.12.2015
• Subjects: DBS; 后向散射; 多普勒频移; 导数法; 提取; 相位谱; 相干模式; 系统
• ISSN: 0256-307X; 1741-3540
• DOI: 10.1088/0256-307x/32/12/125201

We compare three different methods to extract coherent modes from Doppler backscattering （DBS）, which are center of gravity （COG） of the complex amplitude spectrum, spectrum of DBS phase derivative （phase derivative method）, and phase spectrum, respectively. These three methods are all feasible to extract coherent modes, for example, geodesic acoustic mode oscillation. However, there are stilI differences between dealing with high frequency modes （several hundred kHz） and low frequency modes, （several kHz） hiding in DBS signal. There is a significant amount of power at low frequencies in the phase spectrum, which can be removed by using the phase derivative method and COG. High frequency modes are clearer by using the COO and the phase derivative method than the phase spectrum. The spectrum of DBS amplitude does not show the coherent modes detected by using COG, phase derivative method and phase spectrum. When two Doppler shifted peaks exist, coherent modes and their harmonics appear in the spectrum of DBS amplitude, which are introduced by the DBS phase.