Underwater target elastic acoustic scattering and other acoustic scattering components are aliasing together in the time and frequency domains, and the existing signal processing methods cannot recognize the elastic scattering features under the aliasing condition because of the resolution limitation. To address this problem, this study, which is based on the target echo highlight model, analyzes the characteristics of target acoustic scattering components when the transmitted signal is a linear frequency modulation pulse. The target acoustic scattering structure in the fractional Fourier transform (FRFT) domain is deduced theoretically. Then, filtering is used in the FRFT domain to separate the target elastic acoustic scattering components. In addition, noise suppression performance and filter resolution are discussed. The target rigid and elastic acoustic scattering components are separated. Experimental results show that filtering in the FRFT domain can separate the elastic scattering components from the target echoes. Moreover, separated elastic acoustic scattering components have consistent theoretical features, which lay the foundation for studying the elastic scattering characteristics further.

Underwater target detection based on fourth-order cumulant beamforming Xiukun Li, Hongjian Jia and Mei YangHarbin Engineering University, Harbin, Heilongjiang, 150001, CHINA; lixiukun@hrbeu.edu.cn; jiahongjian hrbeu@outlook.com; yhrbeu@163.com Due to the complicated influences of the sea environment, how to obtain target echo data with high SRR (Signal-to-Reverberation Ratio) (SNR: Signal-to-Noise Ratio) is the key issue for improving the capacity of underwater targets detection. Based on the array signal processing, this paper presents a robust and highresolution fourth-order cumulant beamforming method based on the characteristics of array aperture expansion of fourth order cumulant, and DOA (Direction of Arrival) estimation of target is achieved by forming a narrow spatial beam. For a wideband acoustic system, the fourth-order cumulant beamforming method is extended to the DOA estimation of wideband LFM signals, combined with fractional Fourier transform (FRFT). Reverberation and noise are filtered out in the FRFT domain to further improve the SRR and SNR of the target echo. Simulation and data processing results of active sonar target detection verify the effectiveness of the research methods.

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The aerial parts of Artemisia eriopoda (Compositae) afforded two new C (17)-polyacetylenes. Based on their IR, UV, EIMS, (1)H- and (13)C-NMR (DEPT) spectral data, the structures were elucidated to be (1,8 E,13 Z,16)-heptadecatetraene-4,6-diyne-3,11,12-triol and (1,8 E,12 E,14 Z)-heptadecatetraene-4,6-diyne-3,11-diol.

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