Transmitting waveform design and signal processing method optimization are effective ways to improve a sonar system’s detection performance. In this study, the spectrum and ambiguity function characteristics of pulse trains of frequency modulation (PTFM) signals were deduced and analyzed to address the problem of serious reverberation interference in the detection of low-speed targets in shallow water environments. The action mechanisms of PTFM signal parameters on the comb spectrum and bed of nails ambiguity function were identified. PTFM signal parameters were designed according to reverberation suppression requirements. The threshold was calculated using the estimate-before-detect method, and the comb spectrum waveform cognitive filtering detection algorithm is proposed. The simulation and lake experimental results show that the PTFM signals’ reverberation suppression ability for low-speed targets was better than it was for stationary or high-speed targets. The proposed method has good universality, which can improve the output signal-to-reverberation ratio (SRR) by more than 6 dB.

As an important grammatical resource, nominalization has drawn many scholars’ attention, in which the most representative one is Halliday’s research on nominalization, and the breakthrough of his study is chiefly reflected in the researches about scientific discourses. Inspired by Halliday, many researchers have carried out various empirical researches on nominalization in different discourses. This study reviewed four types of empirical studies on nominalization, which are nominalization in academic discourse, nominalization in non-academic discourse, comparison of nominalization in different discourses and translation of nominalization. Through reviewing these studies, limitations concerning research methodology, research materials and analysis procedures are discussed. Finally, the analysis suggests that researchers should take all types of nominalizations into consideration and further elaborate their functions in different discourses, moreover, researches should focus more on practical significance of the study in the future and try to offer learners more advice on the use of nominalization and construction of academic writing.

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