| 1 | High-resolution angle-Doppler imaging by sparse recovery of underwater acoustic signals显示文摘The low resolution of Fourier two-dimensional spatial temporal spectrum estimation and the insufficient sample size of sonar space time sampling data often caused difficulties in high-resolution space time spectrum estimation. Aiming to solve this problem, we proposed a high-resolution angle-Doppler imaging method and designed an anti-reverberation space time filter based on the sparse recovery of underwater acoustic signals. The proposed imaging method established the spatial temporal sparse representation model of array signal under the condition of few observation samples of single measurement vector(SMV), and reconstructed the high-resolution angle-Doppler profile of echo and reverberation through the matching pursuit(MP) algorithm and basis pursuit(BP) algorithm. By utilizing the space time distribution characteristics of echo and reverberation and the prior information of sonar rangecell under test(RUT), a reverberation dictionary composed of special space time guidance vectors was designed, and was used to reconstruct the reverberation and formed an anti-reverberation space time filter to suppress the reverberation interference of angle-Doppler plane. Computer simulations indicated that, under two conditions of forward and side-view array of moving sonar, the single measurement vector of sonar array was successfully used in the reverberation background to reconstruct the high-resolution angle-Doppler profile of low-speed moving target multi-spot echo. Its frequency resolution had a better performance than the Fourier resolution and the angle resolution broke through the Rayleigh limit of the array, the resolution was obviously superior to the Fourier space time spectrum estimation. | KOU Siwei FENG Xi’an BI Yang HUANG Hui | 2020 | Chinese Journal of Acoustics2020，39，2： | 1 |
| 2 | Mowing did not mitigate the negative effects of nitrogen deposition on soil nematode community in a temperate steppe显示文摘Soil nematodes are the most numerous components of the soil fauna in terrestrial ecosystems.The occurrence and abundance of nematode trophic groups determine the structure and function of soil food webs.However,little is known about how nitrogen deposition and land-use practice(e.g.mowing)affect soil nematode communities.We investigated the main and interactive effects of nitrogen addition and mowing on soil nematode diversity and biomass carbon in nematode trophic groups in a temperate steppe in northern China.Nitrogen addition and mowing significantly decreased the abundance of soil nematodes and trophic diversity but had no effects on nematode richness and the Shannon-Wiener diversity.Nitrogen addition influenced soil nematode communities through decreasing soil pH.Mowing influenced soil nematode communities through decreasing soil moisture.Nitrogen addition enhanced the bacterial energy channel but mowing promoted fungal energy channel in the soil micro-food web.Our study emphasizes that ecosystem function supported by soil organisms can be greatly influenced by nitrogen deposition,and mowing cannot mitigate the negative effects of nitrogen deposition on soil food webs. | YINGBIN LI SIWEI LIANG XIAOFANG DU Xinchang Kou Xiaotao Lv Qi Li | 2021 | Soil Ecology Letters2021，3，2： | 0 |
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