北斗卫星导航系统是着眼于国家安全和经济社会发展需要,自主建设运行的全球卫星导航系统,是国家重要时空基础设施。随着北斗导航的应用场景不断深入,面对北斗导航弱干扰源的到达时间差(time difference of arrival, TDOA)定位方法出现...北斗卫星导航系统是着眼于国家安全和经济社会发展需要,自主建设运行的全球卫星导航系统,是国家重要时空基础设施。随着北斗导航的应用场景不断深入,面对北斗导航弱干扰源的到达时间差(time difference of arrival, TDOA)定位方法出现的时延估计难和定位误差大等问题,提出了一种自适应滤波广义互相关的时延估计方法,并结合Chan-Taylor解算定位干扰源。该方法首先通过自适应滤波对原始干扰源接收信号进行降噪处理,然后通过广义互相关(GCC)进行时延估计,解决在低信噪比情况下传统互相关时延难以估计的问题,然后通过Chan-Taylor的解算方法提升定位准确度。通过仿真验证该方法相比GCC-ChanTaylor在均方根误差(root mean square error, RMSE)有较好的提高,结果表明在低信噪比情况下该方法对北斗导航弱干扰源定位具有优越性。展开更多
The objective of this study was to investigate whether there was distinctive seasonal and zonal variation in the species diversity, biomass, and element accumulation capacities of macroalgae in two major intertidal ma...The objective of this study was to investigate whether there was distinctive seasonal and zonal variation in the species diversity, biomass, and element accumulation capacities of macroalgae in two major intertidal mangrove stand types （Avicennia marina assemblage andSonneratia apetala assemblage） in the Zhanjiang region of southern China. Over a year, 31 species in 15 genera were identified in both mangrove assem-blages, of which the dominant species wereCladophoropsis zollingeriand Enteromorpha clathrat.Macroal-gal species were significantly most abundant in spring （p〈0.05）, followed by summer, winter, and autumn. Variation in the zonal distribution of macroalgal species was conspicuous in both intertidal mangrove as-semblages, with the greatest abundance in the middle zone, and the least in the front zone. Patterns in the seasonal and zonal variation in macroalgal biomass in theS. apetalaassemblage were similar to those of macroalgal species diversity in both mangrove assemblages. The seasonal patterns in tissue concentrations of 15 analyzed elements were not uniform among the macroalgaeC. zollingeri,E. clathrata, andGracilaria salicornia in theA. marina assemblage. All three species exhibited variation in their responses to ambient concentrations of different elements, implying their differential ability to absorb and selectively accumulate certain elements.展开更多
文摘北斗卫星导航系统是着眼于国家安全和经济社会发展需要,自主建设运行的全球卫星导航系统,是国家重要时空基础设施。随着北斗导航的应用场景不断深入,面对北斗导航弱干扰源的到达时间差(time difference of arrival, TDOA)定位方法出现的时延估计难和定位误差大等问题,提出了一种自适应滤波广义互相关的时延估计方法,并结合Chan-Taylor解算定位干扰源。该方法首先通过自适应滤波对原始干扰源接收信号进行降噪处理,然后通过广义互相关(GCC)进行时延估计,解决在低信噪比情况下传统互相关时延难以估计的问题,然后通过Chan-Taylor的解算方法提升定位准确度。通过仿真验证该方法相比GCC-ChanTaylor在均方根误差(root mean square error, RMSE)有较好的提高,结果表明在低信噪比情况下该方法对北斗导航弱干扰源定位具有优越性。
基金The Public Science and Technology Research Funds Projects of Ocean in China under contract Nos 201305021 and 201105008-E
文摘The objective of this study was to investigate whether there was distinctive seasonal and zonal variation in the species diversity, biomass, and element accumulation capacities of macroalgae in two major intertidal mangrove stand types （Avicennia marina assemblage andSonneratia apetala assemblage） in the Zhanjiang region of southern China. Over a year, 31 species in 15 genera were identified in both mangrove assem-blages, of which the dominant species wereCladophoropsis zollingeriand Enteromorpha clathrat.Macroal-gal species were significantly most abundant in spring （p〈0.05）, followed by summer, winter, and autumn. Variation in the zonal distribution of macroalgal species was conspicuous in both intertidal mangrove as-semblages, with the greatest abundance in the middle zone, and the least in the front zone. Patterns in the seasonal and zonal variation in macroalgal biomass in theS. apetalaassemblage were similar to those of macroalgal species diversity in both mangrove assemblages. The seasonal patterns in tissue concentrations of 15 analyzed elements were not uniform among the macroalgaeC. zollingeri,E. clathrata, andGracilaria salicornia in theA. marina assemblage. All three species exhibited variation in their responses to ambient concentrations of different elements, implying their differential ability to absorb and selectively accumulate certain elements.
