一种高Q值单频水声信号放大提取电路的设计          下载免费PDF全文

李明勇  魏爱娟  兰江 《数字海洋与水下攻防》2018,1(2):76-80

针对水声信号所处环境复杂、背景噪声源多的特点,提出了一种基于JFET的超低噪音放大电路,该电路选用两片低噪音的场效应管2SK170作为第一级放大器件,经过CR高通滤波连接到同相放大电路,整体电路增益可达70dB;为进一步提升接收信号信噪比,结合双T滤波器特点优化设计出一种高Q值选频电路;通过Multisim14仿真表明,设计的电路在1 Hz处的电压噪声密度仅为2.4 nV/Hz^0.5,滤波器Q值可达25.6,结合实际电路测试结果表明,设计的电路能够满足水声测量要求。  相似文献   

BDS卫星失效对区域定位精度的影响评估     

徐炜  徐梅  严超  王涛 《大地测量与地球动力学》2018,38(11):1133-1136

基于STK软件实现了2016-09 BDS系统星座结构的仿真，并选取可见卫星数、DOP值、系统可用性作为评估BDS卫星星座设计结构的指标，分析单颗与全部倾斜轨道卫星（IGSO）、地球静止轨道卫星（GEO）失效后对我国大陆地区BDS系统可用性的影响。结果表明，IGSO4卫星与GEO5卫星失效后对BDS在区域的定位性能影响较大，失效后的GDOP值分别为1.98、2.16。取BDS卫星正常运行时区域平均GDOP最大值(S=2.60)作为系统可用性阈值时，系统可用性分别降低了1.79%、32.63%；阈值取2S(5.20)、3S(7.80)、4S(10.40)、5S(13.00)时，系统可用性均可达100.00%。GEO整体失效后BDS系统在高精度定位中仍部分可用，而IGSO整体失效后BDS系统可用性受到大幅度限制。因此，增加在轨备份卫星时需重点考虑GEO5、IGSO4，并适当增加IGSO卫星的数目。  相似文献   

Diatom‐based reconstruction of summer sea‐surface salinity in the South China Sea over the last 15 000 years     

Hui Jiang  Mads F. Knudsen  Marit‐Solveig Seidenkrantz  Meixun Zhao  Longbin Sha  Lihua Ran 《Boreas: An International Journal of Quaternary Research》2014,43(1):208-219

We present a new reconstruction of summer sea‐surface salinity (SSS) over the past 15 000 years based on a diatom record from piston core 17940, located on the northern slope of the South China Sea (SCS). The reconstructed diatom‐based summer SSS values for the modern period are in accord with instrumental observations of summer SSS in the area. Here, the modern summer SSS is primarily controlled by river runoff, in particular from the Pearl River. The reconstruction presented in this study shows that the summer SSS varied between 33.3 and 34.2 psu over the past 15 000 years. The long‐term summer SSS trend closely followed the trend of the orbitally controlled solar insolation at 20°N, suggesting that orbital forcing was the dominant driver of changes in summer SSS in this area. Comparisons to speleothem δ¹⁸O data and studies of surface hydrography in the region suggest that changes in solar insolation affected the summer SSS through changes in the East Asian Monsoon and sea‐level changes associated with the last deglaciation. Univariate spectral analyses indicate that centennial‐scale oscillatory variations in summer SSS were superimposed on the long‐term trend. During the deglacial period (c. 12 000–9000 cal. a BP), the dominant periodicity was centred around 230–250 years, whereas a ～350‐year oscillation dominated in the period 2200–4500 cal. a BP. The balance of evidence suggests that these centennial‐scale changes in summer SSS may have been driven by solar‐induced changes in the East Asian Monsoon, but further evidence is needed to firmly establish this relationship.  相似文献   

A new standardized Palmer drought index for hydro‐meteorological use          下载免费PDF全文

Mingwei Ma  Liliang Ren  Fei Yuan  Shanhu Jiang  Yi Liu  Hao Kong  Luyan Gong 《水文研究》2014,28(23):5645-5661

Accepting the concept of standardization introduced by the standardized precipitation index, similar methodologies have been developed to construct some other standardized drought indices such as the standardized precipitation evapotranspiration index (SPEI). In this study, the authors provided deep insight into the SPEI and recognized potential deficiencies/limitations in relating to the climatic water balance it used. By coupling another well‐known Palmer drought severity index (PDSI), we proposed a new standardized Palmer drought index (SPDI) through a moisture departure probabilistic approach, which allows multi‐scalar calculation for accurate temporal and spatial comparison of the hydro‐meteorological conditions of different locations. Using datasets of monthly precipitation, temperature and soil available water capacity, the moisture deficit/surplus was calculated at multiple temporal scales, and a couple of techniques were adopted to adjust corresponding time series to a generalized extreme value distribution out of several candidates. Results of the historical records (1900–2012) for diverse climates by multiple indices showed that the SPDI was highly consistent and correlated with the SPEI and self‐calibrated PDSI at most analysed time scales. Furthermore, a simple experiment of hypothetical temperature and/or precipitation change scenarios also verified the effectiveness of this newly derived SPDI in response to climate change impacts. Being more robust and preferable in spatial consistency and comparability as well as combining the simplicity of calculation with sufficient accounting of the physical nature of water supply and demand relating to droughts, the SPDI is promising to serve as a competent reference and an alternative for drought assessment and monitoring. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

NLOS GPS signal detection using a dual-polarisation antenna   总被引：2，自引：2，他引：0  

Ziyi Jiang  Paul D. Groves 《GPS Solutions》2014,18(1):15-26

The reception of indirect signals, either in the form of non-line-of-sight (NLOS) reception or multipath interference, is a major cause of GNSS position errors in urban environments. We explore the potential of using dual-polarisation antenna technology for detecting and mitigating the reception of NLOS signals and severe multipath interference. The new technique computes the value of the carrier-power-to-noise-density (C/N ₀) measurements from left-hand circular polarised outputs subtracted from the right-hand circular polarised C/N ₀ counterpart. If this quality is negative, NLOS signal reception is assumed. If the C/N ₀ difference is positive, but falls below a threshold based on its lower bound in an open-sky environment, severe multipath interference is assumed. Results from two experiments are presented. Open-field testing was first performed to characterise the antenna behaviour and determine a suitable multipath detection threshold. The techniques were then tested in a dense urban area. Using the new method, two signals in the urban data were identified as NLOS-only reception during the occupation period at one station, while the majority of the remaining signals present were subject to a mixture of NLOS reception and severe multipath interference. The point positioning results were dramatically improved by excluding the detected NLOS measurements. The new technique is suited to a wide range of static ground applications based on our results.  相似文献   

塔里木盆地苏盖特布拉克剖面寒武系第二统第三阶微生物岩结构类型^*          下载免费PDF全文

李莹  潘文庆  吴亚生  杨果  孙崇浩  姜红霞 《古地理学报》2020,22(4):663-679

塔里木盆地阿克苏地区寒武系第二统第三阶肖尔布拉克组主要由微生物白云岩组成,代表性的剖面在阿克苏市西南90 km处的苏盖特布拉克。由于成岩作用改造严重,对这套微生物碳酸盐岩的特征和形成环境的认识还存在很多分歧,制约了勘探工作。通过详细野外勘察和室内研究,将肖尔布拉克组微生物岩分为4种结构类型: 凝块结构、纹层结构、砂屑结构和骨架结构。首次对凝块结构和纹层结构进行了亚类型的划分,其中凝块结构可划分为蠕虫状、网状和斑点状3种亚类型,纹层结构可划分为致密纹层、短薄纹层、颗粒纹层以及单纹层、纹层组、复合纹层。肖Ⅰ段—肖Ⅲ段发育凝块石白云岩、凝块—层纹石白云岩和层纹石白云岩,肖Ⅳ段发育凝块石微生物丘,肖V段下部发育网状结构凝块石白云岩,肖V段上部发育砂屑白云岩和肾形菌骨架岩。白云石化作用、溶蚀作用、重结晶作用是改变肖尔布拉克组微生物岩结构最重要的成岩作用,且该组下部比上部遭受了更强的成岩作用改造;微生物岩结构对成岩作用改造的抵抗能力为: 砂屑结构>纹层结构>凝块结构。根据微生物岩结构,推测肖Ⅰ段—肖Ⅲ段形成于潮坪环境,肖Ⅳ段和肖V段下部形成于深水潮下环境,肖V段上部形成于浅水潮下环境。以上成果为认识塔里木盆地肖尔布拉克组微生物岩的平面分布规律和今后开展被成岩作用强烈改造的白云岩型微生物岩的研究提供了一个重要参考。  相似文献   

黑龙江省海伦市长发镇土地质量地球化学评价及开发建议     

刘国栋  杨泽  戴慧敏  张一鹤  肖红叶  陈江 《地质与资源》2020,29(6):533-542

基于海伦市长发镇1：1万土地质量地球化学调查获得的土壤重金属元素和养分元素数据，参照土壤环境质量标准（GB15618—2018）和土地质量地球化学评价规范（DZ/T0295—2016），采用单指标评价法对研究区土壤养分和土壤环境质量进行评价，并在此基础上，将两者叠加分析，对研究区进行土地质量地球化学综合判定.结果表明：研究区内土壤养分以丰富及较丰富为主，分别占长发镇总面积的37.49%和62.22%，区内缺乏B、Mo；研究区99.94%的土地为无风险（一等），0.06%的土地为风险可控（二等），风险可控土地主要受Cd及Hg元素的影响；土地质量地球化学综合评价结果显示，研究区以一等（优质）土地为主，占评价区总面积的99.66%；研究发现长发镇富Se土地资源面积19.25 km²，土壤中Se含量为0.4×10^-6～1.4×10^-6，平均值为0.44×10^-6；长发镇符合绿色食品产地的耕地面积138.44 km²，占调查区耕地面积的99.84%，其中绿色富Se、绿色食品产地分别为18.53 km²和119.91 km².  相似文献   

改进的小波阈值函数对变形监测数据的去噪研究     

甘若  陈天伟  郑旭东  段青达  潘梅 《大地测量与地球动力学》2020,40(1):17-22

基于小波分析中传统的阈值函数,结合其他学者提出的小波阈值函数,提出一种改进的小波阈值函数,并将其应用于变形监测数据的去噪处理。理论分析和算例表明,新的小波阈值去噪函数能够有效去除噪声。  相似文献   

GBW10010a大米标准物质复(研)制及数据特征     

杨榕  顾铁新  潘含江  刘妹  周国华 《岩矿测试》2020,39(6):866-877

随着我国对生态文明建设的重视，自然资源综合调查势在必行，对生物标准物质亦提出了新的需求。当前相关调研工作已经大面积开展，自然资源综合调查、农产品与食品安全评价都需要对生物样品元素组成进行准确测试，需要以生物标准物质作为生物成分测试量值比对和溯源的基础，因此对生物基体标准物质的需求量大幅增加。大米作为主要粮食之一，其食品安全日益受到重视，对大米中的化学成分进行准确的分析测试具有重要的现实意义，因而对大米标准物质的需求量尤为突出，但目前大米成分分析标准物质已供不应求。本文严格按照《标准物质定值的通用原则及统计学原理》（JJF 1343—2012）和《地质分析标准物质的研制》（JJF 1646—2017）等相关规范要求，开展了GBW10010a大米成分分析标准物质的复（研）制工作，包括样品采集、加工制备、均匀性检验、稳定性检验、多家实验室协作定值测试及不确定度评定等关键环节。结果表明：本次复（研）制的大米标准物质定值成分多样、量值准确可靠，符合国家一级标准物质的要求。GBW10010a共定值54项主微量元素，包括Ag、Al、As、B、Ba、Be、Bi、Ca、Cd、Ce、Co、Cr、Cs、Cu、Dy、Er、Eu、Fe、Gd、Ge、Hg、Ho、K、La、Li、Ho、Mg、Mn、Mo、N、Na、Nb、Nd、Ni、P、Pb、Pr、Rb、S、Sb、Sc、Se、Si、Sm、Sr、Tb、Th、Tl、Tm、U、V、Y、Yb、Zn，其中的39项元素给出了标准值及不确定度，包括Ag、Al、As、B、Ba、Ca、Cd、Ce、Co、Cs、Cu、Dy、Er、Fe、Hg、K、Li、Mg、Mn、Mo、N、Na、Nd、Ni、P、Pb、Pr、Rb、S、Sb、Se、Si、Sm、Sr、Tb、Tl、Y、Yb、Zn；15项元素提供参考值，包括Be、Bi、Cr、Eu、Gd、Ge、Ho、Ho、La、Nb、Sc、Th、Tm、U、V。与原有GBW10010大米标准物质相比较，GBW10010a中As、Cd、Co、Cr、Cu、Hg、Mn、Mo、Ni、Zn等重金属元素含量显著下降，其中Cd、Cu、Zn降幅较大，分别下降约39%、43%、38.7%，一定程度上反映了农田生态环境的改善。本批标准物质定值元素总数量增加了6项，新增定值元素Ag、Nb（Nb给出参考值），并且各项元素不确定度范围整体上有所缩小，如Al、Cd、Cu、Fe、K、Mg、Mo、Na、P、Pb、Se、Zn等对生物易有影响的重要元素，表明了地质分析测试方法技术的进步及定值水平的提高。本批标准物质定值元素涵盖了具有生物效应的大部分主微量元素，适用于农业生态环境地球化学调查与评价、生物样品测试、农产品质量与食品安全评价样品测试时的分析仪器校正、分析方法评价和分析质量监控等多个领域。  相似文献   

Cold water anomalies in the middle layer of the northern Taiwan Strait in spring—a numerical approach     

Zhao  Zhonghua  Lin  Jianwei  Fu  Jun  Jiang  Yuwu 《Ocean Dynamics》2020,70(12):1571-1585

Ocean Dynamics - Cold water anomalies were found in the middle layer in the northern Taiwan Strait in the spring of 2015. The cold water was located at a depth of approximately...  相似文献