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1.
发射信号不完善性对卫星导航系统内及系统间干扰的影响分析 总被引：1，自引：1，他引：0
研究了3种典型的卫星发射信号不完善性——载波泄漏、互调失真和杂散辐射对于卫星导航信号的接收所带来的干扰,通过信号建模以及谱分离系数、码跟踪谱灵敏度系数和等效载噪比的解析计算对干扰效果进行量化分析;针对GPS和Galileo系统L1/E1频段的信号进行了多层次的仿真计算,给出了综合考虑噪声、信号损耗、外源干扰、GNSS系统内和系统间干扰,以及3种信号不完善性单独作用、两两组合和综合作用下的结果,其中对于GPS L1C/A短码考虑了电文调制对线谱的影响。结果表明,当总的不完善干扰功率水平达到一定程度后,其对接收机信号捕获跟踪和解调的影响大于系统间干扰,不能忽略。 相似文献
2.
Wenxiang ZHANG Shilun YANG Jun ZHU Shiliang GONG Pingxing DING 《国际泥沙研究》2007,22(3):199-207
This paper reports the results of continuous monitoring of turbidity, water depth, salinity (using an Optical Backscatter Sensor (OBS)), and current velocity (using a Current meter (SLC9-2)) in the South Passage of the Changjiang Estuary over a spring–neap period in February 2003 (dry season). The turbidity measured via OBS was closely correlated with the suspended sediment concentration (SSC), which was highly variable. Over the study period, the SSC in the middle layer ranged from 110 to 1400 mg/l. The minimum SSC occurred during a late ebb tide, and the maximum SSC occurred during a late flood tide. On average, the SSC was 1.5 times higher during flood tide than during ebb tide. Vertically within the water column, SSC increased downward, with the ratio of SSC measured near the bed to that measured at the surface ranging from 1.90 to 18.3. The temporal variability in SSC is jointly governed by tides and wind-induced waves, whereas the vertical variability in SSC is attributed to the effect of gravity and vertical water circulation. 相似文献
3.
Estimates of spatial and temporal variations in suspended sand concentrations (SSC) made with a multi-transducer Acoustic Backscatter Sensor (ABS) under a repeated wave group over a mobile rippled bed in the wave research flume at the National Hydraulics Laboratory in Ottawa, Canada, reveal an number of complex and intriguing patterns. Ensemble averages of 8 nearly identical wave groups provided much more robust estimates of SSC and allowed a detailed examination of the wave group effects. The largest SSC near the bed (< 0.10 m) occurs in phase with the largest waves in the group. Above approximately 0.10 m elevation, SSC lags behind the near bed SSC by as much as 2–3 waves; introducing significant curvature (on a semi-log plot) to the SSC profile. The log linear segments of the SSC profile grow and decay systematically on the scale of the wave group. The range in lengths of log-linear profile segments ( 0.03–0.355 m) suggest that the boundary layer thickness also fluctuates throughout the passage of the wave group. Furthermore, there are significant variations in the patterns of SSC, which occur under the largest and smallest waves in the group. Under the largest waves vertical bands of alternating high and low SSC produce an intra-wave modulation in the upper water column ( 0.075–0.30 m). The equivalent horizontal excursion of these bands scales to the ripple length. Under the smaller waves the intra-wave modulation of the SSC disappears and is replaced by temporally homogenous suspension that expands vertically through several individual wave cycles. The former pattern of homogenous suspension appears to be associated with growth of a boundary layer due to the persistent uni-directional horizontal flow during this part of the group together with the persistence of antecedent bed generated turbulence and vorticity which maintains the suspension. The latter pattern of bands of high and low SSC indicates a strong temporal and spatial constraint on the SSC (phase coupling) induced by the presence of the bedforms which may be enhanced by strong reversals in both flow and vorticity under the large waves in the group. 相似文献
4.
杭州湾HJ CCD影像悬浮泥沙遥感定量反演 总被引：6，自引：0，他引：6
利用环境小卫星CCD(HJ CCD)影像对杭州湾悬浮泥沙浓度(SSC)进行了反演研究。通过对杭州湾水体遥感反射率(Rrs)与SSC进行相关性分析发现,在690nm和830nm左右出现显著的反射峰,分别位于HJ CCD影像的第3和第4波段范围内;大于700nm波长处的Rrs与SSC相关性较好。基于实测Rrs和SSC之间的相关关系,利用第4和第3波段比值作为遥感因子建立SSC反演模型,模型决定系数达到0.90。借鉴近红外-短波红外(NIR-SWIR)结合的大气校正方法反演出的准同步MODIS气溶胶数据,实现了HJ CCD影像的大气校正,第3、第4波段的大气校正结果相对误差分别为5.54%和6.97%。结果显示,HJ CCD影像反演的SSC相对误差为7.12%;杭州湾悬浮泥沙浓度要显著高于长江口,且内部差异明显。研究表明,通过适当的大气校正方法和反演算法,HJ CCD影像可用于杭州湾悬浮泥沙浓度的估计。 相似文献
5.
因为具有明显的时间与空间分辨率优势,遥感数据成为近岸Ⅱ类水体悬浮泥沙浓度(SSC)信息提取研究的重要数据源之一.悬浮泥沙遥感信息提取的现状可归纳为:(1)建立近岸Ⅱ类水体SSC遥感模式的方法有三种类型,分别是基于地面光谱与SSC测量的反射率反演方法、基于图像信息法和基于大气辐射传输理论模型法;(2)基于地面测量的反射率反演方法属于理论与经验相结合的方法,也是目前用于SSC定量化遥感模式研究的常用方法.其数学表达形式包括线性关系式、对数关系式、负指数关系式、Gordon模式和综合模式等;(3)到目前为止已有的Ⅱ类水体SSC遥感模式适用性方面还不理想,远未达到与试验室分析相匹配的精度.文章认为:加强地面水文光谱实验研究,建立多光谱SSC定量模式,以高分辨率和高光谱遥感融合数据为基础的SSC定量遥感是今后该方向发展趋势. 相似文献
6.
A study of suspended sediment concentration in Yangshan deep-water port in Shanghai,China 总被引：1，自引：0，他引：1
Suspended sediment concentration (SSC) plays an important role in the estuarine environment.Its spatial or temporal variations in coastal zones and estuaries indicate that sediments are suspended,trans... 相似文献
7.
通用地震数据采集器EDAS-24GN中CPU数据收发方式 总被引：1，自引：1，他引：0
通用地震数据采集器EDAS-24GN引入一种新型的数据传输方式,通过AT91SAM9263CPU板带有的同步串行控制器进行数据传输,可以有效解决前一种方式存在的问题.经过实验验证,新型的数据传输方式在每秒传输50 kB数据时,引起的中断次数只有十几次,有效提高了CPU处理效率,且不存在数据丢失现象. 相似文献
8.
基于座底ADCP实测回波强度信号,结合短期实测悬浮体质量浓度,反演长时间序列悬浮体质量浓度,定量分析了渤海湾近一年悬浮体质量浓度变化特征及其影响因素。结果表明:受风浪影响,该区悬浮体质量浓度具有明显季节性变化特征,风浪作用强烈的季节其悬浮体浓度表现为相对高值。悬浮体净输运同样具明显季节性变化,秋冬强风浪作用下,悬浮体的净输运量明显增加;而在不同季节,月净输运方向具有不同的主输运方向。悬浮体质量浓度日变化受潮流控制明显,长周期变化则主要与风场的变化有关。潮流涨急过程与风致大浪过程均可引起沉积物再悬浮,导致悬浮体浓度明显增高。 相似文献
9.
This study analyses the changes in sediment transport regimes in the middle Yellow River basin (MYRB) using sediment rating parameters. Daily streamflow and suspended sediment concentration data were collected at 35 hydrological stations from the 1950s to 2016, which can be divided into three periods based on the type and intensity of human activities: the base stage before 1970, the restraining stage from 1971 to 1989, and the restoration stage after 2002. Data within each period were fitted by log‐linear sediment rating curves and the sediment rating parameters were utilized to analyse the spatial and temporal variations in sediment transport regimes. The results show that sediment rating parameters are indicative of sediment transport regimes. In the base stage and the restraining stage, the hydrological stations can be categorized into four groups based on their locations on the rating parameter plot. The stations with small drainage basins were characterized by the highest sediment transport regime, followed by those located in the coarse‐particle zone, the loess zone, and the mountainous/forest zone. In the restoration stage, the difference in sediment transport regimes between different geomorphic zones became less distinguishable than in previous stages. During the transition from the base stage to the restraining stage, sediment rating parameters showed no significant changes in sediment transport regimes in all four geomorphic groups. During the transition from the restraining stage to the restoration stage, significant changes were observed in the coarse‐particle zone and the mountain/forest zone, indicating that the revegetation programme and large reservoirs imposed a stronger influence on sediment transport regimes in these two zones than in the rest of the MYRB. This study provides theoretical support for evaluating sediment transport regimes with sediment rating parameters. 相似文献
10.
福建近岸悬浮泥沙浓度遥感监测 总被引：2，自引：0，他引：2
本文研究利用遥感技术监测大面积海域的悬浮泥沙浓度(SSC)、综合探究福建近岸SSC的时空变化规律:采用前人通过实测资料建立的福建近岸海域的SSC反演模型,选取不同时相的MODIS数据集,利用IDL&ENVI对福建近岸海域的SSC进行遥感反演,并从SSC的基本分布模式、随潮汐变化、随季节变化和随风场变化等4个方面进行时空变化分析.结果表明,福建近岸海域SSC由近岸向外岸逐渐降低;大潮时的SSC高于小潮时的SSC;福建省三大流域入海处的SSC在秋季最高;此外,SSC的分布受风速和风向的影响很大. 相似文献