采用变系数回归模型提取GPS坐标序列季节性信号

提出采用变系数回归模型提取连续GPS坐标序列中包含的振幅时变季节性信号。对模拟数据及实际GPS坐标序列两组数据的分析结果表明,变系数回归模型在提取GPS坐标序列季节信号方面比传统模型更有效。经处理,GPS坐标序列能获得更合理的速度及噪声估计。     

滇东北地区地震弱活动前兆异常特征研究

以鲁甸M_S6.5地震震中附近的鲁甸大坪子泉水氡、 水质观测资料为基础, 通过对其地震前后的异常特征进行差异性对比, 分析认为震前地震活动丛集, 水氡、 水质异常持续时间较长, 幅度较大, 表现为破年变异常现象; 震后为小震群弱活动, 水氡、 水质异常幅度相对较小, 持续时间较短, 多次出现同步转折, 表现为介质弱化区的前兆异常特征。 从水样测试结果, GNSS位移观测资料、 GPS时间序列曲线及地震活动性等方面分析了鲁甸水氡、 水质的异常机理, 认为鲁甸的水质离子组分群体异常, 与区域的变形活动有关, 局部应力的不断积累, 加剧了地下深部物质活动及构造活动; 近期的同步转折现象属于介质弱化区应力调整状态下的前兆异常。     

高动态宽带信号码跟踪方法仿真分析

针对高动态场景,单独的码环路很难实现跟踪,由于高动态载波跟踪的算法很成熟,通常应用载波跟踪结果对码环路进行辅助,针对窄体制信号,这种方法可以帮助消除码环的动态误差,但对宽体制信号来说,辅助力度减小。从高动态宽带信号码跟踪误差门限以及跟踪精度入手,分析了单独码跟踪算法的易失锁性,理论和仿真验证应用高动态载波跟踪结果辅助码跟踪算法的有效性,且具有高的跟踪精度。这为导航接收机的跟踪算法提供了理论依据。     

Anomalous Signals Prior to Wenchuan Earthquake Detected by Superconducting Gravimeter and Broadband Seismometers Records

Using 1 Hz sampling records at one superconducting gravimeter(SG) station and 11 broadband seismometer stations,we found anomalous signals prior to the 2008 Wenchuan(汶川) earthquake event.The tides are removed from the original SG records to obtain the gravity residuals.Applying the Hilbert-Huang transform(HHT) and the wavelet analysis to the SG gravity residuals leads to time-frequency spectra,which suggests that there is an anomalous signal series around 39 h prior to the event.The period and the magnitude...     

Early-indicator signals of groundwater contamination: the case of seawater encroachment

 An early indication of groundwater contamination occurs when pollutant concentrations start to fluctuate and exceed background values of ambient fresh groundwater. An analysis of a characteristic situation of this type uses data from Israel's coastal phreatic granular aquifer. The pollutant is generally seawater, and the contamination process involves replacement of freshwater by encroaching sea- or other saltwater, a process augmented by human activity. The contamination process involves three stages: (1) groundwater composition remains relatively stable with small salinity content; (2) small salinity changes are perceptible with reversible fluctuations; and (3) salinity concentration increases at a sharply higher rate. The second stage is a useful early-indicator signal of contamination. Early-indicator signals of groundwater pollutant concentrations involve "minor" fluctuations in water chemistry at the advent of the contamination process. The intensity and magnitude of such a salinization/pollution process at any given location depends upon lithologic matrix, aquifer heterogeneity, and resultant flow domain characteristics, as well as contaminant properties. If such "signs" are detected at a sufficiently early stage, appropriate management steps may be taken to rectify further seawater and/or saltwater encroachment. Received: 23 July 1996 · Accepted: 25 June 1997     

关于频率电磁测深几个问题的探讨(八)——频率电磁测深与瞬变电磁测深的关系

从探测原理出发,说明人工源频率电磁测深与瞬变电磁测深的关系密切,这是一个问题的两个方面,可以互相转换。两种探测方法实质是一样的,具有共性;但毕竟从频率域和时间域两个侧面反映问题,又具有各自特性。两种方法的原理所依据的麦克斯韦方程,其正演公式可通过傅立叶变换相互转换;从实际探测所发收的信号特征,场区划分与探测深度等主要方面阐明两种探测方法异同,以加深对探测理论与方法的认识,结合实际择优应用。     

Application of the normalized surface magnetic charge model to UXO discrimination in cases with overlapping signals

This paper presents an application of the normalized surface magnetic charge (NSMC) model to discriminate objects of interest, such as unexploded ordnance (UXO), from innocuous items in cases when UXO electromagnetic induction (EMI) responses are contaminated by signals from other objects. Over the entire EMI spectrum considered here (tens of Hertz up to several hundreds of kHz), the scattered magnetic field outside the object can be produced mathematically by equivalent magnetic charges. The amplitudes of these charges are determined from measurement data and normalized by the excitation field. The model takes into account the scatterer's heterogeneity and near- and far-field effects. For classification algorithms, the frequency spectrum of the total NSMC is proposed and investigated as a discriminant. The NSMC is combined with the differential evolution (DE) algorithm in a two-step inversion procedure. To illustrate the applicability of the DE–NSMC algorithm, blind test data are processed and analyzed for cases in which signals from nearby objects frequently overlap. The method was highly successful in distinguishing UXO from accompanying clutter.     

1971—2020年江西暴雨预警信号等级时空分布特征

利用1971—2020年江西省83站国家气象观测站逐时降水资料,采用EOF分析、Mann-Kendall突变检验、滑动t检验、Morlet小波变换等方法,对江西暴雨预警信号等级的时空分布特征进行了分析。结果表明：1)江西暴雨蓝色、黄色和橙色预警信号年平均发布频次均呈“东北多、西南少”的地域分布,暴雨红色预警主要在鄱阳湖南侧存在多发区;上饶市和景德镇市是暴雨蓝色和黄色预警信号发布频次异常的敏感区,且在江西北部与中部表现出较明显的反位相变化特征。2)暴雨蓝色预警信号发布时间表现为单峰型,主要出现在13—16时,其他三种级别暴雨预警信号发布时间均表现为双峰型,主要有上午和傍晚两个易发时段。3)暴雨红色预警信号发布主要在6—8月,其他等级暴雨预警主要在5—8月,各等级暴雨预警信号均在6月发布最多。4)各等级暴雨预警信号发布频次均存在6—8 a的年际周期振荡,目前江西暴雨蓝色和黄色预警信号发布频次进入偏少期,而暴雨橙色和红色预警信号发布进入偏多期。5)暴雨红色预警信号发布频次呈0.70次/(10 a)的线性增加趋势,且在1992年发生明显由偏少转为偏多的突变,大部地区暴雨红色预警信号发布时降水极...     

内蒙古冬季极端多雪气候事件环流演变特征及季节预测信号

文章研究关注了内蒙古冬季极端多雪气候事件的季节预测问题,在对大量降水观测资料、海温及大气环流场资料进行统计、分析、研究的基础上,确定了历史上58a(1960—2017年)内蒙古冬季极端多雪和少雪气候事件样本,通过对大气环流场的对比分析发现极端多雪或少雪冬季环流场特征显著不同,分析后确定了影响内蒙古冬季降雪的主要环流系统,包括西太平洋副热带高压、极涡、东亚大槽、环流E型及南方涛动等系统。同时,探索了对这些主要环流系统具有预测意义的来自海洋和大气场的预测信号,对预测信号关键区做了标准化定量提取,确定了预测信号综合指数分段判别阈值,给出了预测概念模型,取得了较好预测效果。     

我国西南地区地面和低层大气臭氧的观测分析

本文介绍了1987—1989年在以重庆、成都和贵阳三地区为代表的西南地区进行了地面和低层大气臭氧的观测结果,给出了该地区大气臭氧时空分布的一些特征.分析表明,成都、重庆和贵阳等地区O_3浓度的时空分布及变化规律不尽相同,但都与前体污染物特征以及日照强度、大气层结稳定度.天气过程等密切相关.