长山群岛海洋渔业资源的平均营养级变化特征     

孙才志  曹威威  肖春柳 《海洋通报》2019,38(1):87-95

根据长山群岛 1965-2016 年渔业统计资料，分析长山群岛海域主要捕捞渔获物产量、平均营养级 （Mean trophic level， MTL）、渔业均衡指数 （Fishing in balance index，FiB） 年际变化，探讨其海洋渔业资源利用状况，并利用小波分析方法研究52年来渔获物 MTL 周期变化特征。研究表明： （1） 长山群岛捕捞产量、MTL 和 FiB 指数呈阶段性变化； （2） 长山群岛渔业资源开发经历初期开发、扩张捕捞、过度捕捞、资源破坏等四个阶段，渔业资源环境正在逐渐恶化；（3） 受人类捕捞活动影响，MTL 在 15~19 年和 24~34 年两种时间尺度下呈周期波动，30 年为第一主周期，17 年为第二主周期。长山群岛渔业资源破坏日益严重，未来几年平均营养级将呈下降趋势。为防止渔业资源进一步衰退，应加强捕捞活动管理力度，落实海洋渔业资源保护制度；完善预警机制，构建海洋渔业资源监测系统；同时应积极调整长山群岛渔业产业结构，提高资源产出效率.  相似文献   

A physically constrained wavelet-aided statistical model for multi-decadal groundwater dynamics predictions     

Fatih Gordu  Mahmood H. Nachabe 《水文研究》2021,35(8):e14308

A physically constrained wavelet-aided statistical model (PCWASM) is presented to analyse and predict monthly groundwater dynamics on multi-decadal or longer time scales. The approach retains the simplicity of regression modelling but is constrained by temporal scales of processes responsible for groundwater level variation, including aquifer recharge and pumping. The methodology integrates statistical correlations enhanced with wavelet analysis into established principles of groundwater hydraulics including convolution, superposition and the Cooper–Jacob solution. The systematic approach includes (1) identification of hydrologic trends and correlations using cross-correlation and multi-time scale wavelet analyses; (2) integrating temperature-based evapotranspiration and groundwater pumping stresses and (3) assessing model prediction performances using fixed-block k-fold cross-validation and split calibration-validation methods. The approach is applied at three hydrogeologicaly distinct sites in North Florida in the United States using over 40 years of monthly groundwater levels. The systematic approach identifies two patterns of cross-correlations between groundwater levels and historical rainfall, indicating low-frequency variabilities are critical for long-term predictions. The models performed well for predicting monthly groundwater levels from 7 to 22 years with less than 2.1 ft (0.7 m) errors. Further evaluation by the moving-block bootstrap regression indicates the PCWASM can be a reliable tool for long-term groundwater level predictions. This study provides a parsimonious approach to predict multi-decadal groundwater dynamics with the ability to discern impacts of pumping and climate change on aquifer levels. The PCWASM is computationally efficient and can be implemented using publicly available datasets. Thus, it should provide a versatile tool for managers and researchers for predicting multi-decadal monthly groundwater levels under changing climatic and pumping impacts over a long time period.  相似文献   

球面小波模型在GPS高程拟合中的应用     

周贻港  孙罗庆  李中洲 《测绘通报》2020,(12):97-100

本文利用某地共99个GPS水准点的大地高和正常高求取高程异常，使用DOG球面小波模型和多面函数，分别对高程异常进行拟合。拟合时剔除模型残差大于2倍中误差的点，并在剔除粗差后重新进行拟合。通过比较外部检核点的已知高程异常值和球面小波模型值、多面函数拟合值之间的均方差评价模型的精度。数据结果表明，以外部检核均方差最小为准则，球面小波模型拟合精度较优，其拟合精度为1.65 cm，多面函数拟合精度为2.35 cm。  相似文献   

基于小波变换的射频干扰消除方法的研究          下载免费PDF全文

林天琪  吴亚军  朱人杰  徐志骏 《天文学报》2021,62(3):29

在射电天文观测中,射频干扰(Radio Frequency Interference, RFI)会以多种形式混入望远镜接收系统,给观测带来误判或者降低观测信噪比.近年来国内国际射电天文快速发展,国内国际大型射电望远镜和阵列先后建设,观测灵敏度大为提高,射频干扰的影响尤为突出.随着科技发展和人类活动的加剧,射频干扰日益严重且不可逆转.提出利用2维离散小波变换的方法分析射电天文观测的数据,对望远镜系统输出的时间频率序列进行小波变换,根据小波系数分离出原始信号中各分量,每个分量统计得到相应的阈值,将各分量与阈值相比较识别干扰成分并标记去除.利用该方法对实际观测数据进行了处理,结果表明该方法能够很好地标记并消减干扰信号,且提高了观测的信噪比.  相似文献   

复杂环境下地基SAR粗差探测及应用     

马金玉  龙四春  童爱霞  吴文豪  祝传广 《测绘通报》2020,(2):43

雷达视线受施工机械等的间断遮挡导致部分影像产生相位奇异值，从而造成解缠错误及误差传递，简单的相关影像处理难以识别受遮挡影像。本文提出了改进的基于小波变换的信号奇异性检测方法，通过对地基SAR PS点时序相位特征进行分析，将遮挡影像识别转化为粗差探测问题；由PS点相位序列与影像位置关系，根据测区PS点相位序列的奇异点集合得到受遮挡影像集；最后将受遮挡影像剔除后得到的地基SAR监测结果与精密全站仪、水准与游标卡尺数据进行对比分析。结果表明：本文提出的方法用于受遮挡影像的识别是可行的，解决了地基SAR在实际工程应用中可能存在的影像遮挡带来的测量数据含有粗差的问题，提高了监测区域伪影像检测的效率与准确性。  相似文献   

南海北部海域油气资源调查技术及其应用研究——震源子波检测及模拟分析          下载免费PDF全文

曾宪军  翟继锋  韦成龙 《海洋技术学报》2019,38(2)

在野外采集中考察气枪的稳定性以及室内进行确定性子波反褶积处理,都要求能够获得气枪阵列的实时远场子波。从震源子波检测方法出发,阐述了近场子波采集、幅值转换及记录流程,并列举出实测近场子波时需要考虑解决的问题;接着介绍了震源远场子波的获取方法和主要途径;震源近场子波及远场子波的实测方案,检测震源子波所需的仪器设备和采集技术方法。文中分析了气枪子波的气泡干扰问题,虚反射与后续气泡震荡间的关系以及吸收衰减对子波的影响,并根据实测远场子波,对齐氏和范氏两种气体模型进行了模拟效果对比,结果表明:采用范氏气体模型所模拟的子波与实际子波更为吻合,模拟出的气枪的子波波形、振幅大小、气泡周期上,与业界通用的Nucleus软件的模拟结果吻合较好,在后续的使用中将继续优化。  相似文献   

A New Wavelet Method for Identification of Eddies and Assessment of Incidents on Islands of the Eastern Caribbean     

Jason D. Tambie  Madiha Farag-Miller  Keith Miller  Bheshem Ramlal  Michael Sutherland 《Marine Geodesy》2019,42(3):227-245

Using two dimensional continuous wavelet transforms, a novel method for identification of mesoscale eddies is presented to facilitate extraction of characteristics for area, amplitude, type, and location from maps of sea level anomalies. In comparison with the previously established growing method for eddy identification, it is found that the wavelet method identifies more than twice the number of eddies and is particularly better at resolving small eddies down to the 0.25 degree resolution of the data. Such research into eddy identification and tracking is significant to the assessment of eddies with potential to impact on coastlines of small islands. The method is applied to the identification of eddies on tracks towards islands of the Eastern Caribbean over 23?years. Spatial and temporal variation in rate of occurrence and magnitude is established. For Barbados there is an average of 9 anticyclonic incidents a year with maximum amplitude of typically 0.22?m in the dry seasons and 0.16?m in the wet seasons. Seasonal variation is reversed for the other islands with twice the number of anticyclonic incidents having maximum amplitudes of about 0.20?m annually.  相似文献   

Evaluation of nonlinear models for precipitation forecasting     

Abazar Solgi  Vahid Nourani  Mohammad Bagherian Marzouni 《水文科学杂志》2017,62(16):2695-2704

Prediction of factors affecting water resources systems is important for their design and operation. In hydrology, wavelet analysis (WA) is known as a new method for time series analysis. In this study, WA was combined with an artificial neural network (ANN) for prediction of precipitation at Varayeneh station, western Iran. The results obtained were compared with the adaptive neural fuzzy inference system (ANFIS) and ANN. Moreover, data on relative humidity and temperature were employed in addition to rainfall data to examine their influence on precipitation forecasting. Overall, this study concluded that the hybrid WANN model outperformed the other models in the estimation of maxima and minima, and is the best at forecasting precipitation. Furthermore, training and transfer functions are recommended for similar studies of precipitation forecasting.  相似文献   

Particle‐size evidence of barrier estuary regime as a new proxy for ENSO climate variability          下载免费PDF全文

David W. Clarke  John F. Boyle  Andrew J. Plater 《地球表面变化过程与地形》2017,42(10):1520-1534

We investigate a new proxy for ENSO climate variability based on particle‐size data from long‐term, coastal sediment records preserved in a barrier estuary setting. Corresponding ~4–8 year periodicities identified from Wavelet analysis of particle‐size data from Pescadero Marsh in Central Coast California and rainfall data from San Francisco reflect established ENSO periodicity, as further evidenced in the Multivariate ENSO Index (MEI), and thus confirms an important ENSO control on both precipitation and barrier regime variability. Despite the fact that barrier estuary mean particle size is influenced by coastal erosion, precipitation and streamflow, balanced against barrier morphology and volume, it is encouraging that considerable correspondence can also be observed in the time series of MEI, regional rainfall and site‐based mean particle size over the period 1871–2008. This correspondence is, however, weakened after c.1970 by temporal variation in sedimentation rate and event‐based deposition. These confounding effects are more likely when: (i) accommodation space may be a limiting factor; and (ii) particularly strong El Niños, e.g. 1982/1983 and 1997/1998, deposit discrete >cm‐thick units during winter storms. The efficacy of the sediment record of climate variability appears not to be compromised by location within the back‐barrier setting, but it is limited to those El Niños that lead to barrier breakdown. For wider application of this particle size index of ENSO variability, it is important to establish a well‐resolved chronology and to sample the record at the appropriate interval to characterize deposition at a sub‐annual scale. Further, the sample site must be selected to limit the influence of decreasing accommodation space through time (infilling) and event‐based deposition. It is concluded that particle‐size data from back‐barrier sediment records have proven potential for preserving evidence of sub‐decadal climate variability, allowing researchers to explore temporal and spatial patterns in phenomena such as ENSO. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

基于解析信号重构的同步挤压小波变换的时频谱影响因素分析          下载免费PDF全文

游龙庭  宋建国  于会臻  王月蕾 《CT理论与应用研究》2017,26(3):267-278

受测不准原理的制约,小波变换、S变换等时频分析算法无法同时获得高时间分辨率和高频率分辨率。为了满足更高的要求,出现了一种联合小波变换和时频谱重组的新方法—同步挤压小波变换。本文从同步挤压小波变换和基于解析信号重构的同步挤压小波变换的原理出发,通过模型分析算法中参数设置对时频分析结果的影响,包括小波母函数、小波母函数的参数选择和小波阈值等,分析瞬时频率变化率不为零的信号所存在的时频谱模糊现象,并通过控制小波母函数、小波母函数参数以及小波阈值有效地减轻瞬时频率变化率不为零的信号所存在的时频谱模糊现象,时频谱的质量得到一定程度的提高。研究结果对获取高分辨率地震时频谱具有一定的指导意义。   相似文献