共查询到18条相似文献，搜索用时 218 毫秒
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波形分解是机载测深LiDAR数据处理的关键环节,为水深计算、底质类型反演和水体浑浊度分析等提供基础信息。针对传统测深LiDAR波形分解算法受噪声干扰严重、对微弱及叠加信号分解不准确的问题,提出一种新的波形分解算法。对原始波形经小波滤波后,计算滤波前后尾段波形的差异,估计回波信号的噪声;利用高斯模型,从原始波形数据中不断分解出经LM算法优化参数后的波形分量,直到剩余波形中最大峰值与优化后的参数小于一定阈值。通过南海实测数据进行验证,实验结果表明:该算法分解弱回波能力强,不论在浅水(回波发生叠加)还是深水,其分解精度均优于传统算法。 相似文献
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漫衰减系数是一个重要的海洋光学参数,能够为水体环境变化、水质分析以及水产养殖等方面提供基础性数据。针对目前船载实地测量效率与分辨率低、卫星遥感反演精度与分辨率较低的局限性,本文提出一种基于机载LiDAR测深水体波形的漫衰减系数提取方法。该方法首先通过分层异构模型的机载LiDAR波形分解算法得到水体散射回波,利用激光在水体中的衰减特性,构建漫衰减系数提取模型,最终获取大面积水域漫衰减系数的空间分布。采用西沙甘泉岛与江苏连云港两个航次的实测数据对所提算法进行了验证,本算法无需每个测深点的水底底部回波强度和深度即可反演得到漫衰减系数,并且在浑浊水域也可取得较好的效果,表明在中国近海利用机载LiDAR测深系统能够有效获取高精度的漫衰减系数。 相似文献
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针对双频测深激光雷达数据的特点,研究了利用激光回波波形特征实现点云数据水陆分离的方法。激光和水体的相互作用通常会导致激光回波波形的展宽,与仅在空气中传播的陆地激光回波有明显区别。首先采用高斯函数对回波数据进行波形模拟,用期望方差最大法求解高斯函数的最优参数,得到波形拟合特征参数,随后以绿波段的波宽之和以及红波段与绿波段振幅比值这两个指标作为水陆分离的特征参数,采用最佳阈值分割法得到阈值参数并实现水陆分离,最后采用遥感影像辅助生成准确的水陆点云类别,评价本文方法的分类精度。实验结果表明,基于回波波形特征和阈值分割的方法能够较为准确地实现双频测深激光雷达数据的水陆分离,数据正确率优于94%。 相似文献
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针对全波形三维激光测绘雷达(LiDAR)在数字地形测量中如何降低背景噪声问题,提出了一种基于经验模态分解(EMD)和小波阈值的自适应降噪方法。在扫测的地形信号经EMD分解后,计算内蕴模式函数(IMF)与经过2/3阶重构的扫测信号之间的互相关函数,从而改善小波阈值自适应地对IMF中的高频噪声成分进行滤除。实验结果表明,与EMD重构降噪法、小波阈值降噪法和传统的EMD-小波联合降噪法比较,这种方法在对全波形LiDAR回波信号的噪声剔除和地物信号保留方面具有明显的优势,降噪后信号的误差能缩小10%~20%,波形相关性能提升5%~20%,信噪比能提升20%~40%。 相似文献
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本文基于Amarouche的二阶理论回波模型,导出了带有偏度系数的二阶理论回波模型;针对HY-2A卫星高度计波形特点,引入了奇异值分解滤波,并根据最大似然估计算法反演参数的不同得到6种重跟踪方案;利用其中的五参数方案处理该波形数据,获得海面散射点高度概率密度函数中偏度的合理取值为0.15;将结果分别与浮标、Jason-1和HY-2AIDR有效波高对比,分析6种方案反演有效波高的准确度,确定了MLE4_SVD(波形重跟踪之前进行滤波)对HY-2A高度计重跟踪更适合反演有效波高。 相似文献
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利用回波信号的物理性质代替几何性质,将Darcy渗流方程与非线性扩散方程耦合,提出了一种基于多物理场的信号处理方法,通过有限差分方法进行离散化处理,实现对机载激光测深回波信号的处理。在此基础上,基于激光在海水中的传播特性,建立数学关系式,对机载532 nm激光测深系统回波信号进行数值模拟,利用多物理场信号处理方法对仿真模拟数据进行处理,并与传统滤波方法比较。实验结果表明,该方法可以很好地应用于机载激光回波信号的处理中,通过比较得出多物理场方法精度较高,算法稳定,验证了该方法的可行性与有效性。 相似文献
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基于相关矩阵特征向量的目标分解将地物回波复杂的散射过程分解成相互独立的三种单一散射分量:单向散射、双向散射和交叉散射,分别对应各自的目标相关矩阵。目标分解技术降低了散射回波之间的相关性,有利于分析地物散射机理,有助于提高分类精度。对荷兰F levoland地区全极化数据进行分解,经过试验和相关性分析,选用7种数据形成多参数数据组合,对其进行最大似然监督分类,同时进行常规三种极化加相位差的分类和基于复W ishart分布的最大似然分类,逐像元计算混淆矩阵,分析对比三种分类结果的精度,试验表明:相对于常规数据组合分类,基于复W ishart分布的监督分类可以小幅度提高分类精度,而利用目标分解得到多参数组合数据进行分类则有大幅度的提高。 相似文献
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水声宽带信号波形预报技术研究 总被引：1，自引：0，他引：1
为了实现远程水下目标微弱信号检测,掌握远程传输后信号波形的特征,水声宽带信号波形预报技术是研究水下信号精细化特征研究的重要突破口之一.针对宽带信号,采用波束位移射线简正波(BDRM)频域合成波形预报算法和 BELLHOP 射线时域波形预报算法,获得宽带信号远程波形预报模型,并在浅海负跃层和深海声道两种典型海洋环境下,利用上述两种宽带波形预报算法,仿真计算了宽带信号远程波形,比较了两种波形预报算法精度.结果表明,在一定条件下,两种模型具有同等计算精度,可满足不同条件下的信号波形预报需求. 相似文献
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Surajit Ghosh Praveen Kumar Thakur Vaibhav Garg Subrata Nandy Shivprasad Aggarwal 《Marine Geodesy》2015,38(3):597-613
In the present study, behavior of the SARAL/AltiKa (Satellite with ARgos and ALtiKa) waveforms over Maithon Reservoir (～65 km2 of surface area), Jharkhand, India, has been studied. The estimated water level has been compared with the in situ measurements at hydro-gauging station at the dam site. The problem of minimization of errors in the water level retrieval from AltiKa measurements has been resolved by improvement of the retracking method. A real retracking gate detection algorithm based on statistical analysis harnessing various physical parameters of the waveform has been developed, which has been applied to SARAL/AltiKa waveforms over the Maithon reservoir. Comparing the in-situ measurements with altimetry data (from cycle 1, 19 March 2013 to cycle 12, 8 April 2014) showed that it is crucial to improve the retracking method. Results showed accuracy of water level monitoring increased by nearly 76% by the newly developed waveform retracking algorithm over non-retracked water level. We also compared this new method with the existing ice-1 algorithm and found that with the new method there is improvement of ～27% over ice-1 retracked water level. The correlation coefficient values and root mean square values without retracking, with ice-1 algorithm and with newly developed retracking algorithm were 0.87, 0.91, and 0.95, and 8.12 cm, 2.08 cm, and 1.42 cm, respectively. This shows the proposed retracker performed better than ice-1. The retracking procedure helped in outliers' identification and substitution and with waveform fitting and waveform parameter extraction. This algorithm should have good performance capability for retrieving water level over inland water bodies like Maithon reservoir. 相似文献
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多波束水体数据是多波束系统获取的最原始数据,记录了波束从发射到接收整个过程全部的反向散射强度信息,可以为目标识别、水下栖息环境探测等提供重要的数据支撑。目前,针对多波束水体强度时间序列所表现的波形信息的处理及研究仍处于起步阶段,另外水体波形数据易受噪声影响,且存在明显的入射角效应问题,对此,本文提出了一种基于分区异构的多波束水体波形拟合算法。首先,根据不同波束入射角范围的水体波形特性,将水体数据划分为3个区域;然后利用不同函数(中央波束区域—双指数函数、漫反射区域—广义高斯与线性函数叠加、边缘波束区域—高斯与多项式叠加)分别对不同分区的反向散射强度波形进行拟合。采用台湾海峡的多波束水体数据进行验证,结果表明:不同分区拟合相关系数及拟合优度均达到0.95以上,相比简单函数拟合,均方根误差由3.39 dB降到1.5 dB以下,达到了较好的拟合效果,可为多波束水体目标识别和海底分类提供参考。 相似文献
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In this study, a waveform retracking algorithm based on finding the inflection-point of the waveform is proposed. After two-steps pre-processing procedure, we employ this method for 145 cycles of Jason-2 data for two tracks 81 and 16 over the Strait of Hormuz. Moreover, we obtain the corrected SSH by the common empirical methods namely Offset Centre of Gravity, Beta and Threshold as well as the ALES. We compare the SSH time series from proposed algorithm with those from common empirical methods. Results are validated against three nearby tide-gauges in the case study. The correlation coefficient and RMSE between the corrected SSH and tide-gages data were computed for three distance classes from the coastline: 0～5, 5～10 and 10～15 kilometer. Our method improves the averaged RMSE of raw SSH up to 41%, 41% and 24%, for these classes over track 81 and 51%, 38% and 41% over track 16, respectively. The averaged correlation values of the proposed method indicate 33%, 11% and 2% improvement over track 81 and are 29%, 14% and 3% over track 16 for three distance groups, respectively. Our method leads to slightly better results than the successful ALES method, especially within the range of 0～5 km. 相似文献
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The major drawback of Ka band, operating frequency of the AltiKa altimeter on board SARAL, is its sensitivity to atmospheric liquid water. Even light rain or heavy clouds can strongly attenuate the signal and distort the signal leading to erroneous geophysical parameters estimates. A good detection of the samples affected by atmospheric liquid water is crucial. As AltiKa operates at a single frequency, a new technique based on the detection by a Matching Pursuit algorithm of short scale variations of the slope of the echo waveform plateau has been developed and implemented prelaunch in the ground segment. As the parameterization of the detection algorithm was defined using Jason-1 data, the parameters were re-estimated during the cal-val phase, during which the algorithm was also updated. The measured sensor signal-to-noise ratio is significantly better than planned, the data loss due to attenuation by rain is significantly smaller than expected (<0.1%). For cycles 2 to 9, the flag detects about 9% of 1Hz data, 5.5% as rainy and 3.5 % as backscatter bloom (or sigma0 bloom). The results of the flagging process are compared to independent rain data from microwave radiometers to evaluate its performances in term of detection and false alarms. 相似文献
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Retracking altimeter waveforms over inland water bodies is a challenging task as a wide range of waveform is encountered while the retracking algorithms are available only for a handful of echo shapes. One such waveform shape widely encountered in lakes and reservoirs is the multipeak echo. These echoes are produced when the interacting surface in the altimeter footprint is not homogeneous and a number of different types of surfaces contribute to the resulting waveform. The widely used conventional retrackers, namely the Brown, Beta-5, Ice-2, OCOG, and threshold, can retrack a number of different waveform shapes such as the Brown like waveforms, specular waveforms, and rectangular waveforms but may not perform well for multipeak waveforms. In this article, a technique has been demonstrated to identify the different subwaveforms within a multipeak waveform and identify the subwaveform corresponding to the target at nadir. The subwaveform that is reflected from the nadir surface is identified from apriory information about the surface topography of the area. The subwaveform is then retracked using the 50% threshold to find the correct retracked range and water height. This technique has been tested for nine cycles of SARAL SIGDR data on Ukai reservoir, Gujarat, India, and found to perform much better than the other retrackers, particularly for multipeak waveforms. 相似文献
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针对基于MEMS加速度传感器的空投波浪浮标存在采样频率与测波精度低的问题，根据频域衰减积分算法，提出一种相应的波浪测量算法，为了验证该算法测波的准确性，开展了多功能水槽试验研究。该算法旨在将MEMS加速度传感器输出的加速度与姿态角转化为浮标运动的波形，首先将加速度与姿态角信号进行竖向处理获得竖直方向的加速度，再利用离散傅里叶变换将竖向加速度转化为频域内的加速度复数序列，然后引入控制函数减弱低频噪声，经过频域积分、离散傅里叶逆变换、时域积分获得竖直方向的位移，最后通过后处理得到最终的波形。多功能水槽试验采取10中不同波高和周期的工况，对比空投波浪测量浮标与波高仪的测量结果，试验结果表明，浮标的测量误差在10%以内，达到测波标准。 相似文献
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全球日益增多的海滩垃圾，不仅造成海洋环境污染，严重威胁海洋生态系统健康，也对生物栖息地有着不可估计的影响。如何高效准确地对海滩垃圾进行监测和识别，是处置海滩垃圾过程的技术难点之一。基于此，本文以长江口南汇边滩为实验区，通过在海滩上设置常见垃圾样品，随后利用激光雷达记录的全波形数据和BP神经网络模型，以快速鉴别海滩垃圾类型。结果表明:基于激光雷达提取的垃圾全波形数据中回波振幅和回波宽度的差异，可用来识别海滩垃圾。构建的BP神经网络可有效将海滩垃圾分为泡沫类、布类、金属类、纸类及塑料类，最高识别率达到79%。此外，由于不同材质海滩垃圾的原材料成分存在相似或同质，会对精确识别区分垃圾类型造成一定的干扰，从而影响神经网络的识别率。可见，将激光雷达应用于识别海滩垃圾，为海滩垃圾的监测提供了新的方法。 相似文献