基于双树复数小波的SAR图像噪声抑制

小波变换由于其良好的时频分离特性以及接近人类视觉系统的多分辨分析,在SAR图像的去噪和复原中得到了很好的应用,但是经典小波变换不具备平移不变性,且得到的高频分量的方向非常有限.复数小波变换是一种具有近似平移不变性、更多方向选择性且能够完全重构的双数正交小波变换,在图像去噪方面表现出更强的性能.建立了复数小波变换分解与重构的过程,并对分解后的实部和虚部图像的高频部分分别进行局部非线性软阈值法滤波.实验结果显示,复数小波变换较小波变换不仅滤除了更多的噪声,而且得到的图像边缘更加平滑.     

一种利用影像多尺度特征的DOM不可见水印方法

数字正射影像是测绘地理信息服务的基础数据之一。根据生产单位数据现状和对遥感影像数字水印的需求,本文综合利用影像的光谱、纹理和属性特征,提出了利用影像多尺度特征的DOM不可见水印方法。该方法首先结合小波分解和Harris特征算子提取影像多尺度特征,确定多水印的最佳嵌入区域;再利用扩频化的DWT算法嵌入不可见数字水印;最后利用影像属性信息辅助提取水印。本文从主观分析、客观分析和鲁棒性分析3个方面评价了嵌入水印影像,分析结果表明,该方法能够自动、有效地在DOM上嵌入多个不可见数字水印,多水印嵌入和影像属性信息相结合提取水印的策略极大提高了水印鲁棒性和水印检测成功率,可以满足实际生产对水印不可见性、安全性、高效性和鲁棒性的要求。     

新疆喀默什特地区隐伏断裂高精度磁测解释

喀默什特南部戈壁覆盖区存在东西向正磁异常带,长约11km,在进行高精度磁法测量后推测为基性或超基性物质反磁化的反映。为了给出正磁异常带合理的解释,沿异常带垂直方向布设1：10000剖面,通过离散小波分解对剖面磁测数据进行精细化处理,得到不同深度范围内异常的分布。结合欧拉反褶积运算、归一化总梯度处理及空间域解析延拓进一步判断异常特征,发现该异常主要由断裂引起,为塔什纳拉他乌推覆体所引起的断裂在喀默什特南部的延伸段。     

一维小波变换在侧扫声纳图像去噪中的应用

针对侧扫声纳呯信号中的斑点噪声问题,采用一维离散小波变换对信号在各尺度分解,采用非极大值抑制技术平滑信号,并对各层小波系数模极大值进行阈值化处理抑制噪声,讨论了不同阈值对去噪效果的影响。结果表明,尺度因子和阈值的选择对原数据能量保持影响不大,但对噪声抑制效果影响大。文中算例均能较好地保持边缘,边缘保持指数均在0.5以上。     

基于双树复数小波的SAR图像噪声抑制

小波变换由于其良好的时频分离特性以及接近人类视觉系统的多分辨分析,在SAR图像的去噪和复原中得到了很好的应用,但是经典小波变换不具备平移不变性,且得到的高频分量的方向非常有限。复数小波变换是一种具有近似平移不变性、更多方向选择性且能够完全重构的双数正交小波变换,在图像去噪方面表现出更强的性能。建立了复数小波变换分解与重构的过程,并对分解后的实部和虚部图像的高频部分分别进行局部非线性软阈值法滤波。实验结果显示,复数小波变换较小波变换不仅滤除了更多的噪声,而且得到的图像边缘更加平滑。     

Responses of phreatophyte transpiration to falling water table in hyper-arid and arid regions,Northwest China

Quantitative assessment of the impact of groundwater depletion on phreatophytes in (hyper-) arid regions is key to sustainable groundwater management. However, a parsimonious model for predicting the response of phreatophytes to a decrease of the water table is lacking. A variable saturated flow model, HYDRUS-1D, was used to numerically assess the influences of depth to the water table (DWT) and mean annual precipitation (MAP) on transpiration of groundwater-dependent vegetation in (hyper-) arid regions of northwest China. An exponential relationship is found for the normalized transpiration (a ratio of transpiration at a certain DWT to transpiration at 1 m depth, T_a*) with increasing DWT, while a positive linear relationship is identified between T_a* and annual precipitation. Sensitivity analysis shows that the model is insensitive to parameters, such as saturated soil hydraulic conductivity and water stress parameters, indicated by an insignificant variation (less than 20% in most cases) under ± 50% changes of these parameters. Based on these two relationships, a universal model has been developed to predict the response of phreatophyte transpiration to groundwater drawdown for (hyper-) arid regions using MAP only. The estimated T_a* from the model is reasonable by comparing with published measured values.© 2021 China Geology Editorial Office.     

Towards long-multitemporal change detection using SVI differencing by integrated DWT–ISOCLUS: a model for forest temporal dynamics mapping

Abstract

Characterisation and mapping of land cover/land use within forest areas over long-multitemporal intervals is a complex task. This complexity is mainly due to the location and extent of such areas and, as a consequence, to the lack of full continuous cloud-free coverage of those large regions by one single remote sensing instrument. In order to provide improved long-multitemporal forest change detection using Landsat MSS and ETM + in part of Mt. Kenya rainforest, and to develop a model for forest change monitoring, wavelet transforms analysis was tested against the ISOCLUS algorithm for the derivation of changes in natural forest cover, as determined using four simple ratio-based Vegetation Indices: Simple Ratio (SR), Normalised Difference Vegetation Index (NDVI), Renormalised Difference Vegetation Index (RDVI) and modified simple ratio (MSR). Based on statistical and empirical accuracy assessments, RDVI presented the optimal index for the case study. The overall accuracy statistic of the wavelet derived change/no-change was used to rank the performances of the indices as: RDVI (91.68%), MSR (82.55%), NDVI (79.73%) and SR (65.34%). The integrated discrete wavelet transform–ISOCLUS (DWT–ISOCLUS) result was 42.65% higher than the independent ISOCLUS approach in mapping the change/no-change information. The methodology suggested in this study presents a cost-effective and practical method to detect land-cover changes in support of decision-making for updating forest databases, and for long-term monitoring of vegetation changes from multisensor imagery. The current research contributes to Digital Earth with regards to geo-data acquisition, data mining and representation of one forest systems.     

一种率失真最优的JPEG2000码率自适应控制算法

为解决高分辨率航测图像数据量庞大问题,在研究JPEG2000码率控制算法的基础上,提出一种新的码率预分配自适应控制算法.对图像进行小波分解后,将去除最低频的子带小波系数建模为高斯分布.基于率失真理论推导出每个码块在总码率一定的情况下编码中实际应当贡献的码率,在熵编码时实时截止,而对最低频子带进行完整无失真编码.该算法实...     

新疆喀默什特地区隐伏断裂高精度磁测解释简

喀默什特南部戈壁覆盖区存在东西向正磁异常带,长约11km,在进行高精度磁法测量后推测为基性或超基性物质反磁化的反映。为了给出正磁异常带合理的解释,沿异常带垂直方向布设1∶10000剖面,通过离散小波分解对剖面磁测数据进行精细化处理,得到不同深度范围内异常的分布。结合欧拉反褶积运算、归一化总梯度处理及空间域解析延拓进一步判断异常特征,发现该异常主要由断裂引起,为塔什纳拉他乌推覆体所引起的断裂在喀默什特南部的延伸段。     

具有图像内容保持特性的小波域可见水印

根据图像的噪声掩蔽性设计了一种小波域可见水印算法，并根据水印图像的纹理特征对算法作了进一步改进。在此基础上，提出了具有内容保持的嵌入策略及改进算法。实验结果表明，该算法在保证水印具有较好可见性的同时，载体图像内容得到了保持。