共查询到20条相似文献，搜索用时 31 毫秒
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This letter generalizes Pentland's result about the fractal dimension of the optical image of rough natural surfaces, without imposing his requirement that the reflection is Lambertian. Instead, it is assumed that the reflectance coefficient is proportional to the focusing/defocusing due to local surface curvature. It will be proved for this case that the density distribution across the optical image inherits the fractal dimension of the mapped surface. 相似文献
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基于混合像元的方法,利用ERS风散射计(WSC)数据估算植被覆盖率和同时期NDVI有较高的相关性(0.78),计算出的垂直入射菲涅耳反射系数的空间分布状况也比较合理。 相似文献
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LiDAR回波强度数据的校正处理可以提升其在地物分类识别方面的利用价值。本文研究发现倾斜地物(如三角形、拱形房顶等)的自身倾角会改变激光反射角进而影响回波强度,而现有归一化校正模型缺乏对地物倾角的计算分析。随后结合LiDAR数据的采集方式和特点,以及倾斜地物的结构特征,提出了一种加入地物倾角计算的改进型归一化校正算法。首先,对激光点的回波强度值进行基于传输距离值的初步校正;然后,以平面距离值、高程、回波强度值差异为参考,判定激光点是否属于同一倾斜地物,若满足条件,则计算出激光点的趋势角,并依据制定的判定规则确定趋势角的正负;最后,将趋势角计算结果与扫描角数值结合计算出对应的反射角,并重新对回波强度值进行计算校正。实验表明,蓝铁皮材质的三角形、拱形房顶的回波强度值范围和均方差缩小,且采集的8种地物样本的回波强度均值的差异性与激光反射率测量结果基本一致,说明该算法能够有效识别具有一定面积且材质均一的倾斜人工地物并计算修正其自身倾角对回波强度带来的影响,从而进一步提高基于回波强度值的地物可分性。 相似文献
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本文基于菲涅尔反射公式,结合现有的偏振反射模型对单叶与植被多角度偏振测量结果与理论结合进行分析;通过研究发现,偏振反射在前向散射方向可以通过菲涅尔反射公式进行解释,但是,在后向散射方向则需要考虑其他物理机理。此外,传感器获取的植被偏振信息既可以作为一种"噪声"来剔除,剔除后在可见光波段将相对误差从原来的30%降低到20%以内,又可以作为额外有效的信息源表征植被的结构特征:通过模型参数的大小判断冠层形态的平整程度。本文可以作为植被偏振探测的系统化方法,并且给出植被固有的偏振反射效应规律,即植被越平展光滑,产生的偏振信息越多;同时也将偏振光遥感在植被监测中的有效性凸显出来,即偏振信息的剥离有助于提升双向反射模型的计算精度。 相似文献
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地面三维激光扫描是获取对象表面几何信息的主要方法之一,扫描对象的完整性是三维激光扫描数据获取的基本要求。为解决实际扫描过程中,因作业空间受限等原因引起的扫描死角而导致点云缺失的问题,本文根据平面镜反射光线原理提出了针对非直视区域的普通平面镜辅助激光扫描数据的获取方法。分析了普通平面镜对激光光束传播路径与距离的影响机理,推导了激光扫描经普通平面镜反射像点对应的物点坐标解算方程;顾及激光扫描特性,设计了包含球标靶和普通平面镜的镜面反射系统,阐述了系统构建、系统检校与系统坐标系构建方法;并通过试验验证了本方法的可行性和精度。 相似文献
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Liangliang Tao Jing Li Xi Chen Qingkong Cai Yunfei Zhang 《Journal of the Indian Society of Remote Sensing》2017,45(4):621-629
This study investigated an appropriate method for soil moisture retrieval from radar images and coincident ground measurements acquired over bare soil and sparsely vegetated regions. The adopted approach based on a single scattering integral equation method (IEM) was developed to establish the relationship between backscatter coefficient and surface soil parameters including volumetric soil moisture content and surface roughness. The performance of IEM in 0–7.6 cm is better than that in 0–20 cm. Moreover, IEM can simulate correctly the backscatter coefficients only for the root mean square (RMS) height s < 1.5 cm at C-band and s < 2.5 cm at L-band by using an exponential correlation function and for s > 1.5 cm at C-band and s > 2.5 cm at L-band by using Gaussian function. However, due to the difficulties involved in the parameterization of soil surface roughness, the estimated accuracy is not satisfactory for the inversion of IEM. This paper used a combined roughness parameter and Fresnel reflection coefficient to develop an empirical model. Simulations were performed to support experimental results and to highlight soil moisture content and surface roughness effects in different polarizations. Results showed that a good agreement was found between the IEM simulations and the SAR measurements over a wide range of soil moisture and surface roughness characteristics. The model had a significant operational advantage in soil moisture retrieval. The correlation coefficients were 77.03 % at L-band and 81.45 % at C-band with the RMSEs of 0.515 and 0.4996 dB, respectively. Additionally, this work offered insight into the required application accuracy of soil moisture retrieval at a large area of arid regions. 相似文献
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Terrestrial brightness temperatures measured from satellites have been used to determine the surface emissivity. The results not only depend on surface temperature and on atmospheric properties, but also on the type of surface scattering. For otherwise identical conditions (same emissivity, same nonscattering atmosphere), the radiation above the Lambertian surface is larger than for a specular surface if the incidence angle is smaller than about 55/spl deg/. The opposite is true for larger angles. The effect leads to overestimates of emissivity for observations especially near nadir with the use of algorithms assuming specular reflection. The problem may be solved by the introduction of a specularity parameter to characterize realistic surfaces by a combination of specular and Lambert scattering. A simple solution lies in the use of conically scanning radiometers at a constant incidence angle near 55/spl deg/. Although the topic applies to all ranges of thermal radiation, the present discussion concentrates on the microwave spectrum in the Rayleigh-Jeans approximation. 相似文献
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An alternative approach to determine critical angle of contrast reversal and surface roughness of oil slicks under sunglint 总被引：1，自引：0，他引：1
Yansha Wen Mengqiu Wang Shaojie Sun Minwei Zhang Zhihua Mao 《International Journal of Digital Earth》2018,11(9):972-979
The critical angle is the angle at which the contrast of oil slicks reverse their contrasts against the surrounding oil-free seawater under sunglint. Accurate determination of the critical angle can help estimate surface roughness and refractive index of the oil slicks. Although it’s difficult to determine a certain critical angle, the potential critical angle range help to improve the estimation accuracy. In this study, the angle between the viewing direction and the direction of mirror reflection is used as an indicator for quantifying the critical angle and could be calculated from the solar/viewing geometry from observations of the Moderate Resolution Imaging Spectroradiometer (MODIS). The natural seep oil slicks in the Gulf of Mexico were first delineated using a customized segmentation approach to remove noise and apply a morphological filter. On the basis of the histograms of the brightness values of the delineated oil slicks, the potential range of the critical angle was determined, and then an optimal critical angle between oil slicks and seawater was then determined from statistical and regression analyses in this range. This critical angle corresponds to the best fitting between the modeled and observed surface roughness of seep oil slicks and seawater. 相似文献
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采用最小二乘方法解算超高阶重力场模型,不可避免会遇到大型矩阵的计算,直接求解是难以实现的。本文从重力场模型的基本观测方程出发,利用正余弦函数和面球谐因子的正交性,分析系数矩阵及法矩阵的特点,在法矩阵块对角化的基础上,利用系数矩阵求解法矩阵时“次m”递增的特点,对法矩阵求解方程进行约化、对Legendre函数的计算和存储方式进行了设计,结合缔合Legendre函数关于赤道的对称性,解决了大型矩阵存储及计算效率低下的难题,实现了超高阶重力场模型最小二乘方法的小存储、高效率的解算。通过试验模拟,改进后的方法相比传统块对角方法效率提高300倍,利用此方法可以在普通PC机上快速、高精度地解算2160阶次超高阶重力场模型,算法精度相比数值积分方法至少提高了5个数量级,并且在一定程度上可以评估原始观测数据的精度。 相似文献
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植被偏振特性研究对于植被监测与组分定量反演具有极其重要的作用。植被冠层的反射辐射具有偏振特性,这种特性与入射辐射和植被冠层结构相关。本文分析了偏振对光子—叶片—冠层之间细微相互作用及其变化的有效探测能力,并利用研究型扫描式偏振辐射仪RSP(Research Scanning Polarimeter)数据系统对比分析了偏振对不同叶倾角分布的估测。通过上述研究得出以下结论:(1)偏振观测能够对光线在冠层立体结构中的透射反射再出射过程给出精细刻画,若不用偏振手段对这一过程进行甄别并去除,则直接测算的植被散射系数会产生高达140%的误差;(2)利用偏振手段可以为高精度大倾角、多时相遥感观测提供可能,以此可改变目前光学遥感小角度、垂直观测的较严格约束;(3)偏振辐射呈现出随波长的稳定特性(相关系数0.96),使得利用偏振手段可以更好地研究冠层结构;(4)不同叶倾角分布对入射辐射存在不同的偏振反射,为利用多角度偏振信息进行遥感植被精细分类提供了新的途径。本文详细描述冠层结构和植被偏振特性的相互作用,通过对冠层立体结构与叶倾角的研究,刻画了植被定量遥感的方向性信息与高精度实现,为高分辨率遥感定量化的有效信息挖掘提供了新手段。 相似文献
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The information content of flood extent maps can be increased considerably by including information on the uncertainty of the flood area delineation. This additional information can be of benefit in flood forecasting and monitoring. Furthermore, flood probability maps can be converted to binary maps showing flooded and non-flooded areas by applying a threshold probability value pF = 0.5. In this study, a probabilistic change detection approach for flood mapping based on synthetic aperture radar (SAR) time series is proposed. For this purpose, conditional probability density functions (PDFs) for land and open water surfaces were estimated from ENVISAT ASAR Wide Swath (WS) time series containing >600 images using a reference mask of permanent water bodies. A pixel-wise harmonic model was used to account for seasonality in backscatter from land areas caused by soil moisture and vegetation dynamics. The approach was evaluated for a large-scale flood event along the River Severn, United Kingdom. The retrieved flood probability maps were compared to a reference flood mask derived from high-resolution aerial imagery by means of reliability diagrams. The obtained performance measures indicate both high reliability and confidence although there was a slight under-estimation of the flood extent, which may in part be attributed to topographically induced radar shadows along the edges of the floodplain. Furthermore, the results highlight the importance of local incidence angle for the separability between flooded and non-flooded areas as specular reflection properties of open water surfaces increase with a more oblique viewing geometry. 相似文献
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热红外遥感中大气下行辐射效应的一种近似计算与误差估计 总被引：12，自引：2，他引：10
在热红外遥感中,大气下行辐射效应很难处理,原因是地表双向反射分布函数很难精确描述。因此常见的处理方法是在如下２ 个假设前提下对该项作做简化计算： 一是假设地表反射为朗伯体特性,二是大气下行辐射在半球空间内取常数。该文提出了一种在地表为非朗伯体、大气下行辐射为非各向同性等一般条件下近似计算大气下行辐射效应的方法。通过数值模拟表明：（１） 所采用的方法可以在放弃２ 个假设的前提下,更精确地计算热红外大气下行辐射效应的数值,计算精度比２ 个假设前提下的计算方法至少提高２０ ．５３ ％ ;（２） 该方法所带来的误差是大气模式、遥感器视角和通道的函数。其中,通道４ 的相对误差比通道５大,同一通道中模式５ 的相对误差最大,但最大可能相对误差不到８ ％ ,且随扫描角的增大而减小;（３） 大气下行辐射效应项占总辐射亮度值之比例在±３０°视角范围内一般不超过４ ％ 。 相似文献
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双矩阵MD(Matrix-Doubling)算法是辐射传输方程的一种数值解,考虑了植被层内的多次散射信号,具有较高的模拟精度。但受限于算法的复杂性,很难直接应用到地表参数的反演中。本文以玉米覆盖地表为研究对象,基于MD算法的模拟数据,发展了一种L波段多角度微波辐射参数化模型。基于模拟数据的对比结果表明,参数化模型具有与理论模型相当的精度,两者之间的发射率误差不超过0.004(V极化)和0.007(H极化)。同时,结合黑河流域的地面实测数据,利用本论文中发展的参数化模型模拟了纯玉米像元的辐射亮温。该模拟结果与相同像元尺度上机载L波段微波辐射计(PLMR)观测亮温之间的差异基本在10 K以内。 相似文献
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双极化SAR数据反演裸露地表土壤水分 总被引：1，自引：0，他引：1
为了较高精度地获取大范围地表土壤水分,提出一种基于双极化合成孔径雷达数据的裸露地表土壤水分反演模型即非线性方程组,通过改进的粒子群算法求解非线性方程组从而得到土壤水分。首先通过AIEM模型数值模拟和回归分析,得到一种新的组合粗糙度,然后模拟分析得到土壤水分与雷达后向散射系数的关系,从而建立雷达后向散射系数与组合粗糙度、土壤水分的经验关系。利用ASAR C波段双极化雷达数据,基于经验关系和改进的粒子群算法即可实现土壤水分的反演。经过黑河流域实测土壤水分数据对模型进行验证,反演结果与实测数据具备良好的相关性(R~2=0.778 6)。与以往同一区域研究成果比较,文中的方法反演精度有所提高,更适用于裸露地表土壤水分反演。 相似文献
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利用激光强度信息分类激光扫描测高数据 总被引：21，自引：0，他引：21
三维机载激光扫描测高数据中不仅含有每个激光脚点的位置和高程信息，而且越来越多的系统同时能提供激光脚点回波信号的强度信息。不同反射面介质对激光信号的反射特性不一样．用实测的数据对激光回波信号的强度信息进行统计标定，并基于标定结果．实现了联合激光强度信息和高程信息进行分类的算法．获得了较为满意的结果。 相似文献
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本文分析了级数形式缓和曲线切线支距坐标公式与计算偏角的相互关系,当计算偏角大于90°应使用积分公式计算缓和曲线切线支距坐标,并推导了含任意非完整缓和曲线的路线交点曲线要素公式。 相似文献
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提出了Poisson重力边值问题,即关于扰动位的Poisson方程的Stokes问题和Neumann问题。作为导引,先研究Poisson方程的Dirichlet问题．再分别引入一种辅助函数,将Stokes问题和Neumann问题改化为Dirichlet问题,从而立即得到它们的积分解。最终解式表现为两部分叠加：一部分仅与边界观测相关,另一部分为对地形测量的响应,为研究地形测量对外部重力场和大地水准面的精化提供新的途径。 相似文献