Evaluation of directional normalization methods for Landsat TM/ETM+ over primary Amazonian lowland forests     

《International Journal of Applied Earth Observation and Geoinformation》2017

Biodiversity mapping in extensive tropical forest areas poses a major challenge for the interpretation of Landsat images, because floristically clearly distinct forest types may show little difference in reflectance. In such cases, the effects of the bidirectional reflection distribution function (BRDF) can be sufficiently strong to cause erroneous image interpretation and classification. Since the opening of the Landsat archive in 2008, several BRDF normalization methods for Landsat have been developed. The simplest of these consist of an empirical view angle normalization, whereas more complex approaches apply the semi-empirical Ross–Li BRDF model and the MODIS MCD43-series of products to normalize directional Landsat reflectance to standard view and solar angles. Here we quantify the effect of surface anisotropy on Landsat TM/ETM+ images over old-growth Amazonian forests, and evaluate five angular normalization approaches. Even for the narrow swath of the Landsat sensors, we observed directional effects in all spectral bands. Those normalization methods that are based on removing the surface reflectance gradient as observed in each image were adequate to normalize TM/ETM+ imagery to nadir viewing, but were less suitable for multitemporal analysis when the solar vector varied strongly among images. Approaches based on the MODIS BRDF model parameters successfully reduced directional effects in the visible bands, but removed only half of the systematic errors in the infrared bands. The best results were obtained when the semi-empirical BRDF model was calibrated using pairs of Landsat observation. This method produces a single set of BRDF parameters, which can then be used to operationally normalize Landsat TM/ETM+ imagery over Amazonian forests to nadir viewing and a standard solar configuration.  相似文献   

机载WIDAS数据的Landsat卫星反照率初步验证   总被引：1，自引：1，他引：0  

何丹丹  焦子锑  董亚冬  张小宁  丁安心  尹思阳  崔磊  常雅轩 《遥感学报》2019,23(1):53-61

随着精细化监测的需求,中高空间分辨率的地表反照率产品逐渐成为气候模型的主要输入。目前,中高空间分辨率反照率产品的验证主要基于地表站点的通量塔观测数据,区域机载飞行数据的验证依然相对较少。因此,本文基于区域机载数据验证Landsat反照率产品。针对内蒙古自治区根河森林试验区所获取的机载红外广角双模式成像仪(WIDAS)多角度反射率数据,应用BRDF原型反演算法估算其反照率,分析了应用机载数据验证中高空间分辨率反照率产品的潜力。2016年内蒙古根河森林试验区机载WIDAS飞行多角度观测的可用多角度范围为25°,以前的研究表明BRDF原型反照率反演算法表现出对小观测角度的反照率反演结果的鲁棒性。因此,机载WIDAS反照率在一定程度可用于星载反照率的验证。首先,基于核驱动模型和各向异性平整指数(AFX)提取了试验区4种MODIS二向性反射分布函数(BRDF)原型;然后,将其作为先验知识应用到根河森林WIDAS机载数据的反照率反演中;最后,用WIDAS反照率和单个地面通量塔观测的反照率对Landsat卫星数据的反照率进行初步验证。验证结果表明Landsat反照率与WIDAS反照率结果较为一致,但略有低估,总体均方根误差(RMSE)约为0.02,偏差为0.0057。在多角度观测范围较小时,BRDF原型的反照率反演算法可为星载地表反照率的验证提供了一种有效的验证手段。  相似文献   

Effects of varying solar-view geometry and canopy structure on solar-induced chlorophyll fluorescence and PRI     

《International Journal of Applied Earth Observation and Geoinformation》2020

The increasing amount of continuous time series of solar-induced fluorescence (SIF) and vegetation indices (e.g. Photochemical Reflectance Index, PRI) acquired with high temporal (sub-minute) frequencies is foreseen to allow tracking of the structural and physiological changes of vegetation in a variety of ecosystems. Coupled with observations of CO₂, water, and energy fluxes from eddy covariance flux towers, these measurements can bring new insights into the remote monitoring of ecosystem functioning. However, continuously changing solar-view geometry imposes directional effects on diurnal cycles of the fluorescence radiance in the observation direction (F) and PRI, controlled by structural and biochemical vegetation properties. An improved understanding of these variations can potentially help to disentangle directional responses of vegetation from physiological ones in the continuous long-term optical measurements and, therefore, allow to deconvolve the physiological information relevant to ecosystem functioning. Moreover, this will also be useful for better interpreting and validating F and PRI satellite products (e.g., from the upcoming ESA FLEX mission).Many previous studies focused on the characterization of reflectance directionality, but only a handful of studies investigated directional effects on F and vegetation indices related to plant physiology. The aim of this study is to contribute to the understanding of red (F₆₈₇) and far-red (F₇₆₀) fluorescence and PRI anisotropy based on field spectroscopy data and simulations with the Soil-Canopy Observation of Photochemistry and Energy fluxes (SCOPE) model. We present an extensive dataset of multi-angular measurements of F and PRI collected at canopy level with a high-resolution instrument (FloX, JB Hyperspectral Devices UG, Germany) over different ecosystems: Mediterranean grassland, alfalfa, chickpea and rice.We found, that F₇₆₀ and F₆₈₇ directional responses of horizontally homogeneous canopies are characterized by higher values in the backscatter direction with a maximum in the hotspot and lower values in the forward scatter direction. The PRI exhibited similar response due to its sensitivity to sunlit-shaded canopy fractions.As confirmed by radiative transfer forward simulations, we show that in the field measurements leaf inclination distribution function controls the shape of F and PRI anisotropic response (bowl-like/dome-like shapes), while leaf area index and the ratio of leaf width to canopy height affect the magnitude and the width of the hotspot. Finally, we discuss the implications of off-nadir viewing geometry for continuous ground measurements. F observations under oblique viewing angles showed up to 67 % difference compared to nadir observations, therefore, we suggest maintaining nadir viewing geometry for continuous measurements of F and vegetation indices. Alternatively, a correction scheme should be developed and tested against multi-angular measurements to properly account for anisotropy of canopy F and PRI observations. The quantitative characterization of these effects in varying illumination geometries for different canopies that was performed in this study will also be useful for the validation of remote sensing F and PRI products at different spatial and temporal scales.  相似文献   

Atmospheric Corrections Using MODTRAN for TOA and Surface BRDF Characteristics from High Resolution Spectroradiometric/ Angular Measurements from a Helicopter Platform     

Yaping Zhou  Ken C. Rutledge Analytical Service & Material  Inc  Hampton  VA  USA Thomas P. Charlock Atmospheric Sciences Division  NASA Langley Research Center Hampton  VA  USA Norman G. Loeb  Seiji Kato Hampton University  Hampton  VA  USA 《大气科学进展》2001,(5)

l. IntroductionThe cIassicaI definition of bi--directional reflectance--distribution function (BRDF) is aderivative, distribution function, relatlng the irradiance incident from one given direction tolts contribution to the radiance renected in another direct1on (N1codemus et al., l977).f r (0,, rp,; 0,, rp, )= dL, (0,, P,; 0,, 9,; E, )/ dE, (0,, 9,) [sr-- 1 ], (l)where 0 (zenith angle) and 9 (azimuth angle) together indicate a direction, the subscr1pt i indi-cates quantities associated wi…  相似文献   

Ross-Li核驱动模型热点参数化及其校正—以POLDER数据为例   总被引：1，自引：1，他引：0  

常雅轩  焦子锑  董亚冬  张小宁  何丹丹  尹思阳  崔磊  丁安心 《遥感学报》2019,23(4):661-672

半经验、核驱动二向性反射分布函数(BRDF)模型是多角度遥感领域的一个重要模型,其热点效应在应用BRDF反演其它地表参数时有重要作用。本研究针对树冠内部叶片的间隙对热点的影响,对几何光学核的重叠函数进行热点效应的改进,并利用POLDER多角度观测数据集,对改进热点效应后的不同核函数组合模型的最优热点参数进行了确定。通过最小均方根误差(RMSE)筛选出最优热点参数,进一步分析不同模型对热点参数的敏感性和RMSE随热点参数的变化情况。结果表明:(1)该热点参数化方法可用于Ross-Li核驱动模型不同核函数组合的情况,热点校正后的模型相对于原模型很好地改善了对热点反射率的拟合能力;(2)热点参数最优值在几何光学核为LSRC (LiSparseRChen)与LDRC (LiDenseRChen)组成的模型中出现明显差别,C1在LDRC模型中的值远小于LSRC模型,主要是因为LDRC核函数自身较好考虑了树冠尺度下的热点效应,所以该热点参数改进方法起到的补偿作用较小;(3)总体上,同一模型的C1参数比C2参数对热点的变化更敏感。本研究为Ross-Li核驱动模型的热点效应进一步校正及热点参数的取值范围提供了依据,对Ross-Li模型的推广有重要意义,改进热点效应后的模型可用于未来国产多角度卫星的数据处理流程中,以获取加精确的地物热点反射率信息。  相似文献   

Evaluating the potential of multi-view data extraction from small Unmanned Aerial Systems (UASs) for object-based classification for Wetland land covers     

Tao Liu  Amr Abd-Elrahman  Bon Dewitt  Scot Smith  Jon Morton  Victor L. Wilhelm 《地理信息系统科学与遥感》2019,56(1):130-159

Unmanned Aerial Systems (UASs) have the potential to provide multi-view data, but the approaches used to extract the multi-view data from UAS and investigation of their use in image classification are currently unavailable in publications to our best knowledge. This study presents a method that combines collinearity equations and a two-phase optimization procedure to automatically project a point from real world coordinate system of an orthoimage to UAS image coordinate system (row and column numbers) to be used in multi-view data extraction. The results show average errors for the computed UAS column and row numbers were 1.6 and 1.8 pixels respectively evaluated with leave-one-out method. Based on this algorithm, it’s also for the first time that object-based multi-view data were extracted and presented, and the potential of using the multi-view data to aid Geographic Object-Based Image Analysis(GEOBIA) through bidirectional reflectance distribution function (BRDF) modelling was evaluated with two representatives of BRDFs, the Rahman-Pinty-Verstraete(RPV) and Ross-Thick-LiSparse (RTLS). Our results indicate the RPV model tends to overestimate the bidirectional reflectance for land cover types with high reflectance, while perform well for those with relatively low reflectance in our study area. To test the impact of using multi-view data on image classification, we extracted parameters from BRDF models and used these parameters as object features for object-based classification. The 10-fold cross validation results show that the 3-parameter RTLS significantly improved overall accuracy compared to the classifications relying only on the orthoimage features, while other BRDF models did not show significant improvements, raising the needs to develop new methods to better utilize the multi-view information in GEOIBA in the future.  相似文献   

AMTIS大气订正算法——基于MODTRAN4．1与BRDF大气订正环   总被引：1，自引：2，他引：1  

何立明  李小文  阎广建  王华  王锦地 《遥感学报》2004,8(5):389-396

基于BRDF大气订正环的途径和核驱动模型 ,用MODTRAN创建大气参数查找表 (LookUpTable LUT) ,加入地表先验知识 ,对AMTIS(AirborneMulti angleTIR/NIRImagingSystem AMTIS)的可见光、近红外波段数据进行了大气订正 ,并根据地面数据进行了验证。结果表明 ,采用本文算法比基于地表朗伯假定的大气订正能更有效地去除大气影响  相似文献   

用多角度遥感观测和BRDF模型对植物状况诊断评估(英文)     

Ｊ．Ｑｉ  Ｐ．Ｊ．Ｐｉｎｔｅｒ  Ｔ．Ｒ．Ｃｌａｒｋｅ  Ｂ．Ａ．Ｋｉｍｂａｌｌ  Ｍ．Ｓ．Ｍｏｒａｎ 《遥感学报》1997,(Z1)

用遥感技术进行植物评估可与光谱植被指数联系起来，如规一化差分植被指数ＮＤＶＩ。ＮＤＶＩ值的变化一般被认为是植被数量和密度的变化，但直接与植物生长状况有关的植物光谱特性也会导致光谱植被指数的变化。因此，低植被指数可能由于低密度或肥料不足二者之一或共同造成。这会限制植被指数作为监测手段的使用。二向反射分布函数ＢＲＤＦ模型把植物密度和光学特性区别对待，因而它有助于植物状况的客观评估。在这项研究中，我们测量了两个冬小麦冠层多角度光谱反射：一个氮肥充足，一个贫乏。这些测量随后用于ＢＲＤＦ的反演，来估计光学特性和植物密度。结果表明，同时获得这两种参数是可行的。因此，用ＢＲＤＦ和多角度遥感测量手段进行氮肥养料有关的植物状况诊断分析是可能的。结果也显示出这种方法中如反演和计算时间所带来的一些局限性。  相似文献   

单叶的反射特性(英文)     

《遥感学报》1997,(Z1)

  相似文献   

BRDF室内实验处理系统及应用(英文)     

高峰  朱启疆 《遥感学报》1997,(Z1)

与野外ＢＲＤＦ实验相比，室内实验更容易控制，具有无风、无云、光源固定和可全方位重复观测等优点，获取的反射率数据和测量的植被结构数据的精度要较野外测量的高，可用于ＢＲＤＦ模型验证及反演试验。  相似文献