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1.
植被覆盖度是反映地表植物群落覆盖程度的一个重要参数,无论是用照相法还是用卫星遥感图像提取,都是通过依次计算每个像元来获取整张图像的覆盖度,这种方式在处理大尺度遥感图像或者像元数量较多的遥感图像时,会耗费较多的时间。为此,提出一种利用抽样法估算遥感图像植被覆盖度的新方法,即在每张图像中随机选取一定数量的像元,计算所选像元的植被覆盖度来表示整张影像的植被覆盖度,利用误差概率模型进行精度控制,使结果误差在合理范围内。通过控制图像数和抽样像元数验证了该方法的精度。对于照相法而言,当采样数超过384个时,误差基本稳定在0.005以内,相比逐像元法计算的误差可以忽略;对于遥感影像二分法,当处理的遥感影像为100张、采样点数为300个时,均方根误差基本稳定在0.02以内,同时耗时仅为逐像元法的1%以下。试验表明,利用抽样法估算影像植被覆盖度可以在满足精度的条件下,大大降低计算时间,提高工作效率。 相似文献
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植被覆盖度的照相测量及其自动计算 总被引：6，自引：3，他引：3
植被覆盖度是描述陆地表面植被特征的一个重要参数.快速准确的测量植被覆盖度,对研究植被覆盖与土壤侵蚀关系,植被覆盖的水土保持效益,以及土壤侵蚀预报等具有重要意义.在多年实践的基础上研制出的便携型植被覆盖度摄影仪,适用于野外平地或山坡的植被覆盖度的照相测量,能方便地调节相机距地表面高度和增强相机的拍摄稳定性.同时开发了便携型植被覆盖度摄影仪的配套软件--植被覆盖度自动计算系统(PCOVER),能对获取的植被图像进行自动判读并估算植被覆盖度,实际应用显示有很好的判读精度. 相似文献
3.
地表砾石是各种水文和侵蚀等过程综合作用的产物,是土壤退化和生态系统恶化的一个标志;反过来这些砾石也影响到侵蚀的各个过程。分别利用视点框架法和照相法对不同粒径样本下(2~6mm,6~20mm,20~60mm)的砾石覆盖度进行了测量,对比分析了不同砾石覆盖度测量方法对其精度的影响。结果表明,采用两种测量方法观测砾石覆盖度均能达到一定精度,视点框架法测量的砾石覆盖度相对误差变化范围为-7.84%~80.86%,平均相对误差为15.69%,照相法测量的砾石覆盖度相对误差变化范围为-48.35%~9.89%,平均相对误差为-11.69%。随着砾石覆盖度的增加,视点框架法测量的相对误差绝对值表现为减小。视点框架法测量的最大相对误差均值的绝对值随着抽样次数的增加而减少,当抽样次数达到约30,相对误差减小的趋势减缓。 相似文献
4.
照相法结合数字图像技术计算植被覆盖度精度研究 总被引：9，自引：1，他引：9
植被覆盖是影响土壤侵蚀的一个重要因子,植被覆盖度的测量精度直接影响到土壤侵蚀模型参数的滤定或侵蚀量的估算。用0.1 m×0.1 m的绿色硬纸块铺设在面积已知的水平小区和坡度小区上模拟植被覆盖,用自行设计的照相装置对铺有模型的小区进行垂直照相。用GIS软件IDRISI分类计算和Pho-toshop软件环境下目视解译提取照片植被覆盖度。试验结果表明,这2种方法计算得出的覆盖度与实际覆盖度相差不大,分类计算得出覆盖度的绝对误差在0.6%~4.3%之间;从绝对误差的最小值、最大值、均值和方差来看,目视解译值比分类计算值更接近于实际覆盖度,但考虑到工作量和植被覆盖度计算精度的要求,选择GIS软件IDRISI来进行照片植被覆盖信息的提取是可行的。 相似文献
5.
为提高长时间序列叶面积指数测定模型的模拟精度,该文设计一种可以长期在野外间接测量叶面积指数仪器,仪器由太阳能提供持久电能,利用单片机控制垂直水平舵机,带动光强传感器记录多角度光线强度,在2台仪器同时测量的情况下,获得光线透过林分冠层多角度光强衰减率,通过编写计算程序解算林分叶面积指数。使用商品化光学仪器LAI-2200验证该仪器测量精度,对24块样地叶面积指数进行测量,两仪器测量结果高度吻合R2为0.927,绝对标准误差为0.36。长时间野外叶面积指数自动测量获取数据可节省人力、减少人为误差。 相似文献
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3种地表随机糙率测量方法比较 总被引：1，自引：0，他引：1
《水土保持研究》2020,(4)
为定量比较3种地表随机糙率测量方法的异同,采用砾石覆盖、枯落物覆盖及不同农事活动3种下垫面条件,分别利用三维激光扫描法、照相法和测针法测量了不同处理下的地表随机糙率,以激光扫描法测量结果为基准值,通过绝对误差、相对误差和均方根误差比较了3种测量方法的差异。结果表明:激光扫描法测量精度最高,但仪器价格昂贵,且用于野外测量时需要注意光照影响;照相法精度较高,测量快捷方便,与扫描法的平均绝对误差为0.65 mm,平均相对误差为14.0%,但需手动测量各控制点间的相对距离,也需要避免光照影响;测针法易于操作、成本最低,但费时费力、精度不高,与扫描法的平均绝对误差为1.82 mm,平均相对误差为34.1%。因此,3种方法各有利弊,需根据实际情况选择合适的测量方法测定地表随机糙率,当精度要求不是非常严格时,推荐优先使用照相法。研究结果对随机糙率测量方法的正确选择,提高地表糙率测量精度,具有重要的指导意义。 相似文献
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8.
冬小麦叶面积指数地面测量方法的比较 总被引：12，自引：8，他引：4
该研究以冬小麦为对象,对叶面积指数测量的几种方法（比叶重法、照相法及SUNSCAN测量法）从测量难易程度、误差来源、适宜条件等方面做了比较分析与评价。研究表明比叶重法及照相法在整个生育期间均可使用,而基于SUNSCAN的仪器测量法在冬小麦封垄前的测量还需进一步研究。对SUNSCAN一天内不同时间测量的结果进行了比较,得出最适宜测量时间为13:00－15:00。照相法的测量精度最高,比叶重法次之,SUNSCAN测量需要根据作物生长特点做参数修正。针对SUNSCAN测量LAI提出了一种对叶倾角分布参数进行修正的方法,对3种冬小麦株型品种3个不同生育期进行了参数修正。该研究有助于地面测量叶面积指数的方法选择,同时对提高SUNSCAN测量精度具有参考意义。 相似文献
9.
夏玉米冠层光合有效辐射垂直分布模型 总被引：5，自引：4，他引：1
吸收光合有效辐射分量（FPAR）是研究植被群体光合作用和光能利用的重要参数,弄清冠层内FPAR的垂直分布规律及其与冠层结构等参数之间的定量关系,可以为遥感定量反演冠层FPAR提供模型基础。该文基于平均冠层的辐射传输过程,结合冠层结构建立玉米冠层内FPAR垂直分布计算模型,并就模型的参数如植被组分光学特性、株型、太阳高度角以及天空散射光比例等对FPAR垂直分布结果的影响进行了分析。利用实测结构参数模拟了玉米冠层内FPAR,并与SUNSCAN测量值进行了比较,结果表明模型对封垄后的玉米冠层内FPAR垂直分布的模拟精度较高,RMSE均小于0.18,并能较好地计算封垄前冠层内FPAR的垂直分布趋势。 相似文献
10.
基于器官尺度虚拟玉米冠层直射光分布的快速计算模型 总被引：2，自引：0，他引：2
为了给精确农业研究中所需的植物冠层光分布快速计算提供解决方法，提出了一个基于虚拟相机的玉米冠层直射辐射分布快速计算模型。该模型主要包括一个能代表田间玉米植株群体空间结构特征的虚拟冠层和一个虚拟相机，采用虚拟相机从太阳入射方向拍摄冠层图像，通过图像判读计算出植株各器官的太阳直射辐射分布。从模拟精度与模拟时间两方面评估了该模型的有效性。结果表明，该模型能很好地模拟器官尺度的植株光分布，并且比现有模型明显地缩短了计算时间。在引入计算虚拟冠层最小复制植株数的算法后，该模型的计算时间还能进一步缩短。另外，还探讨了虚拟冠层的植株器官形态简化描述的可行性，结果表明过度简化会导致模拟误差的明显增加。 相似文献
11.
Craig Macfarlane 《Agricultural and Forest Meteorology》2011,151(7):833-840
A great drawback of photographic methods for estimating canopy metrics such as leaf area index (L) and cover has been the tedious and time consuming image processing step and the perceived sensitivity of the results to image processing. This paper describes an automatic method, the ‘two-corner method’, for detecting homogeneous regions of canopy and sky, and for quantifying the number of mixed pixels in canopy images. Mixed pixels are pixels of intermediate brightness value that do not very obviously belong to either sky or canopy. Four image classification methods were tested for classifying mixed pixels as canopy or sky. When applied to both fisheye and cover images of Eucalyptus forest, none of the more complicated classification methods yielded results that greatly differed from a simple global binary threshold classification, even if those metrics were derived from the zenithal distribution of gap fraction or gap size. Increasing photographic exposure by one stop reduced calculated L by 9-12%, but modern digital camera technology makes it much easier to correctly expose fisheye canopy images, either by examining the image histogram in the field or by taking multiple exposures and choosing the best exposures after automatic processing. This study is the first to systematically quantify the number of mixed pixels in canopy images and demonstrated that fisheye images contain more mixed pixels than cover images, and that the number of mixed pixels increases with increasing vegetation cover. In conclusion, the recent advances in digital camera technology, combined with robust and automated image analysis methods, are rapidly bringing the field of photographic analysis of canopy structure to maturity, where the field techniques and image processing aspects of the methodology are no longer significant factors limiting its application by non-experts. In the case of fisheye photography, research is still needed to improve the estimation of L in clumped canopies. 相似文献
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《Agricultural and Forest Meteorology》2004,121(1-2):19-35
Rapid, reliable and objective estimations of leaf area index (LAI) are essential for numerous studies of atmosphere–vegetation interaction, as LAI is very often a critical parameter in process-based models of vegetation canopy response to global environmental change. This paper reviews current knowledge concerning the use of direct and indirect methods for LAI determination. The value of optical LAI measurements by means of hemispherical photography has already been demonstrated in previous studies. As clumping seems to be the main factor causing errors in indirect LAI estimation, we suggest that the use of a digital camera with high dynamic range has the potential to overcome a number of described technical problems related to indirect LAI estimation. Further testing and defining of a standardised field protocol for digital hemispherical photography is however needed to improve this technique to achieve the standards of an ideal device. 相似文献
14.
无人机飞行高度对植被覆盖度和植被指数估算结果的影响 总被引：1，自引：1，他引：0
将无人机与多种成像传感设备相结合可实现田间作物表型信息的全面获取。针对田间复杂环境下无人机搭载多种成像传感设备在不同飞行高度处提取的作物信息具有差异性的问题,本研究着重探究了无人机搭载两种成像传感设备获取图像时,不同飞行高度对估算植被覆盖度以及植被指数结果的影响。首先为防止外界环境变化对获取图像质量造成干扰,通过最近邻插值算法将无人机飞行高度为25 m处获取的两个多光谱和可见光图像数据集分别退化为十个不同地面分辨率的模糊图像数据集,以模拟无人机在不同飞行高度中获取的作物图像。然后获取50m高度处的无人机图像数据集通过皮尔逊相关性分析验证模拟数据集的有效性。最后采用随机森林模型估算不同数据集中的植被覆盖度,分类精度大于91%。结果发现,当植被覆盖度小于二分之一时,随着地面分辨率的降低该指标不断被低估,反之则被高估。飞行高度50 m的真实图像与模拟图像估算植被覆盖度结果的相关系数r为0.992 8,两者具有强相关性,模拟图像估算得到的植被覆盖度变化具备参考意义。植被指数估算结果中,首先对无人机图像数据集进行辐射校正、阈值分割等图像预处理,然后根据公式计算得到植被指数,最后通过假设性检验对十个图像数据集计算得出的植被指数进行分析。结果发现,可见光植被指数在飞行高度61 m时具备显著性差异,多光谱植被指数在十个高度下均没有显著性差异,因此为保证无人机获取数据的准确性与完整性,建议当无人机搭载本文的两种相机获取作物信息时建议飞行高度不高于61 m。本研究为研究者利用无人机搭载多传感设备获取作物信息设定合适的飞行高度、减小作业成本提供参考。 相似文献
15.
Judith L. Fisher William A. Loneragan Kingsley Dixon Julie Delaney Erik J. Veneklaas 《Biological conservation》2009,142(10):2270-2281
Relationships between fire history, vegetation structure and composition, and invasion by introduced plant species have received limited attention in Australian woodlands. A study in a Mediterranean, fire adapted urban Banksia woodland remnant in the biodiversity hotspot of southwest Australia investigated: (1) Have significant changes occurred in the woodland tree canopy between 1963 and 2000? (2) Do correlations exist between fire frequency and canopy cover? (3) If there is a difference in the vegetation composition of Banksia woodland invaded by the South African Ehrharta calycina (PCe) and Pelargonium capitatum (PCp) compared to largely intact remnants (GC)? and (4) Do correlations exist between vegetation condition, composition, fire frequency and invasion? Aerial photography, processed in a Geographical Information System, was used to establish fire history and changes in canopy cover over time (1963–2000). PCe and PCp sites experienced the greatest number of fires, with a net reduction in canopy cover in all areas experiencing four or more fires (60% of all woodlands). Frequent fire corresponded with a decline in native cover, richness and diversity, a shift from native to introduced species, changes in the relative importance of fire response categories, and loss of native resprouting shrub cover. Life forms of introduced species, which included no trees, shrubs and perennial sedges, contrasted strongly with those of native species, which had poor representation of annual and perennial grasses. Clear ecological and conservation consequences due to the loss of species diversity, changes in fire ecology and invasion have occurred in the Banksia woodlands. This study provides an understanding of the invasion process, enhancing conservation knowledge to improve the adaptive management of the key threatening process of invasion in biodiverse communities. 相似文献
16.
基于数码相机的水稻冠层图像分割及氮素营养诊断 总被引：11，自引：3，他引：8
利用数码相机对作物进行快速准确的营养诊断,需要对图像中作物冠层部分与非冠层部分进行有效的分割。该文依据绿色植被和土壤在可见光区域反射光谱的差异,提出了根据数字图像绿色通道和红色通道差值的大小设定阈值对图像进行分割的方法。阈值设定为10～20之间时对水稻冠层图像有较好的分割效果,拔节期和孕穗期获得最佳图像分割效果的阈值分别为10与20。分割后图像中提取的特征参数与SPAD值、叶片含氮量等指标间具有良好的相关关系,其中红光标准化值NRI与两者间的相关系数达到-0.87和-0.65。该方法能准确地分割水稻冠层图像,且简便易行,对绿色植被的图像分割具有普适性,有较高应用价值。 相似文献
17.
The effect of land cover/vegetation on soil water dynamic in the hilly area of the loess plateau,China 总被引：1，自引：0，他引：1
Severe soil and water loss has lead to widespread land degradation in China's loess plateau. During the past decades, a great deal of effort was made on vegetation restoration to reduce soil and water loss in the loess plateau. However, due to water shortage the efficiency of vegetation restoration was not as satisfactory as expected. As part of a vegetation restoration project, we conducted research aiming to understand the relationship between vegetation pattern and soil water dynamics. The goal was to find vegetation types appropriate for the loess plateau with scarce water resources. In 1986, fifteen plots of land were planted with five vegetation types: pine woodland, shrubland, sloping cropland, alfalfa and semi-natural grassland. Soil water content, runoff, soil erosion were measured for each plot. Environmental variables, such as rainfall, evaporation and temperature, were recorded simultaneously by an automated meteorological station. The relationship between land cover pattern and soil water dynamic was evaluated by using statistical models. We found that: (1) soil water loss occurred during the growing season, and it reached the maximum in the second half of July; (2) soil water was not fully replenished from rainfall during the rainy season; (3) pine woodland induced the largest water loss to surface runoff, followed by sloping cropland, alfalfa, semi-natural grassland and shrubland; the poor capability of pine woodland for water conservation may be attributed to soil compaction and poor ground coverage under the tree; (4) in most cases, soil water of the five vegetation types was low except for shrubland and semi-natural grassland where it was moderate-high during a few periods. These conditions inhibit sustainable vegetation growth in the semi-arid loess hilly area of the loess plateau, China. 相似文献
18.
土壤干化的水文生态效应 总被引：1，自引：0，他引：1
应用土壤-植被-大气传输模型(SVAT-model)——CoupModel,对黄土丘陵沟壑区农地(马铃薯)、林地(刺槐林)、采伐迹地(刺槐被砍伐)和荒草地(天然灌草)的土壤水分变化进行了模拟。分析了不同植被覆盖条件下土壤干化程度、气候干旱和植被耗水对土壤干化的贡献率以及土壤干化的水文生态效应。研究结果表明:农地不存在土壤干化现象,刺槐林地、采伐迹地和荒草地均存在明显的土壤干层,以刺槐林地最为严重;气候干旱和植被过度耗水对土壤干化的贡献率分别为70.74%和29.26%,气候干旱是导致土壤干化的主要原因;土壤干化可以导致土壤剖面水分交换深度变浅,土壤剖面水分的移动性变差,使土壤水库丧失77.58%~93.55%的调节能力,形成土壤水分循环的隔离层,增加植被生长对年度降水的依赖性。总之,土壤干化恶化了陆地土壤水文循环环境,影响植被的正常生长,不利于黄土丘陵沟壑区的生态环境建设。 相似文献
19.
Mirco Migliavacca Marta Galvagno Edoardo CremoneseMicol Rossini Michele Meroni Oliver SonnentagSergio Cogliati Giovanni MancaFabrizio Diotri Lorenzo BusettoAlessandro Cescatti Roberto ColomboFrancesco Fava Umberto Morra di CellaEmiliano Pari Consolata SiniscalcoAndrew D. Richardson 《Agricultural and Forest Meteorology》2011,151(10):1325-1337
The continuous and automated monitoring of canopy phenology is of increasing scientific interest for the multiple implications of vegetation dynamics on ecosystem carbon and energy fluxes. For this purpose we evaluated the applicability of digital camera imagery for monitoring and modeling phenology and physiology of a subalpine grassland over the 2009 and 2010 growing seasons.We tested the relationships between color indices (i.e. the algebraic combinations of RGB brightness levels) tracking canopy greenness extracted from repeated digital images against field measurements of green and total biomass, leaf area index (LAI), greenness visual estimation, vegetation indices computed from continuous spectroradiometric measurements and CO2 fluxes observed with the eddy covariance technique. A strong relationship was found between canopy greenness and (i) structural parameters (i.e., LAI) and (ii) canopy photosynthesis (i.e. Gross Primary Production; GPP). Color indices were also well correlated with vegetation indices typically used for monitoring landscape phenology from satellite, suggesting that digital repeat photography provides high-quality ground data for evaluation of satellite phenology products.We demonstrate that by using canopy greenness we can refine phenological models (Growing Season Index, GSI) by describing canopy development and considering the role of ecological factors (e.g., snow, temperature and photoperiod) controlling grassland phenology. Moreover, we show that canopy greenness combined with radiation use efficiency (RUE) obtained from spectral indices related to photochemistry (i.e., scaled Photochemical Reflectance Index) or meteorology (i.e., MOD17 RUE) can be used to predict daily GPP.Building on previous work that has demonstrated that seasonal variation in the structure and function of plant canopies can be quantified using digital camera imagery, we have highlighted the potential use of these data for the development and parameterization of phenological and RUE models, and thus point toward an extension of the proposed methodologies to the dataset collected within PhenoCam Network. 相似文献
20.
改性纤维素类聚合物固沙剂的吸附力学及崩解特性试验 总被引：3，自引：1，他引：2
山地植被信息在气候变化研究和生态环境保护等方面发挥着重要作用,遥感技术能够快速获取山地植被信息,但是存在山地地形阴影的影响以及山地植被信息混淆问题。该文以山地植被为研究对象,基于Landsat卫星遥感影像多光谱数据,分析山地植被的主要特点,借鉴阴影消除植被指数（SEVI）的构造原理及形式,提出了一种适用于山地植被覆盖遥感监测的植被指数算法--植被区分阴影消除植被指数（VDSEVI）。研究结果表明：相对于已有的其他植被指数,VDSEVI较好地消除了地形阴影的影响;VDSEVI的信息量大,植被覆盖的识别能力较强,较好地解决了植被信息混淆问题,能够更好地反映山地植被覆盖情况。不同土地覆盖类型的VDSEVI存在显著差异;阴影稀疏林地和相邻非阴影稀疏林地的相对误差较小,为3.428%;各土地覆盖类型样本VDSEVI标准差均小于0.06;植被覆盖样本VDSEVI与太阳入射角的余弦值（cosi）的相关系数为?0.800。为验证VDSEVI在其他地区的适用性,将VDSEVI应用于内蒙古阿尔山和福州市闽侯县,结果表明VDSEVI同样适用。新疆那拉提、内蒙古阿尔山和福州市闽侯县3个区域基于VDSEVI阈值法的植被信息提取总体精度分别为84.136%、87.339%、86.709%,Kappa系数分别为0.799、0.788、0.791。 相似文献