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971.
Inventories of temperate forests of Central Europe mainly rely on terrestrial measurements. Rapid alterations of forests by disturbances and multilayer silvicultural systems increasingly challenge the use of conventional plot based inventories, particularly in protected areas. Airborne LiDAR offers an alternative or supplement to conventional inventories, but despite the possibility of obtaining such remote sensing data, its operational use for broader areas in Central Europe remains experimental. We evaluated two methods of forest inventory that use LiDAR data at the landscape level: the single tree segment-based method and an area-based method. We compared a set of structural forest attributes modeled by these methods with a conventional forest inventory of the highly heterogeneous forest of the Bavarian Forest National Park (Germany), which partially includes stands affected by severe natural disturbances. Area-based models were accurate for all structural attributes, with cross-validated average root mean squared error ranging from ∼3.4 to ∼13.4 in the best modeling case. The coefficients of variation for the mapped area-based estimations were mostly minor. The area-based estimations were varied but highly correlated (Pearson’s correlations between ∼ 0.56 and 0.85) with single tree segmentation estimations; undetected trees in the single tree segmentat-based method were the main sources of inconsistency. The single tree segment-based method was highly correlated (∼ 0.54 to 0.90) with data from ground-based forest inventories. The single tree-based algorithm delivered highly reliable estimates for a set of forest structural attributes that are of interest in forest inventories at the landscape scale. We recommend LiDAR forest inventories at the landscape scale in both heterogeneous commercial forests and large protected areas in the central European temperate sites. 相似文献
972.
一种改进的基于最小生成树的遥感影像多尺度分割方法 总被引:3,自引:1,他引:2
影像分割是遥感影像面向对象信息提取的基础步骤。基于多特征、多尺度及考虑空间关系的遥感图像分割是主流研究方向。本文基于eCognition软件的多尺度分割思想,引入基于图论的最优化理论,提出了基于最小生成树分割和最小异质性准则的多尺度分割方法。该方法采用相干增强各向异性扩散滤波和最小生成树分割得到初始分割结果,通过最小异质性合并准则同时考虑多波段光谱特性区域形状参数进行区域合并,实现多尺度的影像分割。本次研究选取两景试验影像,对本文方法和eCognition软件的多尺度分割方法开展了目视比较和定量指标评价,结果表明,本文提出的方法是一种有效的影像分割方法,在光谱差异较小区域的细分方面优于eCognition方法。 相似文献
973.
针对哈夫曼(Huffman)编码在遥感影像的压缩中鲜有研究这一情况,该文通过设计Huffman编码程序,对TM遥感影像单波段灰度图、分类图及以随机图作为对比进行了压缩测试,并对解码文件进行了直方图分析。结果表明,TM遥感影像7个波段在平滑缩放与非平滑缩放方式下的平均压缩效率为11.44%、36.72%;在5、10、15分类情况下的平均压缩效率分别为75.51%、63.60%和54.73%;随机图的直方图呈离散型均匀,压缩意义不大。因此,基于Huffman树的无损压缩编码可适用于遥感影像的压缩,具有一定的应用价值。 相似文献
974.
以若尔盖高原地区为研究区,利用多时相中分辨率成像光谱仪MODIS(Moderate Resolution Imaging Spectroradiometer)遥感影像数据,采用基于归一化植被指数(NDVI)的时间序列谐波分析方法,对2001~2013年夏季的MODIS/NDVI和MODIS/EVI进行重构,去除云干扰,采用决策树分类方法获取若尔盖高原地区2001~2013年夏季湿地信息的分布数据并作统计。结果表明:基于EOS/MODIS遥感数据,采用决策树分类方法获取若尔盖高原地区的湿地信息数据是可行的;若尔盖高原地区的湿地面积是随年际的变化呈锐减趋势,若尔盖高原地区湿地的退化主要是受到近年来气候暖干化的影响,人类活动则加剧了湿地萎缩及退化的趋势。 相似文献
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978.
The North Atlantic Oscillation (NAO) is the leading mode of atmospheric variability in the North Atlantic region, influencing storm tracks and creating a dipole pattern of precipitation from north to south across Western Europe. This distinct spatial distribution of precipitation provides a framework that can be potentially used to identify and reconstruct patterns of past NAO-forced climate variability. In this study we use tree-ring width series from Western Europe, in conjunction with principal components analysis and advanced spectral methods, to prospect for quasi-periodic climate signals that are forced by the NAO. We identify a robust 25-yr anti-phased synchronization in climate variability between Scandinavia and the Mediterranean during the 17th–20th centuries. The amplitude of the 25-yr beat displays a long-term modulation in northern and southern Europe, with minimum amplitude during the late Maunder Minimum. This amplitude minimum coincides with a maximum in Δ14C, suggesting a potential solar or oceanic influence on the intensity of the 25-yr band of quasi-periodic variability. 相似文献
979.
In regions of western North America with snow‐dominated hydrology, the presence of forested watersheds can significantly influence streamflow compared to areas with other vegetation cover types. Widespread tree death in these watersheds can thus dramatically alter many ecohydrologic processes including transpiration, canopy solar transmission and snow interception, subcanopy wind regimes, soil infiltration, forest energy storage and snow surface albedo. One of the more important causes of conifer tree death is bark beetle infestation, which in some instances will kill nearly all of the canopy trees within forest stands. Since 1996, an ongoing outbreak of bark beetles (Coleoptera: Scolytidae) has caused widespread mortality across more than 600,000 km2 of coniferous forests in western North America, including numerous Rocky Mountain headwaters catchments with high rates of lodgepole pine (Pinus contorta) mortality from mountain pin beetle (Dendroctonous ponderosae) infestations. Few empirical studies have documented the effects of MPB infestations on hydrologic processes, and little is known about the direction and magnitude of changes in water yield and timing of runoff due to insect‐induced tree death. Here, we review and synthesize existing research and provide new results quantifying the effects of beetle infestations on canopy structure, snow interception and transmission to create a conceptual model of the hydrologic effects of MPB‐induced lodgepole pine death during different stages of mortality. We identify the primary hydrologic processes operating in living forest stands, stands in multiple stages of death and long‐dead stands undergoing regeneration and estimate the direction of change in new water yield. This conceptual model is intended to identify avenues for future research efforts. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
980.
Rhys Whitley Daniel Taylor Catriona Macinnis‐Ng Melanie Zeppel Isa Yunusa Anthony O'Grady Ray Froend Belinda Medlyn Derek Eamus 《水文研究》2013,27(8):1133-1146
A modified Jarvis–Stewart model of canopy transpiration (Ec) was tested over five ecosystems differing in climate, soil type and species composition. The aims of this study were to investigate the model's applicability over multiple ecosystems; to determine whether the number of model parameters could be reduced by assuming that site‐specific responses of Ec to solar radiation, vapour pressure deficit and soil moisture content vary little between sites; and to examine convergence of behaviour of canopy water‐use across multiple sites. This was accomplished by the following: (i) calibrating the model for each site to determine a set of site‐specific (SS) parameters, and (ii) calibrating the model for all sites simultaneously to determine a set of combined sites (CS) parameters. The performance of both models was compared with measured Ec data and a statistical benchmark using an artificial neural network (ANN). Both the CS and SS models performed well, explaining hourly and daily variation in Ec. The SS model produced slightly better model statistics [R2 = 0.75–0.91; model efficiency (ME) = 0.53–0.81; root mean square error (RMSE) = 0.0015–0.0280 mm h‐1] than the CS model (R2 = 0.68–0.87; ME = 0.45–0.72; RMSE = 0.0023–0.0164 mm h‐1). Both were highly comparable with the ANN (R2 = 0.77–0.90; ME = 0.58–0.80; RMSE = 0.0007–0.0122 mm h‐1). These results indicate that the response of canopy water‐use to abiotic drivers displayed significant convergence across sites, but the absolute magnitude of Ec was site specific. Period totals estimated with the modified Jarvis–Stewart model provided close approximations of observed totals, demonstrating the effectiveness of this model as a tool aiding water resource management. Analysis of the measured diel patterns of water use revealed significant nocturnal transpiration (9–18% of total water use by the canopy), but no Jarvis–Stewart formulations are able to capture this because of the dependence of water‐use on solar radiation, which is zero at night. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献