地基激光雷达在森林参数反演中的应用

近年来地基激光雷达(TLS)得到了快速发展, 它能够快速地获取高精度、高密度的3D点云数据, 可以应用到工程设计、林业、农业、矿产、交通、城市规划和遗产记录等领域。在森林参数的定量测量应用上, 利用TLS测量森林参数如树高、胸径、密度和蓄积量等, 不仅节省人力, 还提高了工作效率, 现在已经成为一种快速获取树木几何参数的有效方法。文中主要介绍地基激光雷达遥感的工作原理、数据处理过程和方法、在林业中的应用现状、利用TLS数据反演森林参数(位置、胸径、树高、蓄积量、树干和郁闭度等)的方法和研究进展, 同时对地基激光雷达在林业中的应用前景进行了分析和展望。     

利用地基激光雷达估算不同地表条件下土方量

不同地表条件下土方量估算对土壤侵蚀量监测以及高标准农田工程建设具有重要意义,但基于地基激光雷达（Terrestrial Laser Scanning,TLS）的估算精度尚需求证。在江西省鹰潭市红壤生态实验站获取了7种不同地表条件下（植被覆盖度、砾石含量、地形起伏）填/挖土前后两期TLS数据,采用移动曲面拟合滤波与反距离加权插值方法计算填/挖土方量并验证,分析了TLS测站数量、位置与点云间距对计算精度的影响。结果表明：1）TLS在不同地表条件下估算土方量误差为1.69%～18.17%;2）在保证土方量计算精度的前提下,植被覆盖度小于1%、20%～30%的样方可分别将测站数量减少至2个和3个,低地势测站位置更有利于获取地表完整信息;3）TLS计算土方量的精度随点云间距增加而降低,近地表无覆盖、有覆盖的样方最优点间距分别为1～8和1～4 cm。研究为估算厘米级土体三维时空变化研究提供技术支持,为TLS野外观测设置提供依据。     

基于TLS数据的单木胸径和树高提取研究

利用TLS测量森林参数(树高、胸径和林分密度等)不仅节省人力,而且还能提高工作效率,目前已成为快速获取树木几何参数的有效方法之一。本文利用地基激光雷达数据,提出了一种半自动方式提取单木参数的方法。首先,利用发射脉冲与接收回波脉冲的形状偏差和强度对原始点云数据中的“飞点”和噪点进行滤除;然后,配准各站点云数据;接下来采用不同目标回波过滤方法滤除部分树叶点和其他非树干点;抽稀、合并各站点云数据,对合并后的点云数据水平分层并生成对应的灰度影像;对灰度影像采用Hough变换方法估测单木位置和胸径;对Hough变换检测层数较少的结果采用椭圆拟合方法重新检测;最后,结合Hough变换和椭圆拟合检测结果从点云数据中提取单木位置、胸径和树高。用小兴安岭凉水自然保护区的白桦天然次生林对算法进行了检验,5块多站扫描样地单木识别的平均精度为72.16%,将所提取的单木位置、胸径和树高与外业实际测量数据对比,结果一致性较高。5块多站扫描样地的胸径和树高均方根误差分别为2.38、2.55、3.58、2.21、1.92 cm和4.31、3.87、2.34、5.00、3.47 m。      

地基激光雷达技术在森林调查中的应用研究进展

森林资源的实时监测是森林经营管理的重要基础。地基激光雷达以其快速性、准确性、非破坏性和自动化等优点逐渐取代了传统的森林资源调查方法,可用于单木参数和林分信息的提取,特别是传统方法难以获取的冠层信息,并解决森林地上生物量估计中的不确定性。文中主要介绍地基激光雷达技术在森林资源调查中应用的研究现状,分析讨论该技术的优缺点,并对其未来的应用前景进行展望。     

Suitability of terrestrial laser scanning for studying surface roughness effects on concentrated flow erosion processes in rangelands

Surface roughness is thought to affect concentrated flow erosion – a major mechanism of soil loss on disturbed rangelands. However, quantifying surface roughness in the field at appropriately fine spatial scales is laborious and the scale at which to conduct meaningful roughness measurements is difficult to discern. Rapid, objective, and repeatable field methods are therefore needed to accurately measure surface roughness across a range of spatial scales to advance our understanding and modeling of concentrated flow erosion processes. Surface roughness can be derived from surface topography mapped at the sub-cm level using a field-portable terrestrial laser scanner (TLS). To test the suitability of terrestrial laser scanning for studying surface roughness effects on erosion processes in rangelands, we used concentrated flow simulation techniques at 8.5 m² plots that were randomly placed at rangeland sites in southeastern Oregon and southwestern Idaho, USA. Local surface roughness (locRMSH) was calculated as the standard deviation of TLS mapped surface heights within moving windows varying in size from 30 × 30 to 90 × 90 mm. The mean locRMSH of the eroded area and entire plot were negatively correlated (r² > 0.71, RMSE < 95.97 g min^− 1, and r² > 0.74, RMSE < 90.07 g min^− 1, respectively) with concentrated flow erosion. The strength of the locRMSH–erosion relationship and regression model parameters were affected by the moving window size, emphasizing the scale dependence of the locRMSH–erosion relationship. Adjusting locRMSH for slope effects decreased the strength of the locRMSH–erosion relationship from r² < 0.83 to < 0.26. Our results indicate that TLS is a useful tool to enhance our current understanding of the effect of surface roughness on overland flow erosion processes and advance hydrologic and erosion model parameter development. Further research is needed to evaluate the locRMSH – concentrated flow erosion relationship over a wider range of soil properties, surface conditions, and spatial extents.     

整体最小二乘法及其在坐标转换中的应用

本文举例表明了整体最小二乘法的优势,充分表明整体最小二乘法较之经典最小二乘法精度要高,结果更加准确。将整体最小二乘法引入坐标转换中,解决了以前坐标转换中许多未能解决的问题。并对于点位精度不同点的坐标转换,联合最小二乘法,提出一种迭代算法,减弱低精度点的影响。     

Radiotherapy-induced tumor lysis syndrome in a dog with thymoma

A 13-year-old, female, mixed-breed dog with a huge cranial mediastinal mass underwent radiotherapy (RT). On the following day, the dog presented with lethargy and anorexia. Hematological examination revealed elevated levels of blood urea nitrogen, creatinine, inorganic phosphorus, potassium, lactate dehydrogenase, creatine phosphokinase and aspartate aminotransferase, decreased calcium level, and metabolic acidosis. Urine output markedly decreased. The patient recovered with fluid therapy and diuretic therapy; however, died suddenly from an unknown cause 11 days after RT completion. Histopathological examination after necropsy showed thymoma in the cranial mediastinum and extensive tubular necrosis of both kidneys which may be due to RT-induced tumor lysis syndrome (TLS). This report suggests that the risk of TLS should be evaluated in dogs with thymoma who undergo RT.     

Structural response of black locust (Robinia pseudoacacia L.) and small-leaved lime (Tilia cordata Mill.) to varying urban environments analyzed by terrestrial laser scanning: Implications for ecological functions and services

Quantitative measurements of structure and morphology of urban trees are hardly exhausted so far, especially in regard to variations caused by altering urban environments. However, structure and functions of trees are heavily interwoven. In fact, knowledge about structural attributes is essential for a better understanding of urban ecosystem functions and services. In order to scrutinize spatially explicit and detailed structural attributes under varying urban environments, we acquired terrestrial laser scans and applied the according methodological approaches to the common urban tree species black locust (Robinia pseudoacacia L.) and small-leaved lime (Tilia cordata Mill.). We analyzed 52 small-leaved limes and 41 black locust trees within the city of Munich (Germany). Species as well as growing location had a significant effect on the height-diameter relation. We also found greater crown volumes for small-leaved lime. Black locust however, displayed more crown projection area and likely more shade efficient crown shapes at similar volumes. Stem inclination of black locust was found to be higher in parks than in street canyons with town squares lying in between. Furthermore, black locust displayed strong crown asymmetry in park areas, likely caused by competition with neighbors. The angles of main branches did not differ significantly between both species nor between the growing location. Branch angles, branch bending, the length of the branches as well as species and growing location had a significant effect on vertical crown center position, i.e. general crown shape. Surface complexity of lime is lower than of black locust, with its lowest manifestation in parks. Fractal-like crown surface structures, increasing surface roughness and complexity, were found to be more pronounced for black locust than for small-leaved lime. Thereby, black locust featured the highest crown surface complexity in parks, the lowest in street canyons. The results suggest that studies on spatially explicit tree structures may contribute to more target oriented tree plantings and thus, more effective exploitation of ecosystem services and benefits.     

基于优化PROSAIL叶倾角分布函数的玉米LAI反演方法

叶面积指数(LAI)是描述玉米冠层结构的重要参数之一,PROSAIL模型是常用于反演LAI的机理模型,能较为真实地反演植被冠层真实情况,但PROSAIL模型中使用的叶倾角分布函数假定区域内所有作物叶倾角分布是相同的,不能反映玉米植株真实的叶倾角分布情况。本研究以高分一号遥感影像和地基激光雷达点云数据作为数据源,充分利用地基激光雷达(TLS)在获取植被结构参数上的优势,通过体素化的方法对玉米叶片回波点云进行分割,获取每个拟合叶片单元的叶倾角,进而得到玉米植株真实的叶倾角分布,结合椭球分布函数得到玉米精确的叶倾角分布函数,实现对PROSAIL模型中叶倾角分布函数的优化。研究过程中分别基于未改进的PROSAIL模型和经过TLS优化后的PROSAIL模型反演黑龙江825农场主要玉米种植区的LAI。LAI反演结果表明:2种反演方法得到的LAI与实测LAI都具有较好的相关性,决定系数R2分别为0.557 6和0.858 3,模型可信度较高;但基于PROSAIL模型反演所得LAI结果偏低,在利用TLS数据提取叶倾角对模型进行优化后,反演LAI的估算精度由26.53%提高到96.23%。由此可知,通过引入TLS点云数据改进农作物叶倾角分布函数能大幅度提高LAI反演的准确性。     

Early season remote sensing of wheat nitrogen status using a green scanning laser

In-season, spatially variable nitrogen (N) fertilizer applications in agricultural systems can help to maximize crop N use efficiency and minimize N losses via hydrological leaching, runoff, and atmospheric volatilization. N fertilizer management often relies upon measurements of crop spectral reflectance using ground-based optical on-the-go sensors or hand-held chlorophyll meters. However, soil background reflectance can confound on-the-go sensing, especially during early crop growth stages, and hand-held chlorophyll meters are impractical for spatially explicit mapping at the field scale. Scanning laser technology is available that measures the intensity of the reflected laser light plus height information within a mm-scale ground instantaneous field of view at a very high sampling rate (up to 50,000 points s⁻¹ in this study). We examined the ability to quantify foliar N status of spring wheat (Triticum aestivum L.) using a green (532 nm) terrestrial laser scanner during an early stem extension growth stage (Zadoks growth stage 3.2). Laser data were processed by (1) removing soil background returns based on laser-determined height information, (2) standardizing green laser intensity based on white-reference panel readings, and (3) filtering noisy laser returns from leaf edges based on a laser return intensity threshold value. The return intensity of the reflected green laser light more accurately (r² = 0.68, RMSE = 0.30 μg g⁻¹) predicted foliar N concentration than conventional chlorophyll meter readings (r² = 0.36, RMSE = 0.41 μg g⁻¹) and spectral indices measured by a ground optical on-the-go sensor (r² < 0.41, RMSE > 0.39 μg g⁻¹). The results indicate that laser scanners are useful for measuring the N status of wheat during early growth stages, and provide justification for incorporating laser scanner based measurements into developing spatially-explicit estimates of foliar N during this critical growth period. Further research is needed to evaluate the operational practicality of a green scanning laser from a moving platform.