小型无人机林火监测与图像处理技术

常规传感式火灾监测方法不能满足现代林火监测灵活性、实时性和高效性的要求。针对森林这种复杂大空间场景,提出一种基于无人机平台和动态特征分析的视频图像型火灾检测算法。通过机载摄像机拍摄森林视频图像,建立基于混合高斯背景模型和颜色模型多级火灾隐患特征验证算法。实验结果表明,本文方法能较快识别火灾隐患,降低误检率,可为相关研究和实际应用提供参考。     

基于鲸鱼算法的森林火灾图像多阈值分割

为监测森林火灾的实时火情,本文研究图像分割算法应用于林火图像的识别。由于林火图像背景复杂干扰目标多,采用单阈值Otsu方法对林火图像进行分割的精度较差,因此本文研究鲸鱼优化算法(Whale Optimization Algorithm,WOA)对多阈值图像分割的最佳阈值进行寻优。鲸鱼优化算法是在寻找最优解的过程中效率较高的算法,该算法具有收敛速度快、精度高的特点。针对森林火灾图像中的火焰区域准确分割问题,应用WOA对Otsu的适应度函数进行寻优,在红绿蓝模式的林火数字图像上进行仿真试验。试验结果表明:提出的算法在森林火灾图像多阈值分割中优于传统单阈值的Otsu算法,可以获得更为准确的分割阈值和更高的分割效率,具有较强的工程实用性。     

小型无人机在森林防火中的应用探讨

在预防和扑救森林火灾的过程中，及时、有效、连续地掌握林火发生、蔓延发展第一手火情信息极为重要。近年来，小型无人机技术不断完善，开发应用成本逐渐降低，利用小型无人机搭载不同的任务设备，执行火情侦察和火场监测任务，及时发现林火、提供火点位置以及实时获取林火发展蔓延态势等准确的林火信息，已成为森林防火研究领域的热点内容之一。无人机通过搭载不同的任务载荷可以逐步分担起已往有人机承担的林区巡护、卫星热点侦察、火场勘察等监测工作，使有人机尽可能应用到对林火的直接扑救中，开发利用适合于森林防火应用的高性能无人机及搭载平台能弥补我国森林航空消防有人机的许多不足，仍是现阶段森林防火工作中重要的研究领域。     

森林火灾火焰像素检测的背景减除算法

背景减除(background subtraction,BS)是森林火灾火焰图像中运动像素检测的主要手段,已有文献多采用高斯混合模型进行运动像素检测,然而GMM算法对于背景包含大量运动像素的视频并不能取得好的效果,而野外环境的森林火灾视频风吹树枝叶会导致大量的运动像素。为更好地提取森林火焰的运动像素,对36种BS检测算法应用于光照强度变化、树枝叶摆动、相机抖动等多种森林火灾视频进行实验,并选择4种效果好的BS检测算法(高斯平均值背景减除法(DPWren GA)、改进的高斯混合模型(DPZivkovic AGMM)、混合高斯背景模型(Mixture Of Gaussian V2)、局部二进制相似度分割背景减除法(LOBSTER))进行分析研究。结果表明,DPWren GA法检测到的前景完整性不够理想,但其噪声点最少,精确率最高。LOBSTER法能最完整地分割出前景。4种算法对阳光强烈的场景和存在树枝遮挡的火灾视频的检测效果都不是很理想,但对相机抖动有较好的适应性。     

基于时空特征的林火视频火焰识别研究

由于森林火灾监控现场是野外广阔的林区,而且树叶的摇摆使得视频图像中的运动对象很多,强烈的阳光、秋季的枯叶和红枫会导致火灾识别的误报等,这些特点都使得现有室内或静止场景火灾视频监控的视频处理技术不再适用。考虑到火灾发生有一个蔓延的过程,是一个包含若干连续视频帧图像的视频片段,笔者首先将疑似火焰视频划分成时空视频块,根据颜色特征和运动特征得到疑似火焰区域,然后在视频片段大粒度下基于空间静态特征(纹理、圆形度特征)和时序动态特征(火焰面积变化、形状相似性、闪烁频率特征)提取火焰特征向量,最后使用基于Ada Boost的算法进行火焰识别,实现森林火灾的实时检测。结果表明,该方法能够准确有效地进行林火视频火焰识别。     

小型无人机非测量相机在林业调查中的应用研究

为提升林业调查的技术水平,研究小型无人机搭载非测量相机在林业调查中的应用技术。选择北京十三陵林场开展低空航拍试验,针对非测量相机的镜头畸变和小型无人机相机云台外方位元素误差较大的特点,分别通过相机检校算法和外方位元素逆向求解,进行内外方位元素定向,生成立体像对和正射影像;用地面控制点对相片整体进行几何精校正,采用3D量测工具测量立体区域树高,用地面控制点测量图像拼接区域面积和周长,用现地实测树高、面积和周长对图测结果进行检验和模型拟合。结果表明,通过适当的校正和调整,小型无人机搭载非测量相机基本能够满足林业调查对树高、面积及周长等的量测精度要求,应用前景广阔。     

无人机在林火防控中的应用

介绍无人机技术应用于林火防控的发展历程和典型案例。目前,无人机在林火防控中,主要用于火情侦察、灾后勘察和灾情评估,尚未形成与现有林火防控措施的有效协同机制。其原因除了无人机本身的技术局限性,还在于传统的林火防控预案中,未能纳入无人机协同作战的方案,无人机仅起到了信息辅助的作用。未来的林火防控中,应进一步提高火灾环境信息监测能力;与此同时,在无人机与消防员协同作战以及无人机与载人直升机协同作战等方面不断积累经验,形成完整预案,最大限度减少人员伤亡,提高林火防控效率。     

林火视频监控中烟识别方法的探讨

森林火灾是一种世界性的重要自然灾害,具有传播速度快、灭火和营救都比较闲难等特点,利用视频图像的林火探测技术不受室外空间和恶劣环境的影响,适合于森林火灾的监测报警,是一种新型有效的火灾探测技术.本文通过对火灾现场视频图像中烟图像特征、烟纹理特征、烟动态特征、烟形状特征的分析,分析了火灾烟图像特征,从而排除干扰现象而识别出火灾烟.     

基于改进C4.5算法的森林火险天气等级评估

应用数据挖掘技术,对影响林火的因子进行数据分析与综合评估。针对林火这一课题的特殊性与复杂性,采用一种改进的C4.5决策树算法对森林火险天气等级进行评估决策。该算法着眼于从一组互不相关的事例中推算出以决策树为表现形式分类规则,并采用基于可信度阈值的后剪枝技术降低决策树纯度。基于算法原理,综合分析了温度、湿度、风力等林火因子数据集,分析了决策树算法应用于数据分类和知识发现的过程和特点,研究了该决策树模型在天气评估中的应用,建立了一套森林火险天气等级评估方法。通过试验表明,林火等级与各林火因子数据集之间建立了有机联系,实现了该算法在林火等级评估方面应用的可能,同时,也指出了该算法应用的局限性与待解决的问题。     

林火自动识别报警系统研建

运用图像识别、模式识别和地理信息系统(GIS)技术进行林火自动识别报警,通过对摄像头摄取的图像进行处理,提取其颜色特征和纹理特征,根据烟雾、火焰的图像特征与森林图像特征的不同,来分析识别烟雾、火焰信息,并在GIS中自动识别并定位火点。     

Growth of Phlebiopsis gigantea in wood of seven conifer species

Heterobasidion parviporum and Heterobasidion annosum are widely distributed root‐rot fungi that infect conifers throughout Europe. Infection of conifer stumps by spores of these pathogens can be controlled by treating fresh stumps with a competing non‐pathogenic fungus, Phlebiopsis gigantea. In this study, growth of three Latvian strains of P. gigantea and the biological control agent ‘Rotstop’ strain was evaluated in stem pieces of Norway spruce, Scots pine, lodgepole pine, Douglas‐fir, Weymouth pine, Siberian larch and Sitka spruce. The growth rates of one H. parviporum and one H. annosum isolate were also measured in the same stem pieces. The growth rate of P. gigantea varied greatly in wood of different conifer species. It was higher in the three pine species, lower in Norway spruce and lowest in Sitka spruce and Siberian larch, and in Douglas‐fir, this fungus did not grow. The largest area of wood occupied by P. gigantea was in lodgepole pine. Growth of Latvian isolates of P. gigantea in the wood of Pinus and Picea species was comparable to that of the Rotstop isolate. Consequently, stump treatment with local P. gigantea isolates should be recommended. However, our results suggest that Douglas‐fir stump treatment against Heterobasidion by P. gigantea may be ineffective and other stump treatment methods should be considered.     

Growth of Mixed Birch-Coniferous Stands in Relation to Pure Coniferous Stands at Similar Sites in South-eastern Norway

Mean age, mean and top heights and yield were studied in 20 mixed stands of birch ( Betula pubescens Ehrh. and B. pendula Roth) and Picea abies (L.) Karst. and nine mixed stands of birch and Pinus sylvestris L. in south-eastern Norway. Each mixed stand and the adjacent pure coniferous stand (control) were growing under the same site conditions and had not been commercially thinned. There were no significant differences in mean age at breast height or in top heights between birch and conifers in the mixed stands, while mean height was significantly higher for birch than for spruce. A growth index was calculated based on total volume and age at breast height. For the spruce sites the growth in young mixed stands (birch < 17 m) was superior to that of pure spruce, while the difference was insignificant in older stands. The growth index correlated positively with the ratio between generatively and vegetatively regenerated birch trees, and negatively with the age of the oldest species in the mixture and with site quality. For the pine sites there was no significant difference in the growth index between mixed birch-pine and pure pine stands. A mixture effect of birch on the volume yield of spruce or pine could not be demonstrated.     

Defoliation by the Needle-shortening Pine Gall Midge,Thecodiplosis brachyntera,on Pines in Central Sweden

An outbreak of the needle-shortening pine gall midge, Thecodiplosis brachyntera , occurred on Scots pine, Pinus sylvestris (L.) and lodgepole pine, P. contorta (Dougl.) in central Sweden during 1995-1998. The larval feeding of T. brachyntera kills current-year needles and heavy infestation causes severe defoliation. A pattern of fluctuating defoliation among years and sites was found on both pine species. Defoliation was evenly distributed in the crown of P. sylvestris during years of high as well as low infestation; apical whorls had as much defoliation as basal whorls. In P. contorta , however, there was a tendency for defoliation to be concentrated on branches in the most apical whorls. Growth ring increments on P. sylvestris with high levels of defoliation (71%) did not differ from trees with moderate levels (26%) of defoliation. Shoot lengths were significantly shorter, however, on heavily infested trees the year after defoliation.     

Boron in forest trees and forest ecosystems

This review critically examines the role of boron (B) in forests in view of recent findings on B nutrition and the continuing occurrence of B deficiency. Many perceptions about the role of B in plants and its uptake and mobility have been altered since the last review on B in forest trees in 1990. Now there is evidence for a fundamental role of B in the formation of the pectic structure in primary cell walls in plants, and further roles in membrane function are being explored. In plants, channel-mediated B uptake, active B uptake and B uptake by mycorrhizas have been shown, B transporters have been identified, and B retranslocation has been shown. We explore these findings and their consequences on forest trees and on ecosystems that they dominate. Particular emphasis is placed on B retranslocation and B in mycorrhizal symbiosis, given their importance in trees.     

Survival and Growth of Picea abies Regeneration after Shelterwood Removal with Single- and Double-grip Harvester Systems

Three stands in Sweden were followed for 7 yrs to study the survival and growth of Norway spruce [Picea abies (L.) Karst.] regeneration after shelterwood removal with single- and double-grip harvester systems. The height of all seedlings within circular plots was recorded before and after final cutting. The tallest seedling and one randomly selected seedling on each circular plot were permanently marked and their annual height growth was measured each year during the period 1993-1999. No significant differences between single- and double-grip harvester systems were found with respect to their effects on regeneration density, survival or annual height growth. The annual height growth of the individual seedlings after shelterwood removal was significantly correlated with seedling height before shelterwood removal. Significant differences were found in annual height growth between seedlings with high and low vitality. Logging damage did not affect the annual height growth. Several practical conclusions were drawn. First, the choice of harvester system does not affect seedling height growth or survival after shelterwood removal. Secondly, the removal of a 200 m³ shelterwood with 200 stems ha^-1 does not seem to constitute a serious problem for seedling survival and growth. Finally, estimated vitality and seedling height both seem to be fairly good predictors of postrelease survival and growth.     

Development of Pinus sylvestris Main Stems Following Three Different Precommercial Thinning Methods in a Mixed Stand

Reducing competition by point cleaning may be an attractive alternative to conventional precommercial thinning in forestry. In this study, survival and development of main stems of Scots pine (Pinus sylvestris L.) following point cleaning were examined in a mixed stand of mainly Scots pine and birch (Betula pendula Roth and Betula pubescens Ehrh.) in northern Sweden. Treatments studied were: no precommercial thinning, conventional precommercial thinning, point cleaning of all secondary stems, and point cleaning of only the secondary stems that were higher than the main stem, within a radius of 0.8 m from the main stem, respectively. A randomised complete block design with three replicates was used. Measurements taken 13 growing seasons after these treatments showed that conventional precommercial thinning was the best treatment for retaining Scots pines as main stems. However, conventional precommercial thinning resulted in the poorest timber quality of the remaining Scots pines in terms of stem taper, thickest branch diameter and relative live crown height. In conclusion, point cleaning has to be followed by a complementary cleaning operation if the objective is to retain Scots pines as main stems in such mixed stands.     

Tree planting for dryland salinity control in Australia

Dryland salinity is emerging as a major form of land and water degradation in southern Australia, particularly in Western Australia, South Australia and Victoria, and to a lesser extent in New South Wales, Tasmania and Queensland.Tree planting, in combination with other vegetation treatments, is regarded as a leading solution to dryland salinity. Research has now shown that planting trees can significantly lower groundwater tables, and thereby reverse the causal process of salinisation. Substantial progress has been made towards answering the basic questions of which species to grow, how to plant, where to plant, at what density and configuration to plant, and how much area to plant. The economic potential for commercial tree planting has given impetus to partial reforestation in higher rainfall (> 600 mm yr^–1) areas. Even so, serious constraints are apparent, relating primarily to cost, uncertainty and attitude. The future should bring increasing community input and control, technical refinement and gradual adoption, provided all aspects of the issue are well researched, relevant information is well communicated and programmes are well administered. Some specific requirements for future research are identified in this review.     

Effect of Cuttings on the Scenic Beauty of a Tree Stand

The opinions of 207 respondents on the visual effects of seven different cutting types were asked using a nine-point verbal scale ranging from ''worsens very much'' to ''improves very much''. Other estimates were obtained by letting the same respondents evaluate photographs of stands which had been treated with different cuttings. The direct questions gave results quite similar to the evaluations of photographs for all but young respondents, indicating that most respondents were able to imagine the effect of the treatment correctly. The results based on the evaluation of photographs indicated that the effect of regenerative cuttings is negative while the impact of thinnings is positive. After a few years of cutting the stand is already regarded as clearly more pleasant than immediately after the cutting. Natural regeneration with seed trees seems to be a way to avoid the very negative immediate impact of clear-felling, especially in the case of Scots pine. Women, young, urban people and those who do not own forest or have work related to forests tended to experience thinnings less positively and saw regenerative cuttings as more harmful than the other test groups did.     

Pinus contorta growth in northern Sweden as affected by soil scarification

The aim of this study was to quantify the effects of different soil scarification methods on tree growth. Soil scarification influenced stem volume and stem biomass yield of lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) in a 17-year-old field trial in boreal Sweden. Soil scarification (disc trenching, mounding and ploughing) resulted in an average stem volume yield of 3.1 and 34.2 m³ ha^–1 on the poor and intermediate sites, respectively, while corresponding values for no soil scarification were 0.9 and 16.7 m³ ha^–1. In comparison to no scarification, ploughing increased volume yields by 500% on the poor site and by 200% on the intermediate sites. The ranking according to stem volume yield was ploughing > disc trenching = mounding no soil scarification. Averaged over the two sites, the mean annual increment of stem biomass was 219% and 145% higher (in d.w., 0.26 kg and 0.34 kg per sample tree) after ploughing compared with no soil scarification, for the average and dominant sample trees, respectively. Although not significant, the increased growth rate after soil scarification decreased the average stem basic wood density of the sample trees with 1.6% and 5.3%, at the poor and intermediate sites, respectively. In conclusion, soil scarification significantly increased the 17-year stem volume yield compared with no scarification. The results also indicate that the difference in stem biomass yield between ploughing and the other methods, especially no soil scarification, will increase even more in the near future.