A Double Sodium Layer(DSL) structure was observed during the night of August 22, 2011 over Haikou,China(20°N,110°E) by Na lidar.This DSL comprised a typical sodium layer at altitudes of 80～105km and a highe...A Double Sodium Layer(DSL) structure was observed during the night of August 22, 2011 over Haikou,China(20°N,110°E) by Na lidar.This DSL comprised a typical sodium layer at altitudes of 80～105km and a higher sodium layer at altitudes of 105～115km in about 0.5 h.A wavelength of 589 nm dye laser pumped by a Nd:YAG laser was used to make the measurement. The backscattered fluorescence photons from the sodium layer were collected by a telescope with a primary mirror of 1000 mm in diameter.The sodium density of these layers during the nighttime observation in the Mesosphere and Lower-Thermosphere(MLT) was studied.展开更多
【目的】针对传统机载激光雷达(Light Detection And Ranging,LiDAR)所生成的冠层高度模型分辨率较低,不利于高郁闭度人工针叶林中冠幅较小的树种单木分割的问题,基于大疆禅思L1激光雷达高密度点云,提出了一种基于层次化泛洪的单木分割...【目的】针对传统机载激光雷达(Light Detection And Ranging,LiDAR)所生成的冠层高度模型分辨率较低,不利于高郁闭度人工针叶林中冠幅较小的树种单木分割的问题,基于大疆禅思L1激光雷达高密度点云,提出了一种基于层次化泛洪的单木分割算法。【方法】采用大疆禅思L1激光雷达设备,选择东北地区樟子松与兴安落叶松人工林作为实验样地。首先对原始的高密度激光雷达点云依次进行拼接、去噪、高程归一化处理,针对两块样地生成分辨率分别为0.1、0.2、0.4 m的高、中、低3种分辨率的冠层高度模型。对3种冠层高度模型分别进行先开后闭的形态学滤波处理,以降低冠层高度模型中单个树冠内部不同像素间高程差。然后采用反距离插值算法对3种冠层高度模型中的空洞像素进行平滑处理,并采用图像增强算法提高3种冠层高度模型中树冠内部像素与树冠间像素的对比度,以降低形态学滤波对林隙的模糊处理影响。最后利用局部最大值法分别在3种冠层高度模型中搜索树顶,基于搜索到的树顶位置,结合分层处理思想通过模拟泛洪算法实现单木分割,并基于一般树冠形态,对分割后树冠投影形状、面积进行约束,以优化分割后树冠形状。【结果】针对人工针叶林林分,提出的单木分割算法结合高分辨率冠层高度模型在两种树种样地下最高分割精度达到90%以上。其中,在冠幅较小的兴安落叶松样地中,基于高、中、低分辨率冠层高度模型的单木分割精度F值分别达到91.6%、85.9%、80.2%。而冠幅较大的樟子松样地中,基于高、中、低分辨率冠层高度模型的单木分割精度F值分别为86.2%、84.1%、75.9%。【结论】基于冠层高度模型的单木分割场景中,冠幅较大的树种对于一定范围内分辨率变化不敏感,高分辨率冠层高度模型可以提高人工针叶林单木分割精度,尤其是对于冠幅较小的树种分割精度提高较大。本研究提出的单木分割方法结合无人机高密度LiDAR点云在高郁闭度人工针叶林样地中可达到较高分割精度。展开更多
Based on the dual-wavelength lidar we have developed, the 24 h continuous ob- servation has been realized in its sodium channel by using Faraday atomic filter technology and other relevant technologies. This will faci...Based on the dual-wavelength lidar we have developed, the 24 h continuous ob- servation has been realized in its sodium channel by using Faraday atomic filter technology and other relevant technologies. This will facilitate the continuous ob- servation of the sodium layer and the relevant upper atmosphere over Wuhan. A result of about 50 h observation indicates that the daytime column density of so- dium layer over Wuhan is slightly increased compared to that during the nighttime, and the characteristics of the sporadic sodium layer occurring during the daytime are compared with that during the nighttime.展开更多
Based on observations from daytime lidars in eastern China,diurnal cycles of the sodium layer over Wuhan(30.5°N,114.6°E)and Beijing(40.5°N,116°E)are investigated.Diurnal variations of Na density,ro...Based on observations from daytime lidars in eastern China,diurnal cycles of the sodium layer over Wuhan(30.5°N,114.6°E)and Beijing(40.5°N,116°E)are investigated.Diurnal variations of Na density,root mean square(RMS)layer width,and centroid height of the sodium layer are analyzed.Results reveal that the large diurnal cycles of the sodium layer are controlled mainly by 24-hr oscillations at the two observation sites.The diurnal variation of the sodium layer over Wuhan was modulated mainly by tidal perturbations during the lidar observation campaign.Conversely,the diurnal variation over Beijing was controlled principally by photoionization and photochemistry effects during another campaign,and there was little evidence of direct tidal perturbations.These comparisons suggest that the diurnal variation of the sodium layer perhaps has obvious regional characteristics across China.The variation can be either controlled mainly by tidal perturbations or by photoionization and photochemistry effects in different seasons.展开更多
Voxel-based canopy profiling is commonly used to determine small-scale leaf area.Layer thickness and voxel size impact accuracy when using this method.Here,we determined the optimal combination of layer thickness and ...Voxel-based canopy profiling is commonly used to determine small-scale leaf area.Layer thickness and voxel size impact accuracy when using this method.Here,we determined the optimal combination of layer thickness and voxel size to estimate leaf area density accurately.Terrestrial LiDAR Stonex X300 was used to generate point cloud data for Masson pines(Pinus massoniana).The canopy layer was stratified into 0.10-1.00-m-thick layers,while voxel size was 0.01-0.10 m.The leaf area density of individual trees was estimated using leaf area indices for the upper,middle,and lower canopy and the overall canopy.The true leaf area index,obtained by layered harvesting,was used to verify the inversion results.Leaf area density was inverted by nine combinations of layer thickness and voxel size.The average relative accuracy and mean estimated accuracy of these combined inversion results exceeded 80%.When layer thickness was 1.00 m and voxel size 0.05 m,inversion was closest to the true value.The average relative accuracy was 92.58%,mean estimated accuracy 98.00%,and root mean square error 0.17.The combination of leaf area density and index was accurately retrieved.In conclusion,nondestructive voxel-based canopy profiling proved suitable for inverting the leaf area density of Masson pine in Hetian Town,Fujian Province.展开更多
Here is the first report on the observation of meteor ablation trails with lidar in China. Four long-lived Na ablation trails were observed during the 18/19 Nov. 2001 Leonid meteor shower with a sodium resonance lidar...Here is the first report on the observation of meteor ablation trails with lidar in China. Four long-lived Na ablation trails were observed during the 18/19 Nov. 2001 Leonid meteor shower with a sodium resonance lidar over Wuhan. The mean altitude of the 4 trails is 97.95 km, consistent with Leouid high entry velocity (-72km/s). The peak density averages about 3380±3633cm^-3, and the abundance is (2.33±1.49)×10^8cm^-2 ,both of which are higher than those previously observed for sporadic meteor trails. The RMS width is 359 m and the meteor's age is 81 min, indicating that they are long duration meteor trails. These observation results are quite different from those of sporadic meteor trails, but comparable to the 1998 and 1999 Leonid report.Five night observations from 17 Nov. to 23 Nov. suggest that the 2001 Leouid meteor shower does not have a significant impact on the abundance of the background Na layer.展开更多
Sodium layers (75–105 km) were measured by Na lidar on three nights during March 1–3, 1996. The lidar data were used to calculate the relative atmospheric density perturbations and their spectra. The average r. m. s...Sodium layers (75–105 km) were measured by Na lidar on three nights during March 1–3, 1996. The lidar data were used to calculate the relative atmospheric density perturbations and their spectra. The average r. m. s. density perturbations for early March at Wuhan are 5 %. The vertical wave number spectra exhibit power-law shapes with an average slope of -2.23 in the upper mesosphere when the associated mean density quantity of the day was used.展开更多
基金Supported by High Education Research of the Education Department of Hainan Province(Hjkj2012-21)Specialized Research Fund for State Key Laboratories(Y02211J82S,Y02211A49S)
文摘A Double Sodium Layer(DSL) structure was observed during the night of August 22, 2011 over Haikou,China(20°N,110°E) by Na lidar.This DSL comprised a typical sodium layer at altitudes of 80～105km and a higher sodium layer at altitudes of 105～115km in about 0.5 h.A wavelength of 589 nm dye laser pumped by a Nd:YAG laser was used to make the measurement. The backscattered fluorescence photons from the sodium layer were collected by a telescope with a primary mirror of 1000 mm in diameter.The sodium density of these layers during the nighttime observation in the Mesosphere and Lower-Thermosphere(MLT) was studied.
文摘【目的】针对传统机载激光雷达(Light Detection And Ranging,LiDAR)所生成的冠层高度模型分辨率较低,不利于高郁闭度人工针叶林中冠幅较小的树种单木分割的问题,基于大疆禅思L1激光雷达高密度点云,提出了一种基于层次化泛洪的单木分割算法。【方法】采用大疆禅思L1激光雷达设备,选择东北地区樟子松与兴安落叶松人工林作为实验样地。首先对原始的高密度激光雷达点云依次进行拼接、去噪、高程归一化处理,针对两块样地生成分辨率分别为0.1、0.2、0.4 m的高、中、低3种分辨率的冠层高度模型。对3种冠层高度模型分别进行先开后闭的形态学滤波处理,以降低冠层高度模型中单个树冠内部不同像素间高程差。然后采用反距离插值算法对3种冠层高度模型中的空洞像素进行平滑处理,并采用图像增强算法提高3种冠层高度模型中树冠内部像素与树冠间像素的对比度,以降低形态学滤波对林隙的模糊处理影响。最后利用局部最大值法分别在3种冠层高度模型中搜索树顶,基于搜索到的树顶位置,结合分层处理思想通过模拟泛洪算法实现单木分割,并基于一般树冠形态,对分割后树冠投影形状、面积进行约束,以优化分割后树冠形状。【结果】针对人工针叶林林分,提出的单木分割算法结合高分辨率冠层高度模型在两种树种样地下最高分割精度达到90%以上。其中,在冠幅较小的兴安落叶松样地中,基于高、中、低分辨率冠层高度模型的单木分割精度F值分别达到91.6%、85.9%、80.2%。而冠幅较大的樟子松样地中,基于高、中、低分辨率冠层高度模型的单木分割精度F值分别为86.2%、84.1%、75.9%。【结论】基于冠层高度模型的单木分割场景中,冠幅较大的树种对于一定范围内分辨率变化不敏感,高分辨率冠层高度模型可以提高人工针叶林单木分割精度,尤其是对于冠幅较小的树种分割精度提高较大。本研究提出的单木分割方法结合无人机高密度LiDAR点云在高郁闭度人工针叶林样地中可达到较高分割精度。
基金Supported by the National Basic Research Program of China (Grant No. G2000078400)
文摘Based on the dual-wavelength lidar we have developed, the 24 h continuous ob- servation has been realized in its sodium channel by using Faraday atomic filter technology and other relevant technologies. This will facilitate the continuous ob- servation of the sodium layer and the relevant upper atmosphere over Wuhan. A result of about 50 h observation indicates that the daytime column density of so- dium layer over Wuhan is slightly increased compared to that during the nighttime, and the characteristics of the sporadic sodium layer occurring during the daytime are compared with that during the nighttime.
基金financially supported by the National Natural Science Foundation of China(Grant No.41264006)the China Postdoctoral Science Foundation(Grant No.20110490609)+1 种基金the Natural Science Foundation of Hainan Province(Grant Nos.413127,20154191)partially supported by the National Natural Science Foundation of China(Grant Nos.40905012,41174129)
文摘Based on observations from daytime lidars in eastern China,diurnal cycles of the sodium layer over Wuhan(30.5°N,114.6°E)and Beijing(40.5°N,116°E)are investigated.Diurnal variations of Na density,root mean square(RMS)layer width,and centroid height of the sodium layer are analyzed.Results reveal that the large diurnal cycles of the sodium layer are controlled mainly by 24-hr oscillations at the two observation sites.The diurnal variation of the sodium layer over Wuhan was modulated mainly by tidal perturbations during the lidar observation campaign.Conversely,the diurnal variation over Beijing was controlled principally by photoionization and photochemistry effects during another campaign,and there was little evidence of direct tidal perturbations.These comparisons suggest that the diurnal variation of the sodium layer perhaps has obvious regional characteristics across China.The variation can be either controlled mainly by tidal perturbations or by photoionization and photochemistry effects in different seasons.
基金This research was funded by Fujian University Industry-University Cooperation Project(grant number 2019N5012)Remote Sensing Quantitative Simulation of Rainfall Erosion Reduction Function of Forest Vertical Structure(grant number 31770760).
文摘Voxel-based canopy profiling is commonly used to determine small-scale leaf area.Layer thickness and voxel size impact accuracy when using this method.Here,we determined the optimal combination of layer thickness and voxel size to estimate leaf area density accurately.Terrestrial LiDAR Stonex X300 was used to generate point cloud data for Masson pines(Pinus massoniana).The canopy layer was stratified into 0.10-1.00-m-thick layers,while voxel size was 0.01-0.10 m.The leaf area density of individual trees was estimated using leaf area indices for the upper,middle,and lower canopy and the overall canopy.The true leaf area index,obtained by layered harvesting,was used to verify the inversion results.Leaf area density was inverted by nine combinations of layer thickness and voxel size.The average relative accuracy and mean estimated accuracy of these combined inversion results exceeded 80%.When layer thickness was 1.00 m and voxel size 0.05 m,inversion was closest to the true value.The average relative accuracy was 92.58%,mean estimated accuracy 98.00%,and root mean square error 0.17.The combination of leaf area density and index was accurately retrieved.In conclusion,nondestructive voxel-based canopy profiling proved suitable for inverting the leaf area density of Masson pine in Hetian Town,Fujian Province.
文摘Here is the first report on the observation of meteor ablation trails with lidar in China. Four long-lived Na ablation trails were observed during the 18/19 Nov. 2001 Leonid meteor shower with a sodium resonance lidar over Wuhan. The mean altitude of the 4 trails is 97.95 km, consistent with Leouid high entry velocity (-72km/s). The peak density averages about 3380±3633cm^-3, and the abundance is (2.33±1.49)×10^8cm^-2 ,both of which are higher than those previously observed for sporadic meteor trails. The RMS width is 359 m and the meteor's age is 81 min, indicating that they are long duration meteor trails. These observation results are quite different from those of sporadic meteor trails, but comparable to the 1998 and 1999 Leonid report.Five night observations from 17 Nov. to 23 Nov. suggest that the 2001 Leouid meteor shower does not have a significant impact on the abundance of the background Na layer.
文摘Sodium layers (75–105 km) were measured by Na lidar on three nights during March 1–3, 1996. The lidar data were used to calculate the relative atmospheric density perturbations and their spectra. The average r. m. s. density perturbations for early March at Wuhan are 5 %. The vertical wave number spectra exhibit power-law shapes with an average slope of -2.23 in the upper mesosphere when the associated mean density quantity of the day was used.
文摘使用Nd:YAG激光器和泵浦染料激光器产生的589 nm激光,与中高层大气中钠原子产生共振,利用直径为1000 mm的望远镜接收钠层的光子回波.研究中国海口市2010年5月4日夜间的中高层大气中钠层密度分布,计算钠层的相对密度和绝对密度,研究钠层密度峰值变化.观测到突发钠层出现在23:52 LT,持续12 min.
