Exploring the stemflow dynamics and driving factors at both inter- and intra-event scales in a typical subtropical deciduous forest     

Haixia Zhang  Congsheng Fu  Aimin Liao  Can Zhang  Jiufu Liu  Niu Wang  Bin He 《水文研究》2021,35(3):e14091

Numerous efforts have been made to understand stemflow dynamics under different types of vegetation at the inter-event scale, but few studies have explored the stemflow characteristics and corresponding influencing factors at the intra-event scale. An in-depth investigation of the inter- and intra-event dynamics of stemflow is important for understanding the ecohydrological processes in forest ecosystems. In this study, stemflow volume (F_V), stemflow funnelling ratio (F_R), and stemflow ratio (F_%) from Quercus acutissima and Broussonetia papyrifera trees were measured at both inter- and intra-event scales in a subtropical deciduous forest, and the driving factors, including tree species and meteorological factors were further explored. Specifically, the F_V, F_R and F_% of Q. acutissima (52.3 L, 47.2, 9.6%) were lower than those of B. papyrifera (85.1 L, 91.2, 12.4%). The effect of tree species on F_V and F_% was more obvious under low intensity rainfall types. At the inter-event scale, F_V had a strong positive linear correlation with rainfall amount (G_P) and event duration (D_E) for both tree species, whereas F_R and F_% had a positive logarithmic correlation with G_P and D_E only under high-intensity, short-duration rainfall type. F_R and F_% were mainly affected by wind speed and the maximum 30-min rainfall intensity under low-intensity, long-duration rainfall type. At the intra-event scale, for both tree species, the mean lag time between the start of rainfall and stemflow was the shortest under high-intensity, short-duration rainfall type, while the mean duration and amount of stemflow after rain cessation were the greatest under high-amount, long-duration rainfall type. The relationship between stemflow intensity and rainfall intensity at the 5-min interval scale also depended greatly on rainfall type. These findings can help clarify stemflow dynamics and driving factors at both inter- and intra-event scales, and also provide abundant data and parameters for ecohydrological simulations in subtropical forests.  相似文献   

Numerical Simulation of Magnetic Reconnection Driven by the Laser Helmholtz Capacitor-coil Targets     

XU Shan-shan  MEI Zhi-xing  ZHONG Jia-yong  LIN Jun 《Chinese Astronomy and Astrophysics》2021,45(2):131-146

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射电望远镜远场区域强干扰源规避方法研究          下载免费PDF全文

李欢  刘奇  王娜  蔡明辉  王玥  朱春花  苏晓明 《天文学报》2021,62(6):61

随着频率使用率的提高, 射电天文台址地面或空间存在强电磁干扰致使望远镜接收机系统处于非线性状态. 为减少强电磁干扰的影响、提高天文观测效率, 提出了一种基于望远镜远场区域的强干扰源规避方法. 首先, 通过仿真分析确定的射电望远镜远场方向图, 结合望远镜与干扰源之间的位置关系, 分析了强电磁干扰到达射电望远镜焦点处的功率响应, 并依据接收机第2阶中频放大器性能参数, 确定射电望远镜处于非饱和状态的规避角度计算方法. 其次, 采用该方法计算分析了民航飞机对射电望远镜的影响, 若民航飞机上有主动发射的干扰源, 且不经过反射等传播现象, 当射电望远镜主波束轴偏开一定方向后, 可有效降低对射电望远镜的干扰强度.  相似文献   

Runoff response of a small agricultural basin in the argentine Pampas considering connectivity aspects     

María Guadalupe Ares  Marcelo Varni  Celio Chagas 《水文研究》2020,34(14):3102-3119

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柱顶层间隔震体系增量动力响应研究          下载免费PDF全文

袁梦醒  陈望  刘彦辉  谭平  金建敏 《地震工程学报》2020,42(4):872-880

针对悬臂柱顶有拉梁和无拉梁层间隔震体系的抗震性能问题,运用增量动力分析(IDA)方法进行弹塑性分析,模拟结构从弹性到弹塑性直至最后倒塌的全过程。通过调幅地震动得到相应的层间位移角及峰值加速度,分别绘制单条与多条IDA曲线分析拉梁对隔震结构动力响应的影响,研究两种结构的抗震性能。结果表明:在相同性能点,有拉梁和无拉梁对纤维铰弯矩值和曲率值基本无影响,而在不同性能点,纤维铰状态明显不同;两种体系从正常使用阶段到防止倒塌阶段所需的加速度峰值的差距慢慢增大;在极罕遇地震下,柱顶有拉梁层间隔震体系的下部结构抗震性能要高于柱顶无拉梁层间隔震体系。  相似文献   

基岩倾角对盆地地震响应的影响分析          下载免费PDF全文

卓发成 《地震工程学报》2020,42(4):1035-1042

为了研究盆地基岩倾角对盆地地表动力反应的影响,选取了一个跨度2 km,深度500 m的二维成层盆地为研究对象进行有限元动力反应分析。以持时0.25 s的狄拉克脉冲作为输入地震动,探讨了P波和SV波垂直入射时,盆地基岩倾角从10°\,20°\,30°\,40°依次增加的情况下盆地地震反应。结果表明:入射波在倾斜基岩处发生波型转化,同时产生面波,在盆地中心区域发生汇聚;随着基岩倾角的增加地表中心处的卓越频率有减小的趋势。  相似文献   

The potential of Pléiades images with high angle of incidence for reconstructing the coastal cliff face in Normandy (France)     

《International Journal of Applied Earth Observation and Geoinformation》2020

To monitor chalk cliff face along the Normandy coast (NW France) which is prone to erosion, we tested the potential of cliff face 3D reconstruction using pairs of images with high angle of incidence at different dates from the agile Pléiades satellites. The verticality aspect of the cliff face brings difficulties in the 3D reconstruction process. Furthermore, the studied area is challenging mainly because the cliff face is north-oriented (shadow). Pléiades images were acquired over several days (multi-date stereoscopic method) with requested incidence angles until 40°. 3D reconstructions of the cliff face were compared using two software: ASP® and ERDAS IMAGINE®. Our results are twofold. Firstly, despite ASP® provides denser point clouds than ERDAS IMAGINE® (an average of 1.60 points/m² from 40° incidence angle stereoscopic pairs on the whole cliff face of Varengeville-sur-Mer against 0.77 points/m² respectively), ERDAS IMAGINE® provides more reliable point clouds than ASP® (precision assessment on the Varengeville-sur-Mer cliff face of 0.31 m ± 2.53 and 0.39 m ± 4.24 respectively), with a better spatial distribution over the cliff face and a better representation of the cliff face shape. Secondly, the quality of 3D reconstructions depends mostly on the amount of noise from raw images and on the shadow intensity on the cliff face (radiometric quality of images).  相似文献   

基于RTKLIB的低成本高精度GNSS静态测量系统     

董景利 《测绘通报》2020,(4):157-160

随着科学技术的发展，测量工具和测量手段也发生了变化，其中测量型GNSS呈现价格降低、体积缩小的趋势。目前市场上一整套商用GNSS测量系统的价格从几万到几十万不等，且由于地面基站和移动站体积大、携带不方便等原因，使得商用GNSS测量系统的使用人群仅限于部分专业测量人员，难以在大众市场普及。当今众多领域如无人机、机器制导、精密农业等对高精度定位需求的增加，又促使GNSS测量系统向低成本、高精度、小型化、轻型化发展。本文对U-BLOX的NEO-M8P低成本OEM型GNSS接收机进行50 km基线下的静态观测，基于RTKLIB的测试结果和精度分析表明，低成本GNSS测量系统能够达到厘米级定位精度，能够满足测量工作和GIS应用的需求。试验证明，使用此低成本测量系统能降低测量任务的经济成本，是测量级GNSS接收机中经济适用的选择。  相似文献   

基于像元二分模型的地表植被覆盖度估算模块化设计与实现     

赵威成  张红华  马福义  叶欣 《北京测绘》2020,(3):285-288

地表植被覆盖度是的一种应用广泛的定量遥感产品,在水文、生态、区域变化等方面都具有重要的意义。像元二分模型是应用最多的一种遥感估算地表覆盖度的方法。目前,用遥感的方法进行地表植被覆盖度估算没有完整、系统的工具,用户只能逐步进行操作,效率低下,鉴于上述情况,本文运用IDL交互式数据语言,基于ENVI二次开发了一个植被覆盖度估算程序,取得了一定的成效,对遥感定量产品的生产、应用具有一定意义。  相似文献   

基于空间句法理论的城市群核心区发展边界识别     

武凯华  李朝奎  刘俊杰  郝豪杰 《地理研究》2020,39(6):1418-1426

准确识别当前城市群建设进程中核心区发展边界是研究城市群的一项重要内容。本文提出一种研究思路：采用空间句法分析城市群道路网,将得到的4个分析指标融合成新指标——“城市群集群度”,并提取“城市群集群度”等值线和“城市群集群度”曲线,通过计算找到最佳阈值从而提取出城市群核心区发展边界。以长株潭城市群为例,将基于空间句法的研究结果与基于Densi-Graph方法的研究结果进行对比,在除去数据质量因素后,城市群核心区发展边界识别差异有望控制在10%以内。研究表明：基于空间句法理论的城市群核心区发展边界识别方法容易获取计算数据,适用范围广,可靠性强。  相似文献