Use of local and global maps of forest canopy height and aboveground biomass to enhance local estimates of biomass in miombo woodlands in Tanzania     

《International Journal of Applied Earth Observation and Geoinformation》2020

Field surveys are often a primary source of aboveground biomass (AGB) data, but plot-based estimates of parameters related to AGB are often not sufficiently precise, particularly not in tropical countries. Remotely sensed data may complement field data and thus help to increase the precision of estimates and circumvent some of the problems with missing sample observations in inaccessible areas. Here, we report the results of a study conducted in a 15,867 km² area in the dry miombo woodlands of Tanzania, to quantify the contribution of existing canopy height and biomass maps to improving the precision of canopy height and AGB estimates locally. A local and a global height map and three global biomass maps, and a probability sample of 513 inventory plots were subject to analysis. Model-assisted sampling estimators were used to estimate mean height and AGB across the study area using the original maps and then with the maps calibrated with local inventory plots. Large systematic map errors – positive or negative – were found for all the maps, with systematic errors as great as 60–70 %. The maps contributed nothing or even negatively to the precision of mean height and mean AGB estimates. However, after being calibrated locally, the maps contributed substantially to increasing the precision of both mean height and mean AGB estimates, with relative efficiencies (variance of the field-based estimates relative to the variance of the map-assisted estimates) of 1.3–2.7 for the overall estimates. The study, although focused on a relatively small area of dry tropical forests, illustrates the potential strengths and weaknesses of existing global forest height and biomass maps based on remotely sensed data and universal prediction models. Our results suggest that the use of regional or local inventory data for calibration can substantially increase the precision of map-based estimates and their applications in assessing forest carbon stocks for emission reduction programs and policy and financial decisions.  相似文献   

一种基于M估计的Robust-ELM滑坡位移预测方法     

高彩云  高宁 《大地测量与地球动力学》2019,39(2):153-157

采用传统ELM算法进行滑坡位移预测时，其网络输出权值由最小二乘估计得出，导致ELM抗差能力较差，从而造成网络训练参数不准确。为此，将M估计与ELM相结合，提出一种基于M估计的Robust-ELM滑坡变形预测方法。该方法利用加权最小二乘方法来取代最小二乘法计算ELM输出权值，以减少滑坡监测数据中粗差对ELM预测的干扰。分别以链子崖、古树屋滑坡体为例，将Robust-ELM进行了单维、多维粗差的抵御性验证。结果表明，该方法能够有效降低粗差对预测的影响，具有良好的抗差能力。  相似文献   

建筑物侧面轮廓线约束的高分辨率遥感影像建筑物高度估算方法     

陈辉  张卡  宿东  王蓬勃 《测绘通报》2019,(9):34-37,72

针对现有利用阴影长度法提取建筑物高度时存在的阴影间相互遮挡问题，提出了一种基于建筑物侧面轮廓线进行建筑物高度估算的新方法。首先，利用RPC模型计算建筑物像点位移的方向与卫星成像角度，再将遥感影像进行旋转，使建筑物像点位移沿水平方向；然后，利用Canny算法进行轮廓检测，并构建一定长度的矩形形态学结构元素，对轮廓图像进行形态学开运算，以提取侧面轮廓线，再利用Hough变换与建筑物角点约束，对所提取的轮廓线进一步筛选；最后，根据卫星侧视成像时建筑物高度与像点位移的几何关系进行建筑物的高度估算。利用实际的高分辨率卫星影像对本文方法进行了验证，并与阴影法估算建筑物高度进行了对比。试验结果证明，利用建筑物侧面轮廓线进行建筑物高度估算平均误差可以达到0.7 m，且实际精度优于使用阴影法进行建筑物高度估算。  相似文献   

Indoor localization for pedestrians with real-time capability using multi-sensor smartphones     

Catia Real Ehrlich 《地球空间信息科学学报》2019,22(2):73-88

ABSTRACT

The localization of persons or objects usually refers to a position determined in a spatial reference system. Outdoors, this is usually accomplished with Global Navigation Satellite Systems (GNSS). However, the automatic positioning of people in GNSS-free environments, especially inside of buildings (indoors) poses a huge challenge. Indoors, satellite signals are attenuated, shielded or reflected by building components (e.g. walls or ceilings). For selected applications, the automatic indoor positioning is possible based on different technologies (e.g. WiFi, RFID, or UWB). However, a standard solution is still not available. Many indoor positioning systems are only suitable for specific applications or are deployed under certain conditions, e.g. additional infrastructures or sensor technologies. Smartphones, as popular cost-effective multi-sensor systems, is a promising indoor localization platform for the mass-market and is increasingly coming into focus. Today’s devices are equipped with a variety of sensors that can be used for indoor positioning. In this contribution, an approach to smartphone-based pedestrian indoor localization is presented. The novelty of this approach refers to a holistic, real-time pedestrian localization inside of buildings based on multi-sensor smartphones and easy-to-install local positioning systems. For this purpose, the barometric altitude is estimated in order to derive the floor on which the user is located. The 2D position is determined subsequently using the principle of pedestrian dead reckoning based on user's movements extracted from the smartphone sensors. In order to minimize the strong error accumulation in the localization caused by various sensor errors, additional information is integrated into the position estimation. The building model is used to identify permissible (e.g. rooms, passageways) and impermissible (e.g. walls) building areas for the pedestrian. Several technologies contributing to higher precision and robustness are also included. For the fusion of different linear and non-linear data, an advanced algorithm based on the Sequential Monte Carlo method is presented.  相似文献   

海州湾4种鱼类生长特征的空间异质性     

王琨  张崇良  王晶  任一平 《海洋学报》2019,41(12):62-70

传统的渔业资源评估均假设鱼类的生长参数是匀质的，然而近年来越来越多的研究表明海洋鱼类生长存在空间异质性。为探究海州湾鱼类生长参数的空间异质性现象，本研究分析了2013–2018年海州湾及其邻近海域方氏云鳚(Pholis fangi)、尖海龙(Syngnatus acus)、小黄鱼(Larimichthys polyactis)和赤鼻棱鳀(Thryssa kammalensis)的空间分布，使用电子体长频率分析方法结合Bootstrap重抽样方法估算了这4种鱼类的生长参数及其在深、浅水区域中的差异。结果显示，这4种鱼类生长参数均表现出一定的空间异质性，其中尖海龙和小黄鱼生长参数的空间异质性表现较为明显。这种差异可能是由于空间上的理化条件、群落结构以及物种本身洄游分布的差异而产生的。  相似文献   

Some remarks on Q-compensated sparse deconvolution without knowing the quality factor Q     

Xintao Chai  Ronghua Peng  Genyang Tang  Wei Chen  Jingnan Li 《Geophysical Prospecting》2019,67(8):2003-2021

The subsurface media are not perfectly elastic, thus anelastic absorption, attenuation and dispersion (aka Q filtering) effects occur during wave propagation, diminishing seismic resolution. Compensating for anelastic effects is imperative for resolution enhancement. Q values are required for most of conventional Q-compensation methods, and the source wavelet is additionally required for some of them. Based on the previous work of non-stationary sparse reflectivity inversion, we evaluate a series of methods for Q-compensation with/without knowing Q and with/without knowing wavelet. We demonstrate that if Q-compensation takes the wavelet into account, it generates better results for the severely attenuated components, benefiting from the sparsity promotion. We then evaluate a two-phase Q-compensation method in the frequency domain to eliminate Q requirement. In phase 1, the observed seismogram is disintegrated into the least number of Q-filtered wavelets chosen from a dictionary by optimizing a basis pursuit denoising problem, where the dictionary is composed of the known wavelet with different propagation times, each filtered with a range of possible values. The elements of the dictionary are weighted by the infinity norm of the corresponding column and further preconditioned to provide wavelets of different values and different propagation times equal probability to entry into the solution space. In phase 2, we derive analytic solutions for estimates of reflectivity and Q and solve an over-determined equation to obtain the final reflectivity series and Q values, where both the amplitude and phase information are utilized to estimate the Q values. The evaluated inversion-based Q estimation method handles the wave-interference effects better than conventional spectral-ratio-based methods. For Q-compensation, we investigate why sparsity promoting does matter. Numerical and field data experiments indicate the feasibility of the evaluated method of Q-compensation without knowing Q but with wavelet given.  相似文献   

基于遗传算法优化BP神经网络的玉米遥感估产方法     

于海洋  陈圣波  杨北萍  安秦 《世界地质》2020,39(1):208-214

以内蒙古自治区开鲁县玉米作物为研究对象,将生育期内玉米遥感影像所提取的多种植被指数和实地采样点的测产数据作为训练值,利用BP(back propagation)神经网络和遗传算法优化BP(GA-BP)神经网络估产模型,得出网络预测的玉米产量数值。通过决定系数R 2和均方根误差RMSE,比较实测产量与预测产量之间的精度,BP神经网络模型R^2为0.8452,RMSE(%)为28.37;遗传算法优化BP神经网络模型R^2为0.9850,RMSE(%)为6.70,表明遗传算法优化BP神经网络估产模型具有一定可行性和可信度。  相似文献   

基于共轭梯度搜索的病态问题处理方法     

刘杰  张娟娟 《大地测量与地球动力学》2019,39(8):863-868

在最小二乘平差准则基础上，把病态平差问题转化为无约束的二次规划问题，并利用优化理论分析病态对平差解的影响。通过共轭梯度搜索算法在可行域中寻找最优步长因子，自动寻找最速下降方向，并给出迭代初值的设置方法。分析近似计算中病态问题与局部最优解的关系，讨论局部最优解的快速迭代方法，并通过实例验证算法的有效性，计算迭代的速度。由于整个过程没有对法方程系数矩阵进行求逆计算，该算法可用于处理大规模系数矩阵高病态的平差问题。  相似文献   

运用H、O同位素分析石阡地区地热水来源     

李永康  陈正山  王甘露 《水文》2021,41(1):28-34

通过对贵州省石阡地区地热水、冷泉及河流的地热地质条件、水化学成分及氢氧同位素分析,对该地区的地热水、冷泉及河流的水化学特征、来源及石阡地区的补给模式进行了研究。温泉水属于低中矿化度的弱碱性水;温泉群中阳离子以Ca^2+、Mg^2+为主,阴离子以SO4^2-和HCO3^-为主,研究区水化学类型主要为HCO3-Ca和SO4.HCO3-Ca型。区域内地热水中δ18O值为-9.32‰~-6.81‰,δD为-64.4‰~-44.9‰;冷泉及河流中δ18O值为-7.51‰~-6.00‰,δD为-50.7‰~-38.2‰,均分布在我国大气降水线及当地大气降水线附近,表明该地区主要是大气降水成因。通过H、O同位素计算补给区温度,地热水补给高程,以及冷泉及河流补给高程,推测出补给区可能为袍木寨背斜一带及红石走滑断裂及其断裂束附近的碳酸盐岩裸露地区。氚盈余参数d表明石阡地区大多数地热水埋深较浅,循环径流时间较短,地质环境处于开放与半开放之间,水-岩反应作用相对较弱。  相似文献   

花岗岩风化料弃土快速堆填过程中不排水抗剪强度评估     

詹良通  孙倩倩  郭晓刚  陈锐  陈云敏 《岩土力学》2021,(1):50-58

沿海沿江城市地下开挖产生的工程渣土含泥量大、含水率高且较松散,主要运往渣土场进行堆填处置。由于产量巨大而处置场地有限,许多渣土场在运营过程中存在堆填速度快、缺乏排水设施、超高超库容堆填等问题,容易引发堆填体失稳事故。目前对于非饱和工程渣土堆体在快速堆填过程中的失稳机制认识尚不清晰,尤其是对这一过程中的高饱和度工程渣土强度增长规律缺乏足够的认识。以深圳红坳渣土场填料——花岗岩风化料(CDG)填土为研究对象,对不同初始饱和度土样进行三轴不排水不排气等向压缩和剪切试验,结果表明:非饱和CDG填土不排水抗剪强度随围压增大呈非线性增长,增长速率与试样初始饱和度密切相关;当土样压缩后的饱和度超过0.7,不排水强度随围压的增长速率显著降低。基于有效固结应力法的原理,结合Hilf孔压公式和修正剑桥模型,提出了一种工程渣土不排水抗剪强度估算方法,并通过与试验结果对比验证了该方法对初始饱和度高于0.6的CDG填土的适用性。利用该方法确定的不排水强度cu与正应力σn的关系可应用于高饱和度工程渣土快速堆填中的稳定性分析。  相似文献