干涉SAR相位解缠中的枝切策略分析

二维相位解缠是合成孔径雷达干涉测量数据处理中的关键步骤和难点,通过对现有相位枝切解缠算法的枝切连接策略进行分析,并结合最小生成树的原理,提出了一种最优最小生成树相位解缠的方法,很大程度地减少了以往方法中造成地枝切线过多、过长、闭合等弊病的发生,阻止了由于枝切线设置错误所引起的误差传播,既保持了枝切法速度快的特点,又优化了算法。通过几种方案的对比实验,说明该方法能提高相位解缠精度。     

一种MBR约束下的高分光学影像直角建筑物提取与标绘方法

针对高空间分辨率遥感影像中建筑物信息提取与标绘问题,提出了一种MBR约束下的高分光学影像中直角建筑物信息提取与标绘方法。首先采用多尺度影像对象分割与CART决策树分类技术,提取影像中的建筑物区域;其次用Candy算子提取出建筑物的粗轮廓,并将其转化为点集形式表示;然后通过轮廓点集计算建筑物最小外包矩形（MBR）,对建筑物的轮廓进行分段拟合与优化;最后通过交点方向决策器确定建筑物的角点,依次连接各角点实现建筑物的标绘。通过计算建筑物的面积与周长,确定周长相对精度为93.3%,面积相对精度为96.1%,本文方法可以有效提高建筑物的标绘精度。     

Employing ground and satellite-based QuickBird data and random forest to discriminate five tree species in a Southern African Woodland

With the emergence of very high spatial and spectral resolution data set, the resolution gap that existed between remote-sensing data set and aerial photographs has decreased. The decrease in resolution gap has allowed accurate discrimination of different tree species. In this study, discrimination of indigenous tree species (n?=?5) was carried out using ground based hyperspectral data resampled to QuickBird bands and the actual QuickBird imagery for the area around Palapye, Botswana. The purpose of the study was to compare the accuracies of resampled hyperspectral data (resampled to QuickBird sensors) with the actual image (QuickBird image) in discriminating between the indigenous tree species. We performed Random Forest (RF) using canopy reflectance taking from ground-based hyperspectral sensor and the reflectance delineated regions of the tree species. The overall accuracies for classifying the five tree species was 79.86 and 88.78% for both the resampled and actual image, respectively. We observed that resampled data set can be upscale to actual image with the same or even greater level of accuracy. We therefore conclude that high spectral and spatial resolution data set has substantial potential for tree species discrimination in savannah environments.     

Tree species biomass and carbon stock measurement using ground based-LiDAR

This study scrutinises the use of terrestrial laser scanning (TLS) to measure diameter at breast height (DBH) and tree height at individual tree species level. LiDAR point cloud scans are collected from uniformly defined control points. The result of processed TLS data demonstrates the precise measurements of tree height and DBH by comparing it with field data (DBH, tree height, tree species and location). The average tree height and DBH obtained through TLS measurements were 9.44?m and 43.30?cm, respectively. A linear equation between TLS derived parameters and field measured values were established, which gave the coefficient of determination (r2) of 0.79 and 0.96 for tree height and DBH, respectively. Further, these parameters were used to calculate above ground biomass (AGB) for individual tree species by considering a non-destructive approach. The total AGB and carbon stock from 80 different trees are computed to be 49.601 and 22.320?tonnes, respectively.     

云计算环境下空间索引构建研究

空间数据索引对于空间数据管理和分析具有重要作用,与数据处理速度和效率密切相关。随着人类社会进入大数据时代,遥感矢量数据具备了大数据的特点,传统的空间索引构建方法无法有效满足矢量大数据处理的需求,为此引入云计算环境来进行空间索引构建,目的是提高空间索引构建速度。首先,对常见的空间索引及现阶段云计算环境下基于MapReduce模型的空间数据管理进行了综述;然后以云计算环境下R树索引构建为例,对云计算环境下空间索引的构建进行了研究;最后,通过实验验证,证明了云计算环境下空间索引构建的速度与单机索引构建相比,加速比为28~40倍;在相同云环境下,网格索引构建速度最快,R+索引构建速度相对较慢。     

树轮记录的过去359a阿勒泰地区初夏气温变化

利用采集自阿尔泰山南坡森林上限3个采样点的西伯利亚落叶松(Larix sibirica Ledeb.)树芯样本,研制其树轮宽度年表。与区域内6个气象站点观测数据的相关分析结果表明,标准化宽度年表与6月平均气温相关较好,最高相关系数达0.675（p<0.0001）。使用逐步回归分析方法,建立温度的重建方程,调整自由度后的方差解释量为45.6%（1962~2012年）。过去359年来,阿勒泰地区平均气温变化存在7个偏暖（1667~1681年、1714~1728年、1747~1779年、1787~1800年、1862~1887年、1935~1968年、2000~2012年）和6个偏冷阶段（1682~1713年、1729~1746年、1780~1786年、1801~1861年、1888~1934年、1969~1999年）。并存在5个温暖年、54个偏暖年、252个正常年、37个偏冷年、以及11个寒冷年。6月平均温度的最高值出现在1830年（22.35℃）,最低温度出现在1985年（17.87℃）。功率谱分析显示该重建序列存在30.0年、7.4年的显著准周期（p<0.05）和6.4年的较显著准周期（p<0.10）。     

Transpiration in Quercus suber trees under shallow water table conditions: the role of soil and groundwater

Water is one of the major environmental factors limiting plant growth and survival in the Mediterranean region. Quercus suber L. woodlands occupy vast areas in the Iberian Peninsula, frequently under shallow water table conditions. The relative magnitude of soil and groundwater uptake to supply transpiration is not easy to evaluate under these circumstances. We recently developed a conceptual framework for the functioning of the root system in Q. suber that simulates well tree transpiration, based on two types of root behaviour: shallow connected and deep connected. Although this significantly improved knowledge on the functional traits of Mediterranean Q. suber, the approach has the limitation of requiring root sap flow data, which are seldom available. In this work, we present alternative methodologies to assess if trees are connected to groundwater and to estimate the soil and groundwater contributions to tree transpiration. We provide evidence on the tree unrestricted access to groundwater solely based on meteorological, stem sap flow and leaf water potential data. Using a soil mass balance approach, we estimated the yearly soil and groundwater contributions to tree transpiration: 69.7% and 30.3%, respectively. Groundwater uptake became dominant in the dry summer: 73.2% of tree transpiration. Results reproduce extremely well those derived from root modelling. Because of its simplicity both in formulation and data requirements, our approach is potentially liable to be adapted to other groundwater‐dependent Mediterranean oak sites, where interactions between land use and water resources may be relevant. Copyright © 2013 John Wiley & Sons, Ltd.     

A multi‐species dendroclimatic reconstruction of Chilko River streamflow,British Columbia,Canada

Dendroclimatological data were used to reconstruct the discharge history of Chilko River, which drains a glacierized watershed in the Coast Mountains of British Columbia. We correlated ring‐width records from Engelmann spruce (ES) (Picea engelmanni) and mountain hemlock (MH) (Tsuga mertensiana) trees to historical hydroclimate data. Over the period of record, spruce and hemlock radial growth correlates significantly with temperature and snow depth, respectively. We found that a multi‐species approach provided a better model fit and reconstructive power. Using these relationships, we developed generalized linear models for mean June, July, and June‐July discharge. The proxy records provide insights into streamflow variability of a typical Coast Mountains river over the past 240 years and confirm the long‐term influence of the Pacific Decadal Oscillation (PDO) on hydroclimatic regimes in the region. A relationship also exists between the reconstructed June‐July discharge record and the North Pacific (NP) Index, suggesting that winter atmospheric patterns over the North Pacific influence the hydrology of coastal British Columbia. Copyright © 2010 John Wiley & Sons, Ltd.     

RAPID applied to the SIM‐France model

SIM‐France is a large connected atmosphere/land surface/river/groundwater modelling system that simulates the water cycle throughout metropolitan France. The work presented in this study investigates the replacement of the river routing scheme in SIM‐France by a river network model called RAPID to enhance the capacity to relate simulated flows to river gauges and to take advantage of the automated parameter estimation procedure of RAPID. RAPID was run with SIM‐France over a 10‐year period and results compared with those of the previous river routing scheme. We found that while the formulation of RAPID enhanced the functionality of SIM‐France, the flow simulations are comparable in accuracy to those previously obtained by SIM‐France. Sub‐basin optimization of RAPID parameters was found to increase model efficiency. A single criterion for quantifying the quality of river flow simulations using several river gauges globally in a river network is developed that normalizes the square error of modelled flow to allow equal treatment of all gauging stations regardless of the magnitude of flow. The use of this criterion as the cost function for parameter estimation in RAPID allows better results than by increasing the degree of spatial variability in optimization of model parameters. Likewise, increased spatial variability of RAPID parameters through accounting for topography is shown to enhance model performance. Copyright © 2011 John Wiley & Sons, Ltd.