Mitigating systematic error in topographic models derived from UAV and ground‐based image networks          下载免费PDF全文

Mike R. James  Stuart Robson 《地球表面变化过程与地形》2014,39(10):1413-1420

High resolution digital elevation models (DEMs) are increasingly produced from photographs acquired with consumer cameras, both from the ground and from unmanned aerial vehicles (UAVs). However, although such DEMs may achieve centimetric detail, they can also display systematic broad‐scale error that restricts their wider use. Such errors which, in typical UAV data are expressed as a vertical ‘doming’ of the surface, result from a combination of near‐parallel imaging directions and inaccurate correction of radial lens distortion. Using simulations of multi‐image networks with near‐parallel viewing directions, we show that enabling camera self‐calibration as part of the bundle adjustment process inherently leads to erroneous radial distortion estimates and associated DEM error. This effect is relevant whether a traditional photogrammetric or newer structure‐from‐motion (SfM) approach is used, but errors are expected to be more pronounced in SfM‐based DEMs, for which use of control and check point measurements are typically more limited. Systematic DEM error can be significantly reduced by the additional capture and inclusion of oblique images in the image network; we provide practical flight plan solutions for fixed wing or rotor‐based UAVs that, in the absence of control points, can reduce DEM error by up to two orders of magnitude. The magnitude of doming error shows a linear relationship with radial distortion and we show how characterization of this relationship allows an improved distortion estimate and, hence, existing datasets to be optimally reprocessed. Although focussed on UAV surveying, our results are also relevant to ground‐based image capture. © 2014 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

Sea‐level rise impact on fresh groundwater lenses in two‐layer small islands          下载免费PDF全文

Hamed Ketabchi  Davood Mahmoodzadeh  Behzad Ataie‐Ashtiani  Adrian D. Werner  Craig T. Simmons 《水文研究》2014,28(24):5938-5953

The fresh groundwater lenses (FGLs) of small islands can be highly vulnerable to climate change impacts, including sea‐level rise (SLR). Many real cases of atoll or sandy islands involve two‐layer hydrogeological conceptualizations. In this paper, the influential factors that affect FGLs in two‐layer small islands subject to SLR are investigated. An analytical solution describing FGLs in circular islands, composed of two geological layers, is developed for the simplified case of steady‐state and sharp‐interface conditions. An application of the developed model is demonstrated to estimate the FGL thickness of some real‐world islands by comparison with existing FGL thickness data. Furthermore, numerical modelling is applied to extend the analysis to consider dispersion effects and to confirm comparable results for both cases. Sensitivity analyses are used to assess the importance of land‐surface inundation caused by SLR, relative to other parameters (i.e. thickness of aquifer layers, hydraulic conductivity, recharge rate and land‐surface slope) that influence the FGL. Dimensionless parameters are used to generalize the findings. The results demonstrate that land‐surface inundation has a considerable impact on a FGL influenced by SLR, as expected, although the FGL volume is more sensitive to recharge, aquifer thickness and hydraulic conductivity than SLR impacts, considering typical parameter ranges. The methodology presented in this study provides water resource managers with a rapid‐assessment tool for evaluating the likely impacts of SLR and accompanying LSI on FGLs.  相似文献   

便携式消费级无人机相机标定有效性评估   总被引：1，自引：0，他引：1  

李冀  熊晶  熊保颂  吴星宇  张朝阳  李雪 《测绘通报》2021,(4):131-135

本文针对近年来在各行业中广泛使用的便携式消费级无人机开展了相机标定有效性研究,分别通过室内标定场和后处理软件对相机进行标定和自标定,在对比无相机标定、飞前相机标定、飞后相机标定和自标定迭代校正等方法所得成图精度后,对不同相机标定方案的有效性进行了评估。结果表明：各种方案成图总体精度差别不大;飞前、飞后相机标定与无相机标定的成图精度相当;自标定迭代校正的成图精度略高于其他方案。可见采用航拍照片自标定参数迭代校正的方法更适合于飞行控制精度和成像系统稳定性都不高的便携式消费级无人机相机标定。  相似文献   

梵净山地区板溪群红子溪组钙质岩系中大理岩透镜体成因探讨     

彭成龙  陈建书  杨凯迪 《贵州地质》2011,(4):286-289

梵净山地区板溪群红子溪组钙质岩系中广泛发育大理岩透镜体。形成此岩系的控制因素可能为振荡频繁的构造运动或气候条件。通过仔细观察,发现大理岩透镜体有条带状、似层状断续产出2种,初步认为透镜体是成岩过程中差异性压实作用的产物,不是某种环境沉积的透镜体。  相似文献   

Geologic and hydrologic settings for development of freshwater lenses in arid lands   总被引：2，自引：0，他引：2       下载免费PDF全文

Adam Milewski  Mohamed Sultan  Ahmad Al‐Dousari  Eugene Yan 《水文研究》2014,28(7):3185-3194

Satellite observations were used to test the validity of previously identified favourable conditions for the formation of freshwater lenses, identify additional potential occurrences, and model modern potential recharge in the Raudhatain Watershed (3696) in northern Kuwait. Favourable conditions include infrequent yet intensive precipitation events, drainage depressions to collect the limited runoff, and presence of conditions (e.g. high infiltration capacity) that promote groundwater recharge and preservation (e.g. underlying saline aquifer) of infiltrating groundwater as freshwater lenses floating over saline aquifer water due to differences in density. Specifically, the following field and satellite‐based observations were noted for the Raudhatain Watershed: (1) Over ~30 precipitation events were identified from the Tropical Rainfall Measuring Mission precipitation data (1998–2009); (2) slope is gentle (2 m/km), and the surface is largely (80%) covered by alluvial deposits with high infiltration capacities (up to 9 m/day); (3) no flows and long‐term ponding were reported at the watershed outlet or detected from Landsat thematic mapper images; (4) infiltration is high based on increases in soil moisture content (from an advanced microwave scanning radiometer) and vegetation index following large precipitation events; and (5) freshwater lenses that overlie highly saline [total dissolved solids (TDS): >35 000] unconfined aquifers underlying the watershed are absent in the southern regions, where infiltrating fresh water mixes with the less saline groundwater (TDS: <10 000). Twenty potential locations (size: 1 to 75 km²) for freshwater lens development were identified in northern Kuwait, and continuous rainfall–runoff models (Soil Water and Assessment Tool) were applied to provide a first‐order estimation of the average annual recharge in the watershed (127 × 10⁶ m³) and freshwater lenses (8.17 × 10⁶ m³). Results demonstrate the settings for enhanced opportunities for groundwater recharge, outline the amounts of and preservation conditions for the groundwater feeding the freshwater lenses, and highlight potential applications and locations of freshwater lenses in similar settings elsewhere in the Arabian Peninsula and beyond. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

折射/谐衍射红外双波段成像光谱仪系统研究     

刘英  孙强  卢振武  曲锋  吴宏圣  李淳 《海洋学报》2010,32(10):6980-6987

为了获取足够的目标信息,充分利用中波红外和长波红外的光谱信息,建立了谐衍射中、长波红外超光谱成像系统.利用谐衍射元件独特的色散特性,将谐衍射透镜应用于中、长波红外超光谱成像系统中,使系统在中波红外3.7—4.8 μm和长波红外8—12 μm的2个红外大气窗口内获取数百个光谱图像.设计结果表明,中波红外波段,在18对线/mm处光学系统的调制传递函数(MTF)大于0.55;长波红外波段,在13对线/mm处光学系统的MTF大于0.5;光学系统的衍射环绕能,在中波红外波段30 μm半径范围内大于85%,在长波红外  相似文献   

Structure of Subsurface Intrusion of the Oyashio Water into the Kuroshio Extension and Formation Process of the North Pacific Intermediate Water     

Kuniaki Okuda  Ichiro Yasuda  Yutaka Hiroe  Yugo Shimizu 《Journal of Oceanography》2001,57(2):121-140

In order to understand the actual formation process of the North Pacific Intermediate Water (NPIW), structure of subsurface intrusions of the Oyashio water and the mixing of the Oyashio and the Kuroshio waters in and around the Kuroshio Extension (KE) were examined on the basis of a synoptic CTD observation carried out in May-June 1992. The fresh Oyashio water in the south of Hokkaido was transported into KE region through the Mixed Water Region (MWR) in the form of subsurface intrusions along two main paths. The one was along the east coast of northern Japan through the First Branch of the Oyashio (FBO) and the other along the eastern face of a warm streamer which connected KE with a warm core ring through the Second Branch of the Oyashio (SBO). The fresh Oyashio water extended southward through FBO strongly mixed with the saline NPIW transported by the Kuroshio in the south of Japan (old NPIW) in and around the warm streamer. On the other hand, the one through SBO well preserved its original properties and extended eastward beyond 150°E along KE with a form of rather narrow band. The intrusion ejected Oyashio water lens with a diameter of 50–60 km southward across KE axis and split northward into the MWR involved in the interaction of KE and a warm core ring, which were supposed to be primary processes of new NPIW formation.  相似文献   

一种适用于视频全站仪的数码相机检校方法     

田浩  蒋理兴  张强 《海洋测绘》2005,25(2):61-63

直接线性变换法是相机检校中常用的一种方法，在此基础上提出一种可应用于视频全站仪的数码相机检校方法，通过改变像方元素的单位，就可不必考虑标准单位和像素单位间的转化因子问题。进一步讨论了像素尺寸大小对系统误差的影响，并对像素大小的必要测定精度进行了公式推导。试验结果表明，该方法可以获得较好的校准结果。  相似文献   

光学显微镜成像方式及投影冷光源的分频合成探讨     

赵应权  沈忠民  王鹏 《岩矿测试》2014,33(5):674-680

传统显微镜光源主要包括卤素灯光源、纯水过滤热射线光源、LED光源等,由于卤素灯光源含有大量760~1400 nm区段的红外线,纯水过滤热射线光源滤除红外线不彻底且水会导致透射光线的部分散射,LED光源在500 nm波长附近的光照强度不足、波形存在缺陷,容易灼伤样品或使成像质量受限,都难以满足需要采用大功率冷光源进行无损、高质量显微观察成像和测试的要求。本文在总结光学显微镜的成像方式、光源类型及各类光源优缺点的基础上,提出了采用三棱镜-凸透镜组分频合成冷光源的新思路。该思路首先利用三棱镜将卤素灯光源光谱按频率顺序打开,然后选择可见光区域内的光谱,用凸透镜组校正可见光方向后,再由三棱镜将这些可见光合成不含热射线的冷光源。理论和砂岩荧光薄片实际测试效果表明,该方法既可完全排除热射线,从而使样品免遭受破坏,又保持了完整的可见光光谱,解决了大功率冷光源红外线生热和光谱存在缺陷的难题,这为采用大功率冷光源的光学显微镜投影高质量成像提供了新的方法及切实可行的依据。该套分频合成光源的装置主要配置为:玻璃材质的同规格的三棱镜与凸透镜各两个,卤素灯光源一个。结构简单,可在需使用大功率冷光源进行无损成像和测试等方面获得广泛的应用。  相似文献   

海岛淡水透镜体演变规律的室内模拟实验     

甄黎  周从直  束龙仓  曹英杰  耿海涛 《吉林大学学报(地球科学版)》2008,38(1):81-85

淡水透镜体作为海岛主要的甚至是唯一的淡水资源,对其在天然和开采条件下的演变规律研究是海岛淡水资源利用和管理的首要任务。采用自制的室内物理模型,对海岛淡水透镜体的演变过程进行了模拟实验。模拟了降雨补给条件下淡水透镜体的形成过程;在无补给条件下,开采淡水时倒锥的变化过程。结果表明:当开采量达到3.73×10-5m3/s时,倒锥进入抽水井,淡水透镜体被击穿。  相似文献