结合DSM的机载LiDAR单木树高提取研究     

张海清  李向新  王成  习晓环  王濮  陈正宇 《地球信息科学学报》2021,23(10):1873-1881

机载LiDAR在提取地形坡度较大区域的冠层高度模型（CHM）时易产生畸变,降低单木树高的提取精度,为此提出一种CHM与数字表面模型（DSM）相结合的树高估算方法。首先基于预处理后的点云生成的CHM,利用局部最大值算法和标记控制分水岭分割算法进行分割,得到单木树冠轮廓多边形;然后结合DSM,采用固定窗口的局部最大值算法探测树顶点并提取其高程,继而与使用狄洛尼三角网和高程内插得到的地面点相减获取树高;最后,以广西兴安县富江村附近地形起伏较大的针叶林为试验区,测试3种不同坡度下,在CHM、CHM结合DSM获得的树高与实测树高分别进行精度分析。结果表明,当树木分别位于平均坡度为32°、27°和15°的试验区时,CHM中提取的树高与实测数据拟合的R²分别为0.84、0.85和0.87,RMSE为1.48、1.41和1.58 m,结合DSM后R²为0.92、0.91和0.93,RMSE为0.93、1.02和1.16 m;在地形坡度较大的区域,本文方法可以有效提高单木树高的估算精度。  相似文献   

中性层结下局地平缓地形起沙的次网格参数化研究     

赵建华  张强  隆霄 《气象学报》2013,71(4):731-742

局地地形起沙对沙尘模式的预报精度具有重要影响。基于狭管与下滑效应以及气流过山的已有研究成果,研究了中性层结与局地平缓地形条件下风速在这两种效应下次网格参数化问题,然后基于平坦地形的起沙公式、引入局地地形的摩擦速度,得到了相应的次网格起沙公式,最后对狭管效应、下滑效应以及两效应的叠加进行了理想试验。试验表明:(1)对于狭管效应的次网格参数化问题,风从狭管的阔口进(出)、窄口出(进)时,风速、跃移通量与起沙量均增大(减小);(2)下滑效应致使风速、跃移通量与起沙量均增大,且山脚增幅大于山坡;(3)对于两种效应的叠加,当气流从狭管的阔口进、窄口出时,风速、跃移通量和起沙量同时增大,山脚风速大于山坡,大粒径沙粒跃移通量增幅大于小粒径沙粒。反之,窄口进、阔口出时,出入口宽度之比存在一临界值,大于此临界值,风速减小;反之增大。而且,除了在山脚的小粒径沙粒在一定风速条件下跃移通量会增大外,其余情况均减少。最后,提出了本参数化方法与数值模式耦合的分算法与整算法。  相似文献   

Lapse Rate Adjustments of Gridded Surface Temperature Normals in an Area of Complex Terrain: Atmospheric Reanalysis versus Statistical Up-Sampling     

Alex J. Cannon  Denise Neilsen  Bill Taylor 《大气与海洋》2013,51(1):9-16

The applicability of elevation-regression based interpolation methods for long-term temperature normals, for example the Parameter-elevation Regressions on Independent Slopes Model (PRISM), becomes increasingly limited in data sparse, complex terrain such as that found in mountainous British Columbia (BC), Canada. Recent methods to improve both the resolution and accuracy of interpolation models have focused on the development of “up-sampling” algorithms based on local lapse rate adjustments to the original interpolated surfaces. Lapse rates can be derived from statistical models (e.g., elevation-based polynomial regression equations) or dynamical models (e.g., vertical temperature profiles from numerical weather prediction (NWP) models). This study compares a widely used statistical up-sampling algorithm, ClimateBC, with two NWP reanalysis products, the National Centers for Environmental Prediction/National Corporation for Atmospheric Research, Reanalysis 1 (NCEP1) and the more modern European Centre for Medium-range Weather Forecasts (ECMWF) Reanalysis Interim (ERA-Interim). Thirty-year climate normals for maximum and minimum temperatures were calculated using statistical up-sampling and NWP lapse rate adjustments to existing PRISM-based climate normals at a subset of stations in BC. Specifically, up-sampling model evaluation was performed using 1951–80 climate normals from an independent set of 54 surface stations (1 m to 2347 m) which were not included in the PRISM interpolation or assimilated into the NWP reanalysis products. All models performed similarly for minimum temperature, which showed only a slight improvement over PRISM. For maximum temperature, ClimateBC, NCEP1 and ERA-Interim all performed significantly better than PRISM, in particular during spring and summer. The ERA-Interim reanalysis outperformed NCEP1 in almost all months. The results suggest that lapse rate adjustment algorithms based on reanalysis products will have greater potential as progress continues on developing NWP components.

R ésumé ?[Traduit par la rédaction] L'application des techniques d'interpolation par régression en fonction de l'altitude pour les normales de température à long terme, comme le Parameter-elevation Regressions on Independent Slopes Model (PRISM), devient très difficile dans les régions accidentées pour lesquelles on dispose de données insuffisantes, par exemple les secteurs montagneux de la Colombie-Britannique (C.-B.) au Canada. Les toutes dernières méthodes destinées à augmenter le degré de résolution des modèles d'interpolation et leur précision reposent sur la conception d'algorithmes d’échantillonnage vertical fondés sur l'ajustement des surfaces interpolées originales au moyen du gradient vertical local. Nous pouvons établir les gradients verticaux à partir de modèles statistiques (p. ex., des équations de régression polynomiales en fonction de l'altitude) ou de modèles dynamiques (p. ex., des profils verticaux de température à partir de modèles de prévision numérique du temps (PNT)). Dans la présente étude, nous comparons un algorithme d’échantillonnage vertical statistique communément utilisé, le programme ClimateBC, à deux produits de réanalyse de PNT, celle des National Centres for Environmental Prediction/National Corporation for Atmospheric Research Reanalysis 1 (NCEP1), et la réanalyse provisoire (ERA-Interim) du Centre européen pour les prévisions météorologiques à moyen terme (ECMWF). Les normales climatiques de trente ans pour les températures maximums et minimums ont été calculées en appliquant la méthode d’échantillonnage vertical statistique et l'ajustement du gradient obtenu par PNT aux normales climatiques établies à partir du PRISM pour un sous-ensemble de stations en Colombie-Britannique. Plus particulièrement, nous avons procédé à l’évaluation du modèle d’échantillonnage vertical en nous servant des normales climatiques (1951–1980), pour un ensemble de 54 stations d'observation en surface indépendantes (1?m à 2347?m), exclues du modèle d'interpolation PRISM et des produits de réanalyse de PNT. Pour tous les modèles, nous avons obtenu des résultats comparables pour la température minimum, soit une légère amélioration seulement par rapport au PRISM. Pour la température maximum, nous avons obtenu avec ClimateBC, NCEP1 et ERA-Interim, des résultats nettement plus probants qu'avec PRISM, notamment au printemps et en été. Les réanalyses ERA-Interim ont donné de meilleurs résultats que NCEP1 pour pratiquement tous les mois. D'après ces résultats, le potentiel des algorithmes d'ajustements des gradients verticaux de température, établis à partir de produits de réanalyse se renforcera à mesure que les composantes de PNT se développeront.  相似文献   

Study of on‐site versus off‐site forecasts for Canadian Forces Base Summerside     

E.R. Lord  S. Ricketts 《大气与海洋》2013,51(1):95-105

Abstract

On‐site and off‐site forecasts for the CFB Summerside aerodrome, written coincidentally over a six‐week period, are verified using the Ranked Probability Score and compared by means of a two‐tailed test of paired differences. The results show that, at a 10% level of significance, forecasts made on‐site are significantly better than forecasts made off‐site for at least four hours into the forecast period. When compared with persistence, both forecast offices were superior. At no time did the persistence forecasts score significantly better than those issued by a meteorologist. When compared with climatology, on‐site forecasts were significantly better for the first nine hours, while off‐site forecasts were significantly better for the first ten hours.  相似文献   

A fast candidate viewpoints filtering algorithm for multiple viewshed site planning     

Yiwen Wang 《International journal of geographical information science》2020,34(3):448-463

ABSTRACT

The aim of site planning based on multiple viewshed analysis is to select the minimum number of viewpoints that maximize visual coverage over a given terrain. However, increasingly high-resolution terrain data means that the number of terrain points will increase rapidly, which will lead to rapid increases in computational requirements for multiple viewshed site planning. In this article, we propose a fast Candidate Viewpoints Filtering (CVF) algorithm for multiple viewshed site planning to lay a foundation for viewpoint optimization selection. Firstly, terrain feature points are selected as candidate viewpoints. Then, these candidate viewpoints are clustered and those belonging to each cluster are sorted according to the index of viewshed contribution (IVC). Finally, the candidate viewpoints with relatively low viewshed contribution rate are removed gradually using the CVF algorithm, through which, the viewpoints with high viewshed contribution are preserved and the number of viewpoints to be preserved can be controlled by the number of clusters. To evaluate the effectiveness of our CVF algorithm, we compare it with the Region Partitioning for Filtering (RPF) and Simulated Annealing (SA) algorithms. Experimental results show that our CVF algorithm is a substantial improvement in both computational efficiency and total viewshed coverage rate.  相似文献   

滆湖北部人工地形重塑下风浪场变化研究          下载免费PDF全文

秦灏  张怡辉  朱金格  胡维平  彭兆亮 《海洋与湖沼》2024,55(1):24-36

风浪是影响浅水湖泊物理生境环境重要的水动力要素之一。基于滆湖实测风浪数据, 建立了滆湖风浪模型, 验证结果表明模型可以较好模拟滆湖风浪随风场变化情况。在此基础上开展滆湖北部水域在人工地形重塑工程实施后的风浪变化情况分析。结果表明, 不同季节盛行风下, 风浪强度和湖底扰动强度均有一定程度的衰减, 这有利于水体透明度和水底光照条件的改善。风浪强度的衰减使得具有有利于水生植物生长与发育风浪条件的水域面积显著扩增。人工地形重塑的实施, 有利于滆湖北部水域水生植被物理生境环境改善, 从而为滆湖北部水域水生植被的修复提供较好的环境支撑, 也为其他浅水湖泊地形重塑工程的实施提供借鉴。  相似文献   

Statistical probability distribution of snow depth at the model sub‐grid cell spatial scale     

Wolf‐Dietrich Marchand  nund Killingtveit 《水文研究》2005,19(2):355-369

Comprehensive snow depth data, collected using georadar and hand probing, were used for statistical analyses of snow depths inside 1 km grid cells. The sub‐grid cell spatial scale was 100 m. Statistical distribution functions were found to have varying parameters, and an attempt was made to connect these statistical parameters to different terrain variables. The results showed that the two parameters mean and standard deviation of snow depth were significantly related to the sub‐grid terrain characteristics. Linear regression models could explain up to 50% of the variation for both of the snowcover parameters mentioned. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

空间数据的增值--以数字地形分析为例   总被引：1，自引：0，他引：1  

周启鸣  刘学军 《地理信息世界》2006,4(3):4-13

地理数据库的日益普及和空间数据的广泛传播使得过去由于数据的限制难以推广普及的地理信息技术有了一个崭新的发展空间。然而,目前大多数的实际应用仍停留在“数据”的层面,基本忽略了对数据本身内容的挖掘或“信息”提取,因而难以实现较高的数据应用效益和空间数据增值。本文以数字地形模型和数字地形分析为例,讨论空间数据的增值应用,通过利用地形分析技术从单纯的数字高程数据提取实际应用中急需的地形参数和地形特征信息,籍此说明空间数据增值应用的概念和内容。  相似文献   

The Beagle 2 stereo camera system     

A.D. Griffiths  A.J. Coates  J.-L. Josset  G. Paar  B. Hofmann  D. Pullan  P. Rüffer  M.R. Sims  C.T. Pillinger 《Planetary and Space Science》2005,53(14-15):1466-1482

The stereo camera system (SCS) was designed to provide wide-angle multi-spectral stereo imaging of the Beagle 2 landing site. Based on the Space-X micro-cameras, the primary objective was to construct a digital elevation model of the area in reach of the lander's robot arm. The SCS technical specifications and scientific objectives are described; these included panoramic 3-colour imaging to characterise the landing site; multi-spectral imaging to study the mineralogy of rocks and soils beyond the reach of the arm and solar observations to measure water vapour absorption and the atmospheric dust optical density. Also envisaged were stellar observations to determine the lander location and orientation, multi-spectral observations of Phobos & Deimos and observations of the landing site to monitor temporal changes.  相似文献   

中小型地质灾害由“防滑”治理向“放滑”排险方式转变研究：以广东中山为例     

牟元英 《江苏地质》2022,46(4):411-416

城镇城市化与城市地下空间开发给高精度重力探测技术的发展带来了良好机遇,从重力探测设备、高密度数据采集、精细数据处理和解释应用等方面介绍了高精度重力在城市地下空间探测研究应用取得的成果,包括重力仪精度及在干扰情况下的读数时间、三维坐标获取、地形改正方法、异常数据计算、反演方法及成果解释等,可对城市进行无损探测获取地下地质结构及特殊地质体分布信息,同时满足城市绿色环保勘探的要求,为城市空间探测挖掘重要地质信息提供了一种新的方法技术。  相似文献