地形坡面对被动微波遥感影响的试验研究

地表起伏所形成的倾斜表面,特别是在山区,受地形坡度和坡向变化的影响,地表的微波辐射特征较之平坦地表发生明显变化。基于地基微波辐射地形试验,模拟星载被动微波辐射计AMSR\|E的观测参数,通过建立地形坡面的地貌微缩景观进行观测,探索地表斜坡对被动微波辐射特征的影响,用AIEM模型 和 Fresnel 方程分别模拟裸土地形坡面的微波辐射特征。结果表明,倾斜坡面对被动微波辐射的亮度温度产生了10~15 K的偏差,由坡度形成的本地入射角改变了地表的有效发射率,并随坡向的变化发生微波极化旋转。经试验数据和模型模拟结果对比,认为AIEM 在考虑了表面粗糙度影响时可以较好地模拟地形坡面的被动微波辐射特征。     

Evaluating and comparing performances of topographic correction methods based on multi-source DEMs and Landsat-8 OLI data

Topographic correction is a crucial and challenging step in interpreting optical remote-sensing images of extremely complex terrain environments due to the lack of universally suitable correction algorithms and digital elevation models (DEMs) of adequate resolution and quality. The free availability of open source global DEMs provides an unprecedented opportunity to remove topographic effects associated with remote-sensing data in remote and rugged mountain terrains. This study evaluated the performances of seven topographic correction methods including C-correction (C), Cosine C-correction (CC), Minnaert correction (M), Sun–canopy–sensor (SCS) correction (S), SCS+C-correction (SC), Teillet regression correction (TR), and the Terrain illumination correction model (TI) based on multi-source DEMs (local topographic map, Shuttle Radar Topography Mission (SRTM) DEM filled-finished A/B and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) global digital elevation model (GDEM) data sets) and Landsat-8 Operational Land Imager (OLI) data using visual and statistical evaluation strategies. Overall, these investigated topographic correction methods removed topographic effects associated with Landsat-8 OLI data to varying degrees. However, the performances of these methods generally depend on the use of different DEMs and evaluation strategies. Among these correction methods, the SCS+C-correction performed best and was less sensitive to the use of different DEMs. The performances of topographic corrections based on free and open-access DEMs were generally better than or comparable to those based on local topographic maps. In particular, the topographic correction performance was greatly improved using the SRTM filled-finished B (FFB) data set with a resampling scheme based on the average value within a 3 × 3 pixel window. Nevertheless, further quantitative investigation is needed to determine the relative importance of DEMs and evaluation strategies used to select topographic correction methods.     

Accuracy assessment of the processed SRTM-based elevation data by CGIAR using field data from USA and Thailand and its relation to the terrain characteristics

Shuttle radar topographic mission (SRTM) has created an unparalleled data set of global elevations that is freely available for modeling and environmental applications. The global availability (almost 80% of the Earth surface) of SRTM data provides baseline information for many types of the worldwide research. The processed SRTM 90 m digital elevation model (DEM) for the entire globe was compiled by Consultative Group for International Agriculture Research Consortium for Spatial Information (CGIAR-CSI) and made available to the public via internet mapping interface. This product presents a great value for scientists dealing with terrain analysis, thanks to its easy download procedure and ready-to-use format. However, overall assessment of the accuracy of this product requires additional regional studies involving ground truth control and accuracy verification methods with higher level of precision, such as the global positioning system (GPS).The study presented in this paper is based on two independent datasets collected with the same GPS system in Catskill Mountains (New York, USA) and Phuket (Thailand). Both datasets were corrected with differential base station data. Statistical analysis included estimation of absolute errors and multiple regression analysis with slope and aspect variables. Data were analyzed for each location separately and in combination. Differences in terrain and geographical location allowed independent interpretation of results.The results of this study showed that absolute average vertical errors from CGIAR dataset can range from 7.58 ± 0.60 m in Phuket to 4.07 ± 0.47 m in Catskills (mean ± S.E.M.). This is significantly better than a standard SRTM accuracy value indicated in its specification (i.e. 16 m). The error values have strong correlation with slope and certain aspect values. Taking into account slope and aspect considerably improved the accuracy of the CGIAR DEM product for terrain with slope values greater than 10°; however, for the terrain with slope values less than 10°, this improvement was found to be negligible.     

Terrain visibility

Visibility indices, matrices, graphs, and maps are defined for digital elevation terrain models and their properties are established. Several potential applications of geometric terrain visibility in geographic information systems are presented. Direct applications include the location of observation points and hiding places, the determination of line-of-sight relay networks for microwave communications, scenic and hidden surface paths, and aids to navigation. Indirect applications allow inferences about physiographic terrain features: the mutual visibility among surface points yields considerable information about the landscape. The preservation of the visibility model also provides a check on data reduction (compression) in digital elevation models. Algorithms for computing terrain visibility on both triangulated irregular networks and rectangular grids are reviewed and experimental results from several sources are reported. It is shown that terrain visibility is invariant under certain projective transformations, and therefore relative elevations can be reconstructed from visibility maps.     

基于Landsat8热红外遥感数据的山地地表温度地形效应研究

地表温度是影响地表能量收支平衡的重要参量,能够综合反演地表的水热交换过程。虽然当前在基于地表温度开展全球或者区域尺度的地表能量平衡研究方面取得一系列的进展,但是面向山地区域尺度的类似研究仍然面临较大的挑战。为分析山地复杂地形对山地地表温度时空分布的影响规律,基于具有较高空间分辨率的Landsat 8热红外数据,以我国西南典型山地为研究对象,定量反演该区域的地表温度空间分布状况,结合SRTM90DEM数据,选择从海拔、坡度和坡向3个关键地形因子角度分析山地地表温度的地形效应特征。结果发现:山地地表温度随地形因子均呈现出十分显著的变化特征。总体而言,地表温度均随着海拔和坡度的升高而降低,而在坡向方面,南坡的温度相比北坡的温度要高。在地形效应分析的基础上,通过开展1km空间尺度地形和地表温度的空间统计分析发现,山地1km尺度下地表温度存在较大的空间异质性,且其影响不可忽略。研究结果表明:开展山地地表水热过程遥感动态监测需高空间分辨率地表温度作为数据支持,以准确描述山地地形因素对地表能量交换过程的影响。     

The topographic effect on LANDSAT data in gently undulating terrain in southern Sweden

Abstract

The purpose of this study was to investigate the effect of topography on LANDSAT satellite data in gently undulating terrain. Gently undulating terrain is in this work defined as terrain dominated by slopes of between 1° and 15°. For three various solar elevations (38°, 44° and 52°) digital LANDSAT MSS and TM data were merged with digital elevation data. In an agricultural region in southern Sweden 135 cultivated fields, 50 pasture sites and 117 forest sites with a total number of 88 800 pixels were studied.The relationship between LANDSAT response variation and topographic parameters within cultivated fields and forest areas was weak. For some pasture covers a topographic effect was identified.     

Incorporation of azimuthal control methods in the extraction of 3-dimensional topographic models from individual space-borne SAR scenes

Abstract

The radiometric variability of SAR images of rugged terrain is determined largely by surface orientation, specifically the range-directed component of terrain slope. This implies that although image shading information can be employed to derive elevation profiles for individual range lines, these profiles are decoupled due to the lack of azimuthal control. Two sources of azimuthal control are proposed which allow one to derive a 3-dimensional model of terrain for a SAR image swath. Range lines can be tied to an absolute coordinate grid through the use of an elevation transect or azimuthal control line (ACL). Slope integration away from the ACL will incur errors due to image speckle and radiometric calibration uncertainties. Periodic adjustment can be accomplished with the second source of control, a relative one, which employs lake levelling and the automated extraction and smoothing of valley floors. The above techniques have been utilized to derive terrain models from two Seasat subscenes. Over integration distances of 40 km, systematic and random components of error have been limited to 181 and 113 m, respectively. Although the derived DEMs are not of mapping quality they do provide useful, quantitative measures of the topographic shape of local scene features.     

Two models for evaluating landslide hazards

Two alternative procedures for estimating landslide hazards were evaluated using data on topographic digital elevation models (DEMs) and bedrock lithologies in an area adjacent to the Missouri River in Atchison County, Kansas, USA. The two procedures are based on the likelihood ratio model but utilize different assumptions. The empirical likelihood ratio model is based on non-parametric empirical univariate frequency distribution functions under an assumption of conditional independence while the multivariate logistic discriminant model assumes that likelihood ratios can be expressed in terms of logistic functions.The relative hazards of occurrence of landslides were estimated by an empirical likelihood ratio model and by multivariate logistic discriminant analysis. Predictor variables consisted of grids containing topographic elevations, slope angles, and slope aspects calculated from a 30-m DEM. An integer grid of coded bedrock lithologies taken from digitized geologic maps was also used as a predictor variable. Both statistical models yield relative estimates in the form of the proportion of total map area predicted to already contain or to be the site of future landslides. The stabilities of estimates were checked by cross-validation of results from random subsamples, using each of the two procedures. Cell-by-cell comparisons of hazard maps made by the two models show that the two sets of estimates are virtually identical. This suggests that the empirical likelihood ratio and the logistic discriminant analysis models are robust with respect to the conditional independent assumption and the logistic function assumption, respectively, and that either model can be used successfully to evaluate landslide hazards.     

MERC: a fortran iv program for the production of topographic data for the planet mercury

MERC provides the capability to construct cross sections or topographic maps for parts of the surface of the planet Mercury. The photometric theory that permits digital image brightness measurements from the Mariner 10 spacecraft to be converted into changes in surface topography elevations is described. Techniques for leveling or readjusting the slope of specific portions of a cross profile by multiple surface albedo estimates are discussed. We present several examples of crater cross sections and a topographic map.     

Downscaling MODIS-derived water maps with high-precision topographic data in a shallow lake

ABSTRACT

Remotely sensed imagery is the most efficient and widely used data source to monitor the water area changes. However, a trade-off always exists between temporal resolution and spatial resolution for satellite images. Taking the southern Dongting Lake as an example, this study was conducted to develop a method of downscaling the Moderate Resolution Imaging Spectroradiometer (MODIS)-derived coarse spatial resolution water maps in shallow lakes with high-precision digital elevation model. The main principle of the method is to identify and adjust the horizontal location errors of the waterlines extracted from coarse-resolution data by analysing and modifying the elevation leaps using finer-scale topography information. Moving average filter was used to smooth the errors of waterlines caused by the geometric inaccuracies and classification uncertainties of the coarse data. The optimal local window size of the moving average filter was selected automatically using an exponential decay function model and a curvature algorithm for each pixel in the waterlines. In reference to Landsat Thematic Mapper data, the accuracy of the downscaling result is distinctly higher than that of the original MODIS normalized difference water index-derived water maps. The presented method is proved to be an effective tool for acquiring water maps of shallow lake with high spatio-temporal resolution using coarse- or moderate-resolution satellite imagery and high-precision topographic data.     

地形坡度对INSAR系统参数设计的影响

利用干涉合成孔径雷达(INSAR)可以获取数字高程图(DEM)，为了得到高精度的DEM需要对干涉系统参数进行优化设计。通过对INSAR系统单视和多视处理时的测高误差分析，在考虑地形坡度的影响下，利用相同的准则对系统参数——天线视角、信号带宽和工作基线进行了优化设计，得出了最优参数随地形变化的规律性，并证明了单视和多视处理情况下优化设计的一致性，为干涉系统的合理设计和性能分析提供了理论指导。     

一种结合边缘检测的多基线InSAR高程反演方法

针对多基线InSAR高程重建算法鲁棒性差的问题,提出一种基于边缘检测与路径跟踪策略的多基线InSAR高程反演算法.该算法分为2个步骤.第1步是直接利用多基线最大似然估计算法从多幅不同基线的干涉相位图中获取粗略的地形高程,再用Sobel算子对滤波后的粗略地形高程进行边缘检测,获得地形的不连续边界;第2步则先构建优化的多基...     

Towards a framework for terrain attribute selection in environmental studies

Terrain attributes (e.g. slope, rugosity) derived from digital terrain models are commonly used in environmental studies. The increasing availability of GIS tools that generate those attributes can lead users to select a sub-optimal combination of terrain attributes for their applications. Our objectives were to identify sets of terrain attributes that best capture terrain properties and to assess how they vary with surface complexity. 230 tools from 11 software packages were used to derive terrain attributes from nine surfaces of different topographic complexity levels. Covariation and independence of terrain attributes were explored using three multivariate statistical methods. Distinct groups of correlated terrain attributes were identified, and their importance in describing a surface varied with surface complexity. Terrain attributes were highly covarying and sometimes ambiguously defined within software documentation. We found that a combination of six to seven particular terrain attributes always captures more than 70% of the topographic structure of surfaces.     

DEM保真精度定量化描述模型研究

等高线回放法是DEM精度评估的重要方法之一,可以用于检测地形的保真程度,但是现有定量评估指标属于相对保真精度的范畴。因此本文基于水系和地形的固有套合特性,提出了水系和地形套合隶属度函数,从两者的套合程度实现DEM保真精度的定量化描述。首先,根据线状要素位移准则、尺度准则、平均坡度准则、最大套合偏移量准则和目视效果准则,运用模糊数学方法建立水系和地形套合隶属度函数;然后,使用四个不同地貌类型实验区域的1:5万地形图作为基础源数据,实验分析了DEM保真精度的评估。实验结果表明水系和地形套合隶属度函数不仅可以用于DEM保真精度的定量评估,而且可以用于DEM最佳分辨率的确定以及DEM尺度转换的适宜范围的确定。     

Digital orthophotography: mapping with pictures

Aerial photographs and maps would seem a natural combination to record and analyze geographical information: maps provide geometric information and photographs add realistic, timely detail. But cameras record images on a flat plane, whereas the earth is curved and its terrain takes on many varied shapes-all of which distort the image geometry and render it invalid for mapping and geographic analysis. Digital orthophotographs solve this problem. A digital orthophoto starts with a rasterized (scanned) aerial photograph; a process called rectification (described below) removes distortions arising from the camera lens, the aircraft's position, and elevation and other topographical features. This transforms aerial photos into high-resolution digital images that correctly represent the geometry of an area and its terrain. These images can be used as standard true-scale representations of geographic sectors-a function already served by analog orthophotos, which must be painstakingly scanned and rectified in small strips or patches. Their fully digital format makes digital orthophotos useful as base maps in geographical information systems (GIS) used for creating and revising topographic and planimetric maps, vegetation and timber management, environmental impact assessments, and infrastructure assessment     

地形生成技术与方法的研究

三维地形生成与仿真有助于更好地理解地形结构和提高地理数据分析的水平,但由于实际地形起伏千差 万别,非常不规则,因此按给定条件进行地形的生成与仿真是非常困难的.本文把地形看成随机统计过程,将分形 几何模型与随机点生成技术及实用回归技术相结合,提出了一套切实可行的地形生成技术与方法,在给定地形特 征或地形参数(如平均高程、最大高程及其位置、最小高程及其位置、高程标准差、相关长度等)条件,通过模拟符合 地形统计特征的随机过程,即可通过计算机自动产生符合要求的“真实”的三维地形。模拟与仿真的结果证明了本 方法的可     

DEM保真精度定量化描述模型

等高线回放法是数字高程模型(DEM)精度评估的重要方法之一,可以用于检测地形的保真程度,但是现有定量评估指标属于相对保真精度的范畴,因此基于水系和地形的固有套合特性,提出了水系和地形套合隶属度函数,从两者的套合程度实现DEM保真精度的定量化描述.首先,根据线状要素位移准则、尺度准则、平均坡度准则、最大套合偏移量准则和目视效果准则,运用模糊数学方法建立水系和地形套合隶属度函数;然后,使用4个不同地貌类型实验区域的1∶5万地形图作为基础源数据,实验分析了DEM保真精度的评估.实验结果表明水系和地形套合隶属度函数不仅可以用于DEM保真精度的定量评估,而且可以用于DEM最佳分辨率的确定以及DEM尺度转换适宜范围的确定.     

Radiometric slope correction for forest biomass estimation from SAR data in the Western Sayani Mountains,Siberia

We investigated the possibility of using multiple polarization (SIR-C) L-band data to map forest biomass in a mountainous area in Siberia. The use of a digital elevation model (DEM) and a model-based method for reducing terrain effects was evaluated. We found that the available DEM data were not suitable to correct the topographic effects on the SIR-C radar images. A model-based slope correction was applied to an L-band cross-polarized (hv) backscattering image and found to reduce the topographic effect. A map of aboveground biomass was produced from the corrected image. The results indicated that multipolarization L-band synthetic aperture radar (SAR) data can be useful for estimation of total aboveground biomass of forest stands in mountainous areas.     

Satellite lidar vs. small footprint airborne lidar: Comparing the accuracy of aboveground biomass estimates and forest structure metrics at footprint level

The use of lidar remote sensing for mapping the spatial distribution of canopy characteristics has the potential to allow an accurate and efficient estimation of tree dimensions and canopy structural properties from local to regional and continental scales. The overall goal of this paper was to compare biomass estimates and height metrics obtained by processing GLAS waveform data and spatially coincident discrete-return airborne lidar data over forest conditions in east Texas. Since biomass estimates are derived from waveform height metrics, we also compared ground elevation measurements and canopy parameters. More specific objectives were to compare the following parameters derived from GLAS and airborne lidar: (1) ground elevations; (2) maximum canopy height; (3) average canopy height; (4) percentiles of canopy height; and (5) above ground biomass. We used the elliptical shape of GLAS footprints to extract canopy height metrics and biomass estimates derived from airborne lidar. Results indicated a very strong correlation for terrain elevations between GLAS and airborne lidar, with an r value of 0.98 and a root mean square error of 0.78 m. GLAS height variables were able to explain 80% of the variance associated with the reference biomass derived from airborne lidar, with an RMSE of 37.7 Mg/ha. Most of the models comparing GLAS and airborne lidar height metrics had R-square values above 0.9.