Perspective terrain visualization—A fusion of remote sensing, GIS, and computer graphics

Techniques are presented that are used for the perspective visualization of natural landscapes in the field of environmental planning and civil engineering. In order to obtain a photo-realistic visual simulation, we use digital elevation models (DEM) and images generated by remote sensing techniques. The remote sensing systems used in this work include Landsat Thematic Mapper, SPOT HRV, and aerial photography. To achieve high quality perspective views, we first have to pay attention to an appropriate preprocessing of the remote sensing imagery. This includes radiometric corrections and image enhancement procedures as well as a precise geometric correction that is executed to achieve accurate coregistration of the different images with the terrain model. A mosaic of several images at different resolutions is stored, together with the DEM, in a database covering an extensive area. Projection software permits the user to specify all interior and exterior orientation parameters of a virtual camera to compute any perspective view. To obtain greater realism, atmospheric effects can also be simulated. Our visual simulation approach using a virtual scene permits automated image montage of 3D simulated objects. The achieved results show that this technology can be used in many different domains where terrain visualization is required.     

COMPUTER GRAPHICS AND REMOTE SENSING – A SYNTHESIS FOR ENVIRONMENTAL PLANNING AND CIVIL ENGINEERING

This paper presents efforts undertaken in the field of photo-realistic visualization of natural landscapes using digital elevation models (DEM) and images generated by remote sensing techniques. The remote sensing systems used in this work include Landsat Thematic Mapper, SPOT HRV and aerial photographs. After an appropriate preprocessing, including radiometric corrections and image enhancement procedures, a precise geometric correction is performed in order to achieve a very high co-registration of the images with the elevation model. A mosaic of several images at various resolutions is stored together with the DEM in a data set covering an extensive area. These data are then input to an efficient hardware-independent terrain rendering algorithm based on a forward projection. Atmospheric effects can be simulated. The concept of a virtual scene allows an automated embedding of raytraced 3D objects. The results show that these methods can be used in the field of environmental planning, civil engineering and other applications where terrain visualization is required.     

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.     

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.     

An integrated approach to geometric precision processing of spaceborne high-resolution sensors

The plantmetric errors due to terrain relief and atmospheric refraction must be considered when high geometric resolution sensors and off-nadir viewing angles are used. This paper presents an approach to correct these errors using an integrated procedure that takes into account geometric and radiometric effects, connected to simulations of future remote-sensing systems or precision data processing. A diagram shows the relation between the root mean square error of the digital elevation model necessary to correct the terrain relief effect and the achievable scale of the output image map. The procedure is currently applied to the SPOT simulation on the Basilicata test site in southern Italy. A short example is given to analyse the geometric errors involved.     

Stereo-mapping with SPOT-P and ERS-1 SAR images

This paper reports on some aspects of using mixed radar and visible sensors to generate stereo-pairs that are suitable for stereo-mapping planimetric and elevation features. By choosing compromises to reduce geometric and radiometric disparities, the brain is able to perceive depth and to combine the complementary aspects of the radiometries from a VIR/SAR stereo-pair. Quantitative results of mapping and feature extraction from opposite and same-side ERS-SAR and SPOT-P stereo images are presented. In planimetry, accuracy of about 30m is obtained. Such accuracy is dependent on the stereo-pair, the stereo viewability, the image content and the feature definition. In altimetry, 20-m accuracies are obtained for both stereo-pairs. The strongest stereo geometry does not explicitly lead to better results, because with these mixed SAR/VIR stereo-pairs the major contributor to the elevation parallax is the SAR geometry. Finally, from the stereo-fusion of these two ERS-SAR/SPOT-P pairs, the radiometry of the SPOT-P images mainly contributes to the determination of the planimetric features with the quality of its image content; while the geometry of the ERS-SAR image mainly contributes to the determination of the elevation with its high sensitivity to the terrain relief.     

基于匹配与平差的景象镶嵌方法

在概括介绍消附相邻景象辐射差异常用算法的基础上,为有效消除相邻景象间几何位置的差异,提出了一种将影象匹配与平差理论相结合的影象镶嵌新算法,该方法是在镶嵌影象的重叠部分进行基于特征的影象匹配,即首先获取一序列同名点,且这些同名点的匹配精度在一个象元以内;然后用正形多项式模拟这些同名点间的几何位置差异,再按最小二乘法原理对右边影象进行平差改正,以实现两影象空间位置上的无缝连接。实验结果表明,庐镶嵌方法具有良好的效果。     

基于高亮特征匹配的双视向SAR图像建筑物高度提取

由于城区场景的复杂性和SAR成像几何畸变的影响,基于单幅SAR图像的建筑物高度提取常常存在很大困难。针对这一问题,利用建筑物目标SAR成像形成的叠掩、二次散射、较强单次散射等散射机制对应的高亮特征非常典型,并且对方向性敏感的特点,提出了一种基于双视向SAR图像高亮特征与几何模型匹配的建筑物高度提取方法。首先分析了建筑物目标的SAR图像散射特征及对雷达视向的敏感性,然后构造了建筑物目标在双视向SAR图像上高亮特征几何模型,然后基于灰度均值、灰度概率分布、边界信息定义匹配函数,并利用多种群遗传算法进行优化求解,最终得到建筑物目标的高度信息。基于模拟和机载SAR图像的试验表明该方法的建筑物高度平均反演误差小于1m,可以有效提高建筑物高度反演的精度。     

An automatic geometric precision correction system based on hierarchical registration for HJ-1 A/B CCD images

On 6 September 2008, two optical satellites, HJ-1 A and B (HJ-1 A/B), were successfully launched from China. However, the system geometric correction products of the HJ-1 A/B charge-coupled device (HJ-1 images) have low geometric precision and need to be corrected. The HJ-1 images have a large aspect angle, a wide swath width, and a large image size. Furthermore, the local geometric distortions are too complex in one scene. Given these characteristics of HJ-1 images, geometric correction is still a challenging work. This article proposes an automatic geometric precision correction system (GPCS) based on the automatic registration between HJ-1 images and Landsat Thematic Mapper images. First, the coarse image matching method based on geometric-restricted scale-invariant feature transform (SIFT) is used to determine the coarse global transformation between the HJ-1 image and the reference image. Second, inspired by the hierarchical method of non-rigid registration for medical images, a hierarchical image matching approach is proposed based on the combination of SIFT feature points and template matching. This approach decomposes a matching problem of a whole image into numerous matching problems of image blocks and can overcome the impact of local distortions in HJ-1 images. Hierarchical random sample consensus (RANSAC) based on digital elevation model (H-RANSAC) is used to remove incorrect control points. Third, an HJ-1 image is rectified using a triangulated irregular network. Finally, the automatic evaluation method based on automatic image matching between the corrected HJ-1 image and the reference image is adopted to evaluate the geometric precision. On the one hand, experiments on eight HJ-1 images demonstrate the efficiency and accuracy of the different steps of GPCS. On the other hand, experiments on 1000 HJ-1 images also demonstrated the robustness, accuracy, and suitability for batch processing.     

基于外部DEM的InSAR图像配准方法研究

雷达图像的配准是进行雷达干涉测量(SAR Interferometry, InSAR)处理的关键,为了保证干涉相位图或形变相位图反映真实地面特性,需要雷达图像之间亚像元级精度的配准。首先综述了已有的基于外部DEM的InSAR图像配准方法的思路及其不足之处,并提出了一种全新的思路:以图像之间的相干性作为目标函数,利用搜索的方法实现了雷达成像方位向和距离向的最优时间常数的估计,从而实现雷达图像之间亚像元级配准;还进一步推导了数字高程模型(Digital Elevation Model, DEM)的误差对算法精度影响的一个更加严密的表示。结论表明,在利用精确轨道数据的情况下,美国航天飞机测地计划SRTM获得的地形数据的精度可以满足精确雷达图像配准的要求。结果表明,利用基于外部DEM算法配准雷达图像在山区和大的时间基线情况下要优于常规相干多项式配准方法,理论上可以达到百分之一个像素的配准精度。     

An experimental evaluation of non‐rigid registration techniques on Quickbird satellite imagery

In remote sensing, because of the wide diversity of image characteristics (size, spatial and radiometric resolution, terrain relief, observation poses, etc.), image registration methods that work well on certain satellite images may not produce acceptable results for others, requiring more powerful techniques. A variety of registration techniques that account for images with non‐rigid geometric deformations have been proposed, including piecewise (linear or cubic) functions, weighted mean functions, radial basis functions, B‐spline functions, etc. This paper compares three of them: polynomial, piecewise‐linear and thin‐plate‐spline functions, and analyses their performance under a variety of factors: off‐nadir viewing, terrain relief, density of control points, and 3D geometric correction. Our comparison applies on panchromatic QuickBird imagery, both ortho‐ready (as provided by DigitalGlobe) and orthorectified, acquired on different dates, from different observation attitudes, and sensing different land covers: urban area, high‐relief terrain, and a combination of both.     

Automatic detection of oil spills from SAR images

A probabilistic method has been developed that distinguishes oil spills from other similar sea surface features in synthetic aperture radar (SAR) images. It considers both the radiometric and the geometric characteristics of the areas being tested. In order to minimize the operator intervention, it adopts automatic selection criteria to extract the potentially polluted areas from the images. The method has an a priori percentage of correct classification higher than 90% on the training dataset; the performance is confirmed on a different dataset of verified slicks. Some analyses have been conducted using images with different radiometric and geometric resolutions to test its suitability with SAR images different from European Remote Sensing (ERS) satellite ones. The system and its ability to detect and classify oil and non‐oil surface features are described. Starting from a set of verified oil spills detected offshore and over the coastline, the ability of SAR to reveal oil spills is tested by analysing wind intensity, deduced from the image itself, and the distance from the coast.     

全极化合成孔径雷达影像地形纠正及其在雪冰制图中的应用

针对合成孔径雷达（SAR）影像由于地形起伏引起的图像畸变问题,文章提出了基于相干矩阵的全极化SAR影像地形纠正算法,并运用于雪冰制图。该方法首先采用距离多普勒模型建立SAR成像几何模型;然后利用全极化Cloude特征分解方法对全极化SAR图像进行融合,将融合后的SAR图像与模拟图像进行配准提高SAR影像几何定位精度;最后利用投影面积归一化和极化方位角移动补偿技术对地形引起的辐射畸变进行纠正。采用中国长江源区南部唐古拉山中段冬克玛底冰川区域的C波段Radarsat-2全极化SAR数据进行验证,配准模拟SAR和原始SAR影像的控制点方位向和距离向的均方根误差（RMSE）分别为7.765和14.586个像素;经过地形纠正后的地物分类精度达80%以上。结果表明：（1）该方法能够有效消除SAR影像中几何和辐射畸变的影响;（2）地形纠正后的SAR数据在雪冰制图中具有可行性。     

SAR imaging simulation for an inhomogeneous undulated lunar surface based on triangulated irregular network

Based on the statistics of the lunar cratered terrain, e.g., population, dimension and shape of craters, the terrain feature of cratered lunar surface is numerically generated. According to the inhomogeneous distribution of the lunar surface slope, the triangulated irregular network (TIN) is employed to make the digital elevation of lunar surface model. The Kirchhoff approximation of surface scattering is then applied to simulation of lunar surface scattering. The synthetic aperture radar (SAR) image for comprehensive cratered lunar surface is numerically generated using back projection (BP) algorithm of SAR imaging. Making use of the digital elevation and Clementine UVVIS data at Apollo 15 landing site as the ground truth, an SAR image at Apollo 15 landing site is simulated. The image simulation is verified using real SAR image and echoes statistics. Supported by the National Matural Science Foundation of China (Grant No. 40637033)     

机载AISA Eagle Ⅱ高光谱数据处理——以额济纳旗试验区为例

机载AISA EagleⅡ传感器为"黑河综合遥感联合试验(HiWATER)"额济纳旗试验区提供航空高光谱影像。介绍了高光谱原始数据的辐射定标、几何校正、大气校正等预处理过程。根据研究区地形差异以及数据使用目的的多样性,几何校正中可选择是否加高精度DEM产品,大气校正的选择策略可分为平坦地形无DEM的大气校正和起伏地形添加DEM大气校正。本试验数据采用加载高精度DEM的几何校正和平坦地形大气校正方法,经过预处理后的高光谱数据产品,其地理坐标与高分辨率的CCD影像对比,地理位置信息较为准确;与实测地物光谱对比,影像光谱能较好地体现地物光谱的特性,数据可用作定量遥感进一步的研究。     

An approach based on hybrid genetic algorithm applied to image denoising problem

An approach based on hybrid genetic algorithm (HGA) is proposed for image denoising. In this problem, a digital image corrupted by a noise level must be recovered without losing important features such as edges, corners and texture. The HGA introduces a combination of genetic algorithm (GA) with image denoising methods. During the evolutionary process, this approach applies some state-of-the-art denoising methods and filtering techniques, respectively, as local search and mutation operators. A set of digital images, commonly used by the scientific community as benchmark, is contaminated by different levels of additive Gaussian noise. Another set composed of some Satellite Aperture Radar (SAR) images, corrupted with a multiplicative speckle noise, is also used during the tests. First, the computational tests evaluate several alternative designs from the proposed HGA. Next, our approach is compared against literature methods on the two mentioned sets of images. The HGA performance is competitive for the majority of the reported results, outperforming several state-of-the-art methods for images with high levels of noise.     

Reduction of atmospheric and topographic effect on Landsat TM data for forest classification

The incident radiance in forested areas with rugged terrain varies greatly with the changes in solar elevation and azimuth, slope and aspect of the terrain, and the relative position of trees. The geotropic nature must be considered in the course of topographic correction. The Sun‐Canopy‐Sensor (SCS) model is introduced to substitute the cosine correction in a physical model. We used an atmospheric simulation code, MODTRAN, and a digital elevation model (DEM) to calculate the path radiance, downwards diffuse radiance and two‐way transmittance of direct and diffuse light at different altitudes. Based on the atmospheric parameters derived above and the Lambertian assumption, surface reflectance in a forested area was retrieved from Landsat Thematic Mapper (TM) imagery using a revised physical model. Meanwhile, a smoothed DEM was used to assess the effect of noise on the DEM and misregistration between the DEM and the satellite imagery. Correlation analysis, spectral comparison between sunlit and shaded slopes and a support vector machine (SVM) classification were performed to assess the effect of the revised radiometric correction algorithm. Results indicate that the revised physical model with smoothed DEM is more adequate for forested terrain and more consistent spectra for similar vegetation under different illuminations can be obtained. Finally, higher classification accuracy of forested land can be achieved with the revised correction algorithm compared with the SCS correction and the original physical correction model.     

Single versus stereo ERS-1 SAR imagery for planimetric features extraction

This Letter compares two conventional methods for the extraction of planimetric features: the monoscopic method, using an image and a digital elevation model to generate an ortho-image; and the stereoscopic method, using two images for the three-dimensional reconstruction of the stereoscopic model of the terrain.Feature extraction then occurs in mono or stereoscopic viewing,depending on the method used. When compared with the topographic data, accuracies of the lake shoreline extraction from ERS-1 SAR images show 22m versus 17 m root mean square accuracies with 66 per cent confidence for the monoscopic and stereoscopic methods, respectively. More consistency is also achieved with the stereoscopic method.     

Terrain topographic inversion using single-pass polarimetric SAR image data

1IntroductionFullypolarimetricSARimagerytechnologyisoneofthemostimportantadvance-mentsforspace-borneremotesensing.Ithasbeenextensivelyappliedtoterrainsurfaceclassification.The22-D(Dimensional)complexscatteringamplitudefunctionsFpq(p,q=v,h),and44-DrealMuellermatrixMij(i,j=1,…,4)canbemeasured[1].Co-polarizedorcross-polarizedbackscatteringsignatureisthefunctionoftheincidencewavewiththeellipticityanglecandorientationangley.Recently,twoflightsofpo-larimetricSARimagedatahavebeenutilizedtogene…     

Image correction for radiometric effects in remote sensing

A general classification of radiometric correction methodologies yields new insights into related procedures as they are implemented typically on image analysis systems. Incorrect results can be obtained from the inappropriate application of different types of corrections related to physical phenomena which give rise to radiometric distortions in a scene. The major types of radiometric correction are reviewed as they apply to digital images acquired by satellite sensors in the visible and infrared portions of the spectrum.