Mapping trees in high resolution imagery across large areas using locally variable thresholds guided by medium resolution tree maps

Large area tree maps, important for environmental monitoring and natural resource management, are often based on medium resolution satellite imagery. These data have difficulty in detecting trees in fragmented woodlands, and have significant omission errors in modified agricultural areas. High resolution imagery can better detect these trees, however, as most high resolution imagery is not normalised it is difficult to automate a tree classification method over large areas. The method developed here used an existing medium resolution map derived from either Landsat or SPOT5 satellite imagery to guide the classification of the high resolution imagery. It selected a spatially-variable threshold on the green band, calculated based on the spatially-variable percentage of trees in the existing map of tree cover. The green band proved more consistent at classifying trees across different images than several common band combinations. The method was tested on 0.5 m resolution imagery from airborne digital sensor (ADS) imagery across New South Wales (NSW), Australia using both Landsat and SPOT5 derived tree maps to guide the threshold selection. Accuracy was assessed across 6 large image mosaics revealing a more accurate result when the more accurate tree map from SPOT5 imagery was used. The resulting maps achieved an overall accuracy with 95% confidence intervals of 93% (90–95%), while the overall accuracy of the previous SPOT5 tree map was 87% (86–89%). The method reduced omission errors by mapping more scattered trees, although it did increase commission errors caused by dark pixels from water, building shadows, topographic shadows, and some soils and crops. The method allows trees to be automatically mapped at 5 m resolution from high resolution imagery, provided a medium resolution tree map already exists.     

利用SPOT影像制作立体正射影像图的研究

本文论述了利用ＳＰＯＴ影像制作立体正射影像图的基本原理。阐述了利用数字微分纠正方法制作正射影像图和视差匹配影像图的基本方法。最后利用我国西南高山地区１ＡＰ级ＳＰＯＴ影像制作了一幅１：１００ ０００比例尺的立体正射影像图。     

Assessment of SPOT 5 and QuickBird remotely sensed imagery for mapping tree cover in savannas

The relative abundance and distribution of trees in savannas has important implications for ecosystem function. High spatial resolution satellite sensors, including QuickBird and IKONOS, have been successfully used to map tree cover patterns in savannas. SPOT 5, with a 2.5 m panchromatic band and 10 m multispectral bands, represents a relatively coarse resolution sensor within this context, but has the advantage of being relatively inexpensive and more widely available. This study evaluates the performance of NDVI threshold and object based image analysis techniques for mapping tree canopies from QuickBird and SPOT 5 imagery in two savanna systems in southern Africa. High thematic mapping accuracies were obtained with the QuickBird imagery, independent of mapping technique. Geometric properties of the mapping indicated that the NDVI threshold produced smaller patch sizes, but that overall patch size distributions were similar. Tree canopy mapping using SPOT 5 imagery and an NDVI threshold approach performed poorly, however acceptable thematic accuracies were obtained from the object based image analysis. Although patch sizes were generally larger than those mapped from the QuickBird image data, patch size distributions mapped with object based image analysis of SPOT 5 have a similar form to the QuickBird mapping. This indicates that SPOT 5 imagery is suitable for regional studies of tree canopy cover patterns.     

PHOTOGRAMMETRIC DEVELOPMENTS IN THE ORDNANCE SURVEY IN 1990

The author, a research and development manager at Ordnance Survey, reviews current developments in photogrammetry including the automatic correlation of image points for aerial triangulation, digital photogrammetric map revision, mapping from SPOT imagery and progress in aerial photography.     

Regional mapping of the South Armorican shear zone (Brittany, France) using remotely sensed SPOT imagery

The South Armorican shear zone is one of the major occurrences of Variscan basement in Europe. The objectives of the study were to compile a lineament and a structural map from remotely sensed SPOT imagery. Transparent color films, enhanced by high-pass filtering and by stretching color composites, and spatial filtered images were analysed. The major structure mapped corresponds to a dextral transcurrent shear belt in which C and S axes have been described. Late Paleozoic and Tertiary fracturations truncate these structures. The localisation, extension and geometry of granite domes were also precised. Lastly, this study provides a good example of structural interpretation of a moderate-relief terrain using high-resolution SPOT imagery.     

SPOT影象的解析摄影测量处理

SPOT立体影象具有良好的基高比和空间分辨率,可以利用解析摄影测量仪器对之进行精确而有效的处理,以求解外方位元素,测制或修测地形图,获取数字高程模型以及制作正射影象。本文分析了SPOT影象的几何特性,建立了SPOT立体象对求解的数学模型。利用作者研制的SPOT影象光束法平差程序、C-100解析测图仪上SPOT象对测图软件和在OR-1正射投影仪上制作SPOT正射影象的相应软件,对法国马赛地区的一对SPOT立体象对进行了试验,获得了满意的结果。     

单侧控制条件下SPOT5 HRG影像的定向试验

高分辨率卫星影像已经成为获取地理信息的重要数据源,而其定向是一项关键技术。本文利用单侧不同数量及分布的控制点对SPOT5 HRG影像进行了定向试验,探讨了在单侧控制条件下SPOT5 HRG影像的定向精度情况,为地面控制点获取较困难地区的影像定向提供了一条参考途径。     

稀少控制条件下的SPOT 5 HRS影像定向试验

通过生产试验,探讨了不同控制点数量及分布下的SPOT 5 HRS影像的定向精度问题,分析了稀少控制点定向后SPOT 5 HRS影像的误差分布情况,为SPOT 5 HRS影像在外业控制点获取困难地区的应用提供了可行方法。     

SPOT DATA EVALUATION AND USE AT INSTITUT GÉOGRAPHIQUE NATIONAL, FRANCE

Since the launch of SPOT, Institut Géographique National, France has carried out several investigations concerned with in-flight evaluation, research operations and the setting up of production flowlines. The aims of assistance to data bank establishment, revision of existing maps and image map and thematic map production have now been achieved for the most part. Some procedures are already operational, including image product making, photogrammetry on SPOT images, classifications on image processing systems, manual information retrieval and image map production. Moreover, various research operations are virtually complete, including automatic correlation, composite processes between aerial photographs and SPOT images, quite promising mathematical morphology associated with expert systems for retrieving linear or complex textured (built up area) elements, and manual cartography on image processing system. These results confirm the great benefits of SPOT system capabilities and the characteristics of flexibility, accuracy and reliability. The Photogrammetric Society and the Remote Sensing Society held a one-day symposium at Burlington House, London on 11th November, 1987. The SPOT (Système Probatoire d'observation de la Terre) satellite had then been operational for 18 months and many organisations had been working with the data. This symposium reviewed the operation of the satellite and studies which had been carried out for mapping and for thematic applications. Six of the symposium papers are published here. It is expected that other papers from the symposium will be published in the International Journal of Remote Sensing.     

Bathymetric Estimation Using MERIS Images in Coastal Sea Waters

Bathymetric estimation using remote sensing images has previously been applied to high spatial resolution imagery such as CASI, Ikonos, or SPOT but not on medium spatial resolution images (i.e., MERIS). This choice can be justified when there is a need to map the bathymetry on large areas. In this letter, we present the results of the bathymetry estimation over a large known area, the Gulf of Lion (France), expanding over 270times180 km     

基于SPOT5遥感影像的湿地资源调查方法研究

通过利用SPOT5遥感影像对湿地资源调查方法的实验研究,探讨了遥感影像的融合方法,选取适合湿地资源调查的数据融合和重采样方法,并解译融合后的遥感数据。从而获取湿地研究区的分类数据。     

GROUND CONTROL DETERMINATION FOR REGISTRATION OF SATELLITE IMAGERY USING DIGITAL MAP DATA

Work is reported on the production of terrain elevation data from SPOT imagery. An important step in this process is determination of exterior orientation parameters for the images. Although an initial estimate is available in the SPOT header, refinements are required based on plan and height data. These are generally derived from photogrammetric measurements (or sources such as global positioning satellite systems), but accurate manual determination is time consuming. This paper reports an alternative approach by investigating the use of existing map data (located on the earth's surface and in a known projection) to find corresponding “ground control points” in both map and image. Available maps may be in digital or paper form depending on the state of development of mapping in the part of the world being studied. The last revision date and the cartographic generalisation employed will also effect the fidelity of the final result. Practical semi-automatic techniques for determining the height of ground control points from existing map data are described, including multiple profiles through digitised contour data, a commercial terrain modelling package based on Delaunay triangulation and the use of triangulation points on prominent features. Comparisons between the methods are made and results obtained are compared with Institut Géographique National datasets and photogrammetric measurements. Methods for fully automating not only the height determination but also the location of ground control features within a map database are discussed. Map and image registration is described and illustrated using Laser-Scan's Rover software. Interactive and automated methods of registration are discussed.     

EMPIRICAL MODELS FOR ATTITUDE VARIABILITY OF THE SPOT I SATELLITE

Longer sequences of attitude data for SPOT 1 were constructed by concatenation of the attitude information in several consecutive scenes in selected orbits. The attitude time series were used to estimate models for the attitude variogram functions. Explicit expressions for these models are given, which can be used in multi-scene adjustment of SPOT imagery.     

PASS PROCESSING AND EXTRAPOLATION OF SPOT IMAGE GEOMETRY

A mathematical model for pass processing of SPOT imagery is formulated. It is based on the fact that during one pass, the image data stream from each of the instruments in SPOT forms one single very long image. The geometry of this extended image can thus be rectified with as few control points as for only one scene if orbital constraints and attitude measurements are properly taken into consideration. SPOT imagery is, however, not available as this single long image, but only sectioned into scenes. This creates problems which are accounted for in the solution. The possibility of gaps in the sequence of scenes is also taken into consideration. Extrapolation over gaps is of special interest and, by investigating attitude variability, it is shown that extrapolation is successful over multiple scene gaps which is also verified in a real data test.     

岭-压缩组合估计在线阵推扫式影像外定向中的应用

针对线阵推扫式影像外定向中存在的法方程病态问题,提出了采用岭压缩组合估计进行解算,能提高定向精度,并分析了该算法的优点和应用方法。实验证明,该算法性能优异,精度很高。     

SPOT 5卫星影像测绘能力分析

HRS同轨立体影像获取能力是SPOT5卫星最突出的一个关于测绘制图的新特性,它确定了SPOT5卫星在测绘中的重要应用前景。本文从SPOT5HRS的立体成像方式,SPOTImage公司最新推出的Reference3D产品及陕西宝鸡地区的HRS立体影像测量试验等方面对SPOT5HRS影像测绘能力进行了分析和评价,说明了SPOT5卫星影像测绘将是解决我国西部困难地区基础测绘的一种重要手段。     

Field-based sub-boundary extraction from remote sensing imagery using perceptual grouping

This study presents an approach for the automatic extraction of dynamic sub-boundaries within existing agricultural fields from remote sensing imagery using perceptual grouping. We define sub-boundaries as boundaries, where a change in crop type takes a place within the fixed geometry of an agricultural field. To perform field-based processing and analysis operations, the field boundary data and satellite imagery are integrated. The edge pixels are detected using the Canny edge detector. The edge pixels are then analyzed to find the connected edge chains and from these chains the line segments are detected using the graph-based vectorization method. The spurious line segments are eliminated through a line simplification process. The perceptual grouping of the line segments is employed for detecting sub-boundaries and constructing sub-fields within the fixed geometry of agricultural fields. Our strategy for perceptual grouping involves the Gestalt laws of proximity, continuation, symmetry and closure. The processing and analysis operations are carried out on field-by-field basis. For each field, the geometries of sub-boundaries are determined through analyzing the line segments that fall within the field and the extracted sub-boundaries are integrated with the fixed geometry of the field.The experimental validation of the approach was carried out on the SPOT4 multispectral (XS) and SPOT5 XS images that cover an agricultural area located in the north-west section of Turkey. The overall matching percentages between the reference data and the automatically extracted sub-boundaries were computed to be 82.6% and 76.2% for the SPOT5 and SPOT4 images respectively. The higher matching percentage of the SPOT5 image is due to the fact that some of the boundaries present in the SPOT5 image were not detected in the coarser resolution SPOT4 image. For the SPOT5 image, of the total 292 fields processed, 177 showed a total agreement between the detected segments and the reference data. For the SPOT4 image, 154 fields showed a total agreement between the detected segments and the reference data.     

Comparing Fire Severity Models from Post-Fire and Pre/Post-Fire Differenced Imagery

Wildland fires are common in rangelands worldwide. The potential for high-severity fires to affect long-term changes in rangelands is considerable, and for this reason assessing fire severity shortly after the fire is critical. Such assessments are typically carried out following Burned Area Emergency Response teams or similar protocols. These data can then be used by land managers to plan remediation and future land uses. To complement these procedures and explore fire severity modeling of sagebrush steppe rangelands, we compared models developed using (1) post-fire imagery only with (2) differenced imagery (pre-fire minus post-fire imagery). All models were developed from Classification Tree Analysis (CTA) techniques using Satellite Pour l'Observation de la Terre 5 (SPOT 5) imagery and Shuttle Radar Topography Mission (SRTM) elevation data. The results indicate that both techniques produced similar fire severity models (model agreement = 98.5%) and that little improvement in overall accuracy was gained by using differenced imagery (0.5%). We suggest the use of CTA models developed using only the post-fire imagery. The analyses and techniques described in this paper provide land managers with tools to better justify their recommendations and decisions following wildland fires in sagebrush steppe ecosystems and provide remote sensing scientists with information that will potentially improve future modeling efforts.     

Urban land use mapping and zoning of Bombay Metropolitan Region using remote sensing data

Bombay Metropolitan Region covering an area of about 4,360 sq. km. was selected for urban land use studies and for urban land use zoning. Urban land use mapping was carried out using SPOT multispectral linear array imagery on 1∶25,000 scale employing visual analysis tehcniques. Fifteen maps were prepared depicting the spatial distribution of various urban classes in the Greater Bombay and New Bombay regions. Sixteen urban land use maps were also prepared using Landsat TM data showing the distribution of land use pattern on 1∶50,000 scale for the entire metropolitan region. Urban land use zoning was carried out based upon suitability index on 1∶250,000 scale. This map provides information on the areas to be used for construction and areas to be kept under green belt in the metropolitan region. This study is a joint venture of Space Applications Centre with Bombay Metropolitan Development authority.     

Landcover Classification in the Taieri River Catchment,New Zealand: A Focus on the Riparian Zone

Abstract

Riparian vegetation has a fundamental influence on the biological, chemical and physical nature of rivers. The quantification of riparian landcover is now recognised as being essential to the holistic study of the ecosystem characteristics of rivers. Medium resolution satellite imagery is now commonly used as an efficient and cost effective method for mapping vegetation cover; however such data often lack the resolution to provide accurate information about vegetation cover within riparian corridors. To assess this, we measure the accuracy of SPOT multispectral satellite imagery for classification of riparian vegetation along the Taieri River in New Zealand. In this paper, we discuss different sampling strategies for the classification of riparian zones. We conclude that SPOT multispectral imagery requires considerable interpretative analysis before being adequate to produce sufficiently detailed maps of riparian vegetation required for use in stream ecological research.