Proceedings of the Symposium on Global and Environmental Monitoring: Proceedings of the Symposium on Global and Environmental Monitoring

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Persistent identifier:: 856665355

Title:: Proceedings of the Symposium on Global and Environmental Monitoring

Sub title:: techniques and impacts ; September 17 - 21, 1990, Victoria Conference Centre, Victoria, British Columbia, Canada

Year of publication:: 1990

Place of publication:: Victoria, BC

Publisher of the original:: [Verlag nicht ermittelbar]

Identifier (digital):: 856665355

Language:: English

Document type:: Multivolume work

Volume

Persistent identifier:: 856669164

Title:: Proceedings of the Symposium on Global and Environmental Monitoring

Sub title:: techniques and impacts; September 17 - 21, 1990, Victoria Conference Centre, Victoria, British Columbia, Canada

Scope:: XIV, 912 Seiten

Year of publication:: 1990

Place of publication:: Victoria, BC

Publisher of the original:: [Verlag nicht ermittelbar]

Identifier (digital):: 856669164

Illustration:: Illustrationen, Diagramme, Karten

Signature of the source:: ZS 312(28,7,1)

Language:: English

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Editor:: International Society for Photogrammetry and Remote Sensing, Commission of Photographic and Remote Sensing Data

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2016

Document type:: Volume

Collection:: Earth sciences

Chapter

Title:: [FA-1 TOPOGRAPHIC ANALYSIS]

Document type:: Multivolume work

Structure type:: Chapter

Chapter

Title:: VISIBILITY AND SHADOW STATE OF STEEP SLOPES IN STEREO-OBSERVATION OF SIDE-LOOK SPOT IMAGERY. JAN J. NOSSIN

Document type:: Multivolume work

Structure type:: Chapter

815 INTRODUCTION In this paper, we analyze the visibility and shadow state of steep slopes in sidelook SPOT imagery. The presence or absence of a slope can, practically, only be determined in ster eo-imagery; throughout this paper therefore, we presume the context of stereo observations. We shall consider the slope direction as the horizontal projection of a line normal to the contours, viewed in the down-slope direction. The satellite flies in the southward direction on the daytime overpass. The rightlooking position therefore looks to the west of the satellite, the leftlooking position, to the east. Stereo imagery is obtained if the same scene is imaged by the satellite twice from different angles. For each image of a stereopair, the user has to know the lookangle and direction, and the date of acquisition of the data. This informa tion is routinely supplied in the leader file of the CCT's. Stereopairs in any case do not show simultaneous situations in both images. We shall use the term 'eastward' for slope expositions eastward of the flight path direction; similarly, westward will be used to indicate expositions west ward of the flight direction. The look-angle of the satellite (i.e. the angle of the mirror with the vertical) differs from the incidence angle, which is the angle that the line of view from the satellite makes with the surface normal at the scene centre; this difference is due to the earth's curvature. We shall call the complement of the incidence angle, the viewangle. In side-look SPOT imagery, slopes steeper than the viewangle, exposed in the lookdirection, are not visible to the satellite, and hence, not imaged. Slopes with a westerly exposure in the direction (sun azimuth + 180°) steeper than the sun elevation angle, are in shadow. Slopes with a slope angle less than the sun elevation and exposed in the same direction, are sunlit. On left-look (i.e: eastlook) images, slopes exposed in the lookdirection of the satellite, i.e. slopes with an eastward exposure component, are generally all sunlit, but slopes with a slope angle > viewangle are not visible to the satel lite. In west-look Spot imagery, slopes exposed in westerly directions, different from the lookdirection of the satellite or the direction (sun azimuth + 180°), may be or not be imaged, while sunlit or in shadow, depending on slope angle, exposure, sun azimuth, and sun elevation. The combined effect of sunlit status for certain slopes, and non-visibility of shadowed slopes, may give rise to marked absence of contrast in west-look ima gery of steep terrain with steep westfacing slopes. This effect is especially noted in strong west-look imagery. It was first noted and described for images of steep karstified terrain in Turkey (Nossin, 1989) and analyzed by the same author,(1990). Images from several areas are shown to serve as illustrations of this effect.

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