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Terrain Analysis from Digital Patterns in Geomorphometry and Landsat MSS Spectral Response Terrain Analysis from Digital Patterns in Geomorphometry and Landsat MSS Spectral Response Steven E. Franklin Department of Geography, Memorial University of Newfoundland, St. John's, Newfoundland AlB 3X9, Canada ABSTRACT: Digital Landsat multispectral images are used with elevation model variables in high relief terrain analysis. An integrated terrain map from conventional photomorphic methods (based on aerial photointerpretation) is compared with the results of digital processing methods. The objective is to show that there will be a reasonable correspondence between the analogue and digital mappings, and that digital data and methods offer significant advantages in terms of survey reliability, accuracy, and repeatability. Digital patterns in spectral response and geomorphometry are shown to capture those attributes of the surface necessary for classification of landscape units. Classification of the MSS digital patterns showed up to 46 percent agreement with photomorphic survey methods. Agreement rose up to 75 percent as the MSS data were augmented with the geomorphometric patterns. Maps produced using this enhanced discrimination technique are 70 percent accurate when the classes are weighted by area and compared to the photointerpretation on a pixel-by-pixel basis at field-checked test areas. Greater overall interpretation accuracy might have been obtained with more precise digital class description, greater rigor in the conventional survey, or both. INTRODUCTION mine class structures and supervise the classification. The resulting digital maps are used in an assessment of the corre­ ANDSCAPE UNITS are composed of recurring patterns in veg­ spondence between analog and digital interpretations of terrain Letation, soils, landform, and lithology. These units have been phenomena generalized into the nine landscape classes of in­ used in terrain analysis based on metric aerial photointerpre­ terest. tation and field observation for over 30 years in many parts of the world (Christian and Stewart, 1968; Townshend, 1981; THE STUDY AREA Franklin, 1985). These integrated, or landscape, surveys have The study area encompasses an area of 100 square kilometres sometimes been criticized (Hutchinson, 1978; Story et ai., 1976) within the Ruby Range near Aishihik Lake in southwestern as a consequence of the lack of objectivity and repeatability of Yukon Territory (Figure 1). This range is one of a series of gran­ survey results. diorite-schist plateaux. During the last (Wisconsin) ice maxi­ Recently, digital data from sensors on platforms such as mum, lobes extended northward from the St. Elias Ice Sheet Landsat have been used to increase landscape survey reliability. along valleys now occupied by Aishihik Lake and Sekulmun The research of Robinove (1979) and Hutchinson (1978) in arid Lake. Moraine deposits dominate the surficial geology, and lands survey was based on the hypothesis that mapping inte­ postglacial alluvial and lacustrine deposits are evident in flood­ grated characteristics of land can be done by computer analysis plains and fans. Because the till covering varies considerably in of multispectral images. Those studies built on earlier discus­ texture and thickness, bedrock and volcanic outcropping is sion and research in the landscape approach (Mabbutt, 1968; common. Several such features are visible in the orthophoto­ Story et ai., 1976). They emphasized the problems in subjectivity graph shown in Figure 2. of analog image interpretations, survey repeatability and ac­ The region has a continental and semi-arid climate with mean curacy, and the selection of descriptor variables, such as Land­ daily temperatures in the past three decades of - 24.3°C Gan­ sat MSS spectral response patterns, for use in representing uary) and + 12.1°C Guly). A mean annual precipitation of 248.3 landscape criteria. These are continuing problems in terrain mm was recorded with the greatest amount occuring in sum­ analysis and classification. mer. On north facing slopes in the Ruby Range, perennial snow The research described here was designed to address some is common, though not within the confines of the present study of these methodological problems in the analysis of a subarctic, site. alpine region in Northern Canada. The main hypothesis is that, During tWQ field seasons with an interdisciplinary field team, in this high relief environment, the discrimination and mapping strong structural control and altitudinal zonation on the growth of landscape units can be done accurately through the classifi­ of vegetation species were noted (Franklin, 1985). In the valleys cation of multispectral images with elevation model variables. the dominant vegetation is white spruce. With increasing ele­ To test this research hypothesis, digital Landsat MSS data were vation, a mixed woodland cover containing deciduous species acquired for 1 August 1978. The image has a sun elevation of is present. A patchy upland shrub cover is found up to ap­ 43 degrees and sun azimuth of 154 degrees, and is cloudfree. proximately 1500 metres elevation; and above, a bryoid mat An elevation model was generated from August 1979 metric consisting of lichens and mosses is found in conjunction with aerial photographs (scale 1:60000) on the Gestalt Photomapper tundra and alpine barrens. The elevation ranges from 812 to II (an image correlator). The variables extracted from this model 1755 metres above sea level. Low gradient slopes extend the conform to the general system of geomorphometry (Evans, 1972) width of the major river valleys. In general, as elevation in­ and provide a quantitative basis for topographic descriptions of creases, slopes become steeper and more variable (Figure 3). terrain surfaces and landforms. The digital analysis of these data is described in two stages. THE INTEGRATED APPROACH The first stage, correlation analysis, is used to document the nature of the relationships between spectral response patterns In the integrated approach to terrain classification, landscape and surface elevation and geometry. The second stage is a dis­ units are described as areas having unique combination of to­ criminant analysis in which we use field observations to deter- pography, soils, vegetation, and lithology. Many surveys using PHOTOGRAMMETRIC ENGINEERING AND REMOTE SENSING, 0099-1112/87/5301-59$02.25/0 Vol. 53, No. 1, January 1987, pp. 59--65. ©1987 American Society for Photogrammetry and Remote Sensing 60 PHOTOGRAMMETRlC ENGINEERING & REMOTE SENSING, 1987 Beaufort Sea (using the parametric criteria) of the given (analog) classification i o scheme in training areas has been made, the decision rule is i applied to areas where the classes are known, but where little i i is known of the terrain attributes themselves. The power of the i digital method is twofold: (1) the limitation of analog subjectiv­ i i ity explicitly in training areas; and (2) the use of a repeatable, i consistent extension to other areas. i Id Crow Other studies have illustrated the suitability of Landsat MSS i data in classification of certain terrain types according to the i i --'\ landscape approach (Robinove, 1979, 1981). Spectral response :ig patterns are surrogates for some of the attributes (e.g., vege­ .:J/~ ') ~t tation cover, soils) that are combined to describe landscape units i \ i V·v:; on the ground and in aerial photographs. However, in high i relief, topographic expression (landform) can be a critical com­ i ) ponent in classification (Hutchinson, 1978; Franklin and Le­ ~" ( Drew, 1984; Christian and Stewart, 1968). Such descriptions are ! Clinton Crttk (\. not available in a generally usable form in the MSS spectral re­ ,--". /' sponse patterns; they must be generated from ancillary sources i, N ~"j I such as digital elevation models (OEM). 200 j(m. GENERAL GEOMORPHOMETRY AND \., DIGITAL ELEVATION MODELS \ ''( Terrain descriptors extracted from digital elevation models \,. may be related to the specific morphometry of landforms or the general geomorphometric characteristics of land surfaces. Spe­ \ cific geomorphometry is used to describe landforms that have " .v--.../". been delineated from adjacent parcels of land using clear and \. recognized geomorphological or genetic criteria. Examples can \ be found in analyses of cirques, drumlins, and stream channels. --"'" The system of general geomorphometry (Evans, 1972; Franklin, 1985) consists of measures of elevation, slope (first derivative of elevation), aspect (directional component of slope), convexity FIG. 1. Study area in the Ruby Range, Yukon Territory. (surface curvature or the second derivative of elevation), and relief (surface variability). Analysis results when subsets of such geomorphometric data are integrated with Landsat MSS images have been discussed such landscape criteria were conducted by interdisciplinary by Justice (1978), Fleming and Hoffer (1979), and Bonner et aI. mapping teams (Townshend, 1981; Hutchinson, 1978; Bastedo (1982), among others, for specific applications such as forest and Theberge, 1983). The Australian Surveys are perhaps the typing. In the present study, we discuss the significance of the best well known and documented examples of this approach, full range of general geomorphometric terrain descriptors. Those illustrating practical mapping results, philosophy, and methods terrain descriptors may contribute insight into the spectral and of terrain classification (Christian and Stewart, 1968; Paijmans, spatial linkages in the environment viewed in the interpretative 1970; Story et aI., 1976;
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