An automated approach to the classification of the slope units using digital data

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Geomorphology21 (1998) 251-264

An automated approach to the classification of the slope units using digital data
Philip T. Giles a, *, Steven E. Franklin b
a Department of Geography, Saint Mary's University, Halifax, NS B3H 3C3, Canada b Department of Geography, University of Calgary, Calgary, AB T2N 1N4, Canada

Received 15 June 1996; revised 12 May 1997; accepted 23 May 1997Abstract
Digital elevation and remote sensing data sets contain different, yet complementary, information related to geomorphological features. Digital elevation models (DEMs) represent the topography, or land form, whereas remote sensing data record the reflectance/emittance, or spectral, characteristics of surfaces. Computer analysis of integrated digital data sets can be exploited forgeomorphological classification using automated methods developed in the remote sensing community. In the present study, geomorphological classification in a moderate- to high-relief area dominated by slope processes in southwest Yukon Territory, Canada, is performed with a combined set of geomorphometric and spectral variables in a linear discriminant analysis. An automated method was developed tofind the boundaries of geomorphological objects and to extract the objects a~,~ groups of aggregated pixels. The geomorphological objects selected are slope units, with the boundaries being breaks of slope on two-dimensional downslope profiles. Each slope unit is described by variables summarizing the shape, topographic, and spectral characteristics of the aggregated group of pixels. Overalldiscrimination accuracy of 90% is achieved for the aggregated slope units in ten classes. © 1998 Elsevier Science B.V.
Keywords: automated analysis; classification; data processing; geomorphology

1. Introduction
Digital elevation models (DEMs) and remote sensing data contain important geomorphological information about characteristics of the surface. A grid DEM stores elevation values atregularly distributed points, from which characterizations of the form of the land surface can be estimated. These characterizations, such as slope gradient and profile curvature,

* Corresponding author. Tel.: +902 4205740; Fax: +902 4205122; E-mail:

have a variety of uses in geomorphometric applications (Pike, 1993) and in geomorphological and hydrological modelling (Mooreet al., 1991; Mitasova et al., 1996). Remote sensing devices, meanwhile, may record the electromagnetic reflectance (or emittance) properties of visible surfaces. For many landscapes in temperate climates the visible surface is vegetation, which masks the underlying soil or rock material (Adams and Adams, 1984; Warner et al., 1994). A strong link, however, often exists between vegetation and theunderlying geomorphological conditions (Howard and Mitchell, 1985; Pickup and Chewings, 1996). The potential for increased use of

0169-555X/98/$19.00 D 1998 Elsevier Science B.V. All rights reserved. PII S0169-555X(97)00064-0


P.T. Giles, S.E. Franklin/Geomorphology 21 (1998) 251-264

remote sensing data in geomorphological studies (Pickup, 1990; McDonnell, 1996) suggests thatinclusion of surface cover from remote sensing data should complement topographic data for more accurate hydrological models. In the present study, remote sensing data are used in two distinct ways: (1) utilizing spatial information contained in the data, an automated software package for generating DEMs from stereoscopic pairs of digital images is employed; and (2) reflectance information is usedas a surrogate measure of the surface characteristics, in turn related to geomorphological materials. The remote sensing data consist of a complementary pair of stereoscopic satellite images acquired in multispectral mode from Systbme Probatoire d'Observation de la Terre (SPOT). Based on the combined information available in the DEM and remote sensing data, discriminant analysis classifies...
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