Spectral Analysis of Landforms∗

Variance spectrum analysis is adapted to topographic profiles obtained from 1:24,000 contour maps for five contrasting areas in the United States. The one-dimensional spectrum describes four independent aspects of topography: magnitude of landform periodicities, spacing of periodicities, overall roughness, and contrast between slopes of large and small features. The latter three attributes are expressed numerically for landform classification and other geomorphic problems. The digital filter and sample design used here limited resolution of the technique to 240–3,700 meters, although longer wave lengths at 1:24,000 are added easily. Some sampling problems remain unsolved. Linear regressions of spectral functions on logarithmic scales facilitate subsequent analysis. Spectra of apparently random topography can show marked periodicities, especially in areas of dendritic drainage.