Quantification of surface sciences. Slopes measured from digital elevation models or other topographic data sets depend strongly on the length scale or window size used in the slope calculations. The spectrum of slope distributions as a function of length scale is related to the variation relief as a function of scale, and may reflect the length scales the processes acting to form the surface morphology. Small window sizes, approaching the grid spacing, can yield reliable slope determinations if good quality data sets are available. There is a strong variation in the data quality among DEM's, with a second DEM poorly representing slopes in the Hills, California area, The slopes measured from a standard 30-m DEM and high-resolution TOPSAR DEM match each other well at length-scales greater than 30 means for the rugged Verdugo Hills change from 15 to 26 as the calculation window size decreases from 270 m to 15 m. Importance of Slope The accurate measurement of the slope angle of the ..