Regional Geomorphic Parameters

MICRODEM computes a series of parameters for a region, with the region size determined by the user.  The variables include:

• ELEV_AVG, ELEV_STD, ELEV_SKW, ELEV_KRT: the first four moments of the elevation distribution, computed with the formulas in Press et al. (1986).  ELEV_STD correlates strongly with slope.

• ELEV_MAX: the maximum elevation in the block.  This can find data anomalies and blunders, in addition to any geomorphic significance.

• SLOPE_AVG, SLOPE_STD, SLOPE_SKW, SLOPE_KRT: moments of the slope distribution in percent (100*rise/run).  Slopes were computed with an eight neighbors unweighted algorithm (Evans, 1998; Florinsky, 1998; Sharpnack and Akin, 1969).  The algorithm has little effect on the results; Guth (1995) and other studies have shown extremely high correlations between all available slope algorithms. The units (percent or degrees) also appear to have little impact.

• SLOPE_MAX: largest slope (percent) in the sampling region.  While this is largely of value for detecting blunders during DEM creation, it also has geomorphic significance.

• PLANC_AVG, PLANC _STD, PLANC _SKW, PLANC _KRT: moments of the plan curvature distribution, computed with the formulas in Press et al. (1986).  Curvature computed with the equations in Wood (1996) based on earlier suggestions from Evans.

• PROFC_AVG, PROFC _STD, PROFC _SKW, PROFC _KRT: moments of the profile curvature distribution, computed with the formulas in Press et al. (1986).  Curvature computed with the equations in Wood (1996).

• S1S2, S2S3, FABRIC_DIR: Computed (Guth, 2003, following  Chapman, 1952 and Woodcock, 1977)  using logs of the eigenvectors v[1] (largest) to v[3] (smallest) of the surface normal vector distribution.  S1S2 measures flatness (a logarithmic inverse of slope), S2S3 measures terrain organization, and FABRIC_DIR gives the dominant direction of ridges and valley.  Because FABRIC_DIR measures circular angles, its statistics have anomalies.

• s1s2 := ln(v[1]/v[2]);

• s2s3 := ln(v[2]/v[3]);

• SHAPE, STRENGTH: Fisher et al. (1987, pp.48, 159) defined these ratios of the logs of the eigenvectors, defined somewhat differently that those used by Woodcock (1977) and Guth (2003). Strength and S1S2 generally correlate closely, while S2S3 and shape correlate moderately

• Shape := ln(v[1]/v[2])/ln(v[2]/v[3]);

• Strength := ln(v[1]/v[3]);

• ELEV_RELF:  elevation relief ratio ( [AveZ-MinZ] / [MaxZ – MinZ]) computed for a region (Pike and Wilson,1971; Etzelmuller, 2000); equivalent to the coefficient of dissection (Klinkenberg,1992 after Strahler,1952).

• GAMMA_NS, GAMMA_EW, GAMMA_NESW, GAMMA_NWSE: Nugget variance, Co, from the variogram (Curran, 1988).  This is a measure of the elevation difference from each point to its nearest neighbor in four directions; smaller values reflect smooth terrain, and high values rougher terrain.  All four turn out to be very highly correlated with each other, and with other measures of slope.

• ROUGHNESS: Measure correlating strongly with slope (Mark,1975; Etzelmuller, 2000).

• RoughnessFactor := 1 - sqrt(sqr(x1sq) + sqr(y1sq) + sqr(z1sq)) / NumPts;  (the three numbers are the sums of the squares of the three components (directional cosines) of the normal vector to the earth's surface)

• RELIEF: difference between the highest and lowest elevations within the sampling region (Drummond and Dennis, 1968).

• Upward and Downward openness moments:

• MISSING: the percentage of holes in the SRTM data.  This can be used to filter the results, and only look at statistics where missing data might bias the results.

Key Parameters (Guth, 2006)

Last revision 10/19/2017