Terrain Characterization using SRTM Data

Photonirvachak

J. Indian Soc. Remote Sens. (March 2010) 38: –

Terrain Characterization Using SRTM Data

Priyank Pravin Patel . Ashis Sarkar

Received: / Accepted:

Keywords

Priyank Pravin Patel1() . Ashis Sarkar2

1 Research Scholar, Department of Geography, PresidencyCollege, Kolkata.2 Professor and Head, Department of Geography,Presidency College, Kolkata.

e-mail: [email protected]

RESEARCH ARTICLE

Abstract Earth’s surface possesses relief because thegeomorphic processes operate at different rates andgeologic structure plays a dominant role in theevolution of landforms (Thornbury, 1954). The spatialpattern of relief yields the topographic mosaic of aterrain and is normally extracted from the topographicalmaps which are available at various scales. Ascartographic abstractions are scale – dependent,

topographical maps are rarely good inputs for terrainanalysis. Currently, the shuttle radar topographymission (SRTM) provides one of the most complete,highest resolution digital elevation model (DEM) ofthe Earth. It is an ideal data-set for precise terrainanalysis and topographic characterization in terms ofthe nature of altimetric distribution, relief aspects,patterns of lineaments and surface slope, topographicprofiles and their visualisation, correlation betweengeology and topography, hypsometric attributes andfinally, the hierarchy of terrain sub-units. The presentpaper extracts the above geomorphic features andterrain character of part of the Chotonagpur plateauand the Dulung River basin therein using SRTM data.

Introduction

S.O.I. Topographical maps, at a variety of map-scalesare the most readily available data source for terrainanalysis. But, the scale-induced cartographic

2 J. Indian Soc. Remote Sens. (March 2010) 38: –

constraints often restrict the accuracy of thetopographic database (tBase) as depicted by analmost infinite variety of the patterns of contourlayouts. The DEM data, on the other hand provides avery enticing and feasible option for generating areliable database of the earth’s surface. A DEM hasbeen defined as a regular gridded matrix representationof the continuous variation of relief over space(Burrough, 1986). The attraction of a simple matrix ofelevation values was one of the most importantreasons for its uptake in the early 1970s as a modelsuitable for landscape analysis (Evans, 1972). Asmathematical–statistical models can be easily builtby well-defined algorithms, digital manipulation andvisualization of tBase becomes easier. Thus, as amodel of surface form, the steady and widespreaduse of DEM may be attributed to its easy integrationwithin a GIS environment (Weibel and Heller, 1991).

The Shuttle Radar Topography Mission (SRTM)was a joint venture of National Aeronautics and SpaceAdministration (NASA’s) Jet Propulsion Laboratory(JPL), National Imaging & Mapping Agency (NIMA),and the German and Italian Space Agencies (Werner,2001). Using the spaceborne imaging radar (SIR–C)and X–band synthetic aperture radar (X–SAR)hardware that flew twice on the space shuttle‘Endeavour’, the mission collected 12 terabytes ofdata covering the entire globe (60ÚN – 60ÚS) inFebruary 2000 in about 10 days, mapping some of theleast accessible regions of the world. The DEMscurrently distributed by the United States GeologicalSurvey (USGS) were derived from interferometricanalysis of the C– band signal and were processedby NASA (Farr & Kobrick, 2000).

The SRTM data are distributed at two levels %SRTM1 (for the United States and its territories /possessions) with data sampled at 1 arc-sec intervals,and SRTM3 (for rest of the world) sampled at 3 arc-sec. The 3 arc-sec data are generated by (3 x 3)averaging of the 1 arc-sec samples and has anaccuracy of ±16m, far greater than that of even a1:25,000 scale topographical map. The SRTM3 dataare divided into (1Ú x 1Ú) tiles and distributed asheight files with *.hgt extension. File names refer tothe latitude and longitude of the lower left corner of

the tile, e.g., N22E086 has its origin at the lower leftcorner at (86ÚE, 22ÚN). Each pixel in SRTM3 data isabout 90m in extent. Heights are referenced to theWGS84 / EGM96 geoid in meters and data voids areassigned a value of -32768. Each SRTM3 file contains1201 lines and 1201 samples per line (Rodriguez, etal., 2005).

Study Area

The present study area lies between 22°N – 23°N and86°E – 87°E and comprises parts of Purbi Singhbhumand Paschimi Singhbhum districts (Jharkhand),Bankura, Medinipur and Puruliya districts (WestBengal) and Mayurbhanj district (Orissa), coveringthe Singhbhum Shear Zone and its surroundings anddrained by the Subarnarekha, Kadkal and Kangsabatirivers and their tributaries. It is a diverse landscape,with residual hills, dissected plateaus, escarpmentsand rolling plains, as can be deciphered from visualinterpretation of the SRTM DEM of the area (Figure1), and thus, well suited for the ensuing analysis.

Objectives

The objectives of the present study are to characterizethe terrain of the Dulung river basin using SRTM DEMin terms of the ¯• nature of the altimetric frequency distribution.• relief aspects through the delineation of ‘pits’

and ‘peaks’.• patterns of lineaments and surface slope.• geometric properties of the topographic profiles

and their visualisation.• correlation between underlying geology and

surface topography.• hypsometric attributes of the terrain.• hierarchy of the terrain sub- units.

Methodology

The methodology followed for the present study isas follows (Figure 2):

3J. Indian Soc. Remote Sens. (March 2010) 38: –

Fig. 1 Location of the Study Area.

Fig. 2 Flowchart of the Work process


• Digitization of Survey of India (S.O.I.)Topographical Maps (73J – R.F. 1:250,000 forterrain characterization and 73J/10, 11, 14, 15, 16– R.F. 1:50,000 for terrain correlation withgeology).

• Procuring the SRTM-DEM file from Unites StatesGeological Survey (USGS) – file N22E086.

• Importing the STRM DEM *.hgt format files intothe TAS (Terrain Analysis System) software,followed by the operations of ‘pit removal’ and‘depression filling’ to eliminate gaps in the data.

• Extraction of altimetric histogram and slopeprofiles from the SRTM DEM to characterize thevarious terrain attributes of the study area andtheir hypsometric analysis.

• Contour generation and preparation of relief andslope maps of the study area from the SRTMDEM.

• Delineation of distinctive terrain units based onabove analysis for the study area and co-relationof the same with the underlying geology obtainedfrom G.S.I. Jamshedpur Quadrangle Map 73J –R.F. - 1:250,000. for the Dulung River Basin(situated in south-eastern sector of study area).

Data manipulation and analysis

Data Pre-Processing

While the data coverage of SRTM is global, someregions are missing data due to lack of contrast in theradar image, presence of water or excessiveatmospheric interference. Such data voids are usuallyalong rivers, in lakes and in steep regions and oftenon hillsides having similar aspect due to shadowing.Any such gaps or data voids must be filled in toproduce a continuous and contiguous surface beforefurther manipulations. Often, DEMs contain extensiveflats (areas of equal elevation). Usually, cells within aflat region do not have down-slope neighbours, andtherefore, computation of surface slope becomesdifficult (Bamler, 1999). Such ‘digital flats’ sometimesreflect minor features in the real landscape and arenormally preserved during processing. If their removalallows a more robust surface generation, then they

are erased after confirmatory checks usingtopographical maps of the area concerned. A correctedDEM is thus finally generated from the raw data forensuing analysis.

Cell Altimetric Distribution

The SRTM tile of the study area comprises 1,442,401grids with elevation ranging between 10 m and 930 m.Each cell has an area of 8100 m2. Using the DEM cellvalues, an altimetric frequency histogram (Figure 3)has been generated with 10 m class interval. It givesthe nature of the ‘area–altitude’ distribution of thestudy area, as follows ¯• It is a positively skewed frequency distribution

of elevation with tail towards the higher values.• It is a multimodal distribution with principal mode

in the elevation classes of (80 – 90) meters.• The auxiliary modes are located in the elevation

ranges of (130 – 140 m), (150 – 160 m), (240 – 250m), (330 – 340 m) and (400 – 410 m).

• Within the topographic amplitude of 920 m, about25% of the area lies between the elevation rangesof (30 – 110 m), 50% of the area between (30 – 170m), and 75% of the area between (30 – 260 m).

• Obviously, only 25% of the area lies between theelevation range of (260 – 930 m).

Relief Aspects and Pit – Peak Delineation

In any landscape, the two extremes of topographiccharacter are the depressions or pits and the peaks or

Fig. 3 Altitudinal Frequency Histogram


unobstructed rises in the topography, with theremaining surface grading from one to the other. Pitsprovide clues to flow accumulation and being the anti-thesis of peaks, point towards regions where thesemay exist. Pits are observed primarily along broadstream courses and along the base slopes ofprominent ridges where flowing water accumulatesdue to decreasing channel gradients and subsequentchecks in flow velocity. These then, also indicatezones of pediment formation and possible talus fanor cone development.

A relief image of the study area (Figure 4) clearlydepicts the valleys of the major streams, especiallythe Subarnarekha river. Its is narrow, incised, ofstraight configuration and steep gradient in the centralpart of the image, grading to broad and meanderingwaves in the south-eastern part which has muchgentler surface gradient. The Dulung and the Kasairivers, both occupy similar gentle valleys. The north-western and south-western sectors appear morerugged relative to their eastern counterparts,displaying prominent ridges.

Peaks are grids of high elevation that rise abovethe surrounding cells. The fundamental parametersfor the delineation of the possible topographic peakzones are – absolute relief, threshold slope angle andslope tolerance (Wood, 1996b). The thresholds havebeen defined as: minimum altitude of 600 m, a gradientof 45Úor more and at least 1.5 times steeper thanneighbouring cells. The above criteria removes anyambiguity during peak classification that might haveseen steep river banks classified as ‘peaks’ if onlyslope angle was considered or whole plateau surfacesbeing classified likewise if only absolute elevationwas considered. The slope tolerance value furtherprunes the search for a progressively sharply risingland unit, from which a maximum viewshed can beobtained. Expectedly, peak zones fall in the ruggedwestern half of the study area, away from the broadflat plains of the east. A large contiguous peak zoneis seen in the south western sector, representing achain of high hills while the Dalma hills show upclearly as peaks in the north (Figure 4.).

Fig. 4 Study area relief image showing Major Streams & Terrain Features


Lineaments and Surface Slope

The Subarnarekha valley shows up in stark contrast(in dark tint) to the surrounding areas; numerousstreams that originate from the hills and plateaus anddissect them have formed fine mesh / finger-likepatterns and finally flow into the main river, especiallyalong its left bank. Being characterized by steeperslopes, higher hills and plateaus, the south westernsector of the image appears contrastingly distinctivefrom the south eastern sector, which comprises a vastexpanse of very gentle plains, imperceptibly gradinginto one another. The landforms around the Kasaivalley in the north-east show a mix of low dissectedplateaus and small hills along with gentle and broadplains.

The alternating ridge-valley configuration of theSinghbhum Shear Zone (SSZ) shows up prominentlyin the north and is distinct from the surrounding hillsdissected lower plateau surfaces and plains. Thesurface slope is derived by computing the gradient ofeach cell. Peak areas and ridges in the west have thehighest values and the eastern plains lowest values,while the intervening plateaus, the values in between(Figure 4).

Topographic Profile Analysis and 3DVisualisation Surface profile analysis is done throughthe enumeration of the elevation values of the cellsacross which a profile line passes. Six ‘representative

profiles’ are taken to identify the various topographiclevels, terrain components and their individualcharacteristics (Figure 5). The major observations(Table 1) are ¯• The Subarnarekha valley has an incised trough

upstream as it cuts through the plateau floor anda low, very gentle and broad valley floor in itslower reaches.

• The similar broad flat plains of the Kasai river inthe north eastern sector.

• The Dalma range having high altitude and steepslopes lies in the north and similar hills are alsofound in the southwest.

• The jagged sharply rising hills and plungingincised valleys are found in the SSZ withalternating ridge–and–valley configuration.

• The dissected higher plateau surfaces arecharacterized by steep escarpments.

• The low residual hills flank the higher plateausurfaces.

• The much dissected lower plateau surface gentlygrades into the flood plains.

• The small residual hills / mounds are found in thesouth eastern sector.To compare the topographic levels and their

progressive changes along latitudinal and longitudinaldirections, sets of serial profiles have been extractedand superimposed. Each horizontal or vertical profileline passes over 1201 cells covering a total distance

Table 1 Accordant Summit Levels Ascertained from Profile Analysis

Topographic Unit Elevation Range (m) Attribute

Gentle rolling plains below 100 Erosional plainLowest accordant summit level 100 – 120 Erosional plainSecond accordant summit level 140 – 160 Erosional plainThird accordant summit level 200 – 220 Erosional plainFourth accordant summit level 360 – 380 Plateau rimFifth accordant summit level 480 – 500 Plateau rimSixth accordant summit level 680 – 700 Plateau properSeventh accordant summit level 860 – 880 Plateau properHighest peaks above 880 Peak


Fig. 5 Profile taken across the study area

of 108.09 km. The superimposed horizontal profilesshow distinct terrain units. From west to east, theseare: dissected higher plateau, higher hills, highestpeaks, lower hills, dissected lower plateau and gentleplains. Thus, the western section is more rugged withhigh hills and peaks. A central zone of much dissectedand incised hills lies betwixt the higher hills and

plateaus of the west and rolling plains of the east.The superimposed vertical profiles show similarterrain units and reveals how the land grades betweenthe various topographic levels. There is a starkdifference in altitude between the two adjacentaccordant summit levels / planation surfaces in thesouthern zone of the image while the northernplanation surface stands betwixt the former two, towhich they both either grade up or grade down. Thegreater ruggedness of the southern section isemphasised while its northern counterpart has somelow hills and the odd high peak. The lower plains inthe central area abut to either of the above.

Taken together, the attributes of the horizontaland vertical profiles suggest that the south westernsector is the most rugged while the south easternsector is the most gentle. Lying adjacent to each other,they result in an abrupt rise in surface elevation andslope as one travels from the east to the west. Profilestatistics have been enumerated to mathematicallydeduce the nature of relief along them by computingthe mean elevation, range, standard deviation andgrid-to grid altitudinal difference of the 1201 cells thatlie along each profile line (Figure 6). Clear distinctionsare present between the computed statistics for thelatitudinal profile lines (LPL) and those for themeridional profile lines (MPL).

The graph of profile line-wise mean elevationreveals an almost uniform mean elevation apart froma slight dip in the middle section (over valleys) forthe LPL since these profiles traverse over bothplateaus and plains. On the other hand, the meanelevation graph for the MPL reveals grading of thelandscape from west to east with markedly lower meanelevations in the east where the MPL traverse almostexclusively over low plains. As a result, thecorresponding range of elevations is much lower forMPL (except where some of them pass over analternating ridge-valley zone like the SSZ), while theyare much higher for LPL since they represent bothtopographic highs and lows. There are thus, fewerabrupt changes within the maximum and minimumcell-to-cell elevation-difference lines for the MPL astheir amplitude of relief is lower than that of the LPL.For the MPL, in the east the maximum and minimum


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elevation lines almost converge suggesting a flatlandscape with very low relative relief. Standarddeviation values are much lower for the MPL sincethey pass over much more uniform individual terrainunits than across diverse terrain facets as do the LPL.Thus there is a stronger correlation between the rangeand standard deviation values for the MPL than forthe LPL.

It appears that in the study area the MPLs ratherthan the LPLs yield better performance indiscriminating and delineating the terrain units fromwest to east (following MPL) as this minimises intraterrain-unit anomalies in relief and morphometricaspects. Using DEM data like SRTM certainly makesthis otherwise laborious process, quicker and simpler.Three-dimensional (3-D) visualisations generated forvarious sites in the study area depict the aboveoutlined and profiled terrain units and corroboratesthe pertaining discussion (Figure 7).

Thus, the analysis of profiles suggests that theterrain comprise three major divisions ¯ plateauproper, plateau rim and erosional plain (Table - 2).

Erosional plains have been further subdivided intofour sub–units, plateau rim into two sub–units andplateau proper into three sub–units. Spectacularaccordant summit levels are distinctive in the plateauproper and plateau rim regions. These are suggestiveof uplifted peneplains / planation surfaces.

Correlation between Geology and Relief

Apart from regional climate, it is the regional geologicalstructure that most controls the operations of theexogenous processes, developing thereby theexisting matrix of relief. The geology of the Dulungbasin, situated in the south-eastern sector of thestudy area has been studied and correlated with itstopographic mosaic. The basin lies on the easternfringe of the Chotonagpur plateau, just to thesoutheast of the SSZ. The area mainly comprises theCenozioc sediments with some basic and ultrabasicvolcanics and associated sediments formed asintrusives within the geosynclinal to platform meta-sediments of schists, phyllites and quartzites. Thebasin exposes a wide area of Tertiary and Quaternary

Fig. 7 3-D views of portions of the study area generated from the SRTM DEM clearly depicts the different terrain faces& various planation surfaces.


Table 2 Demarcated Terrain Attributes from Profile Analysis

Topographic Unit Altitudinal Attributes Major Divisions Sub – divisions Level (m)

1. Erosional Plain1(a) Gentle Plains below 100 Distinct topographic levels;1(b) Gently Rolling Plains 100 – 120 Ruggedness rapidly vanishes towar1(c) Undulating Plains 140 – 160 lower plains; Shallow and wide1(d) Rugged Plains 200 – 220 valleys; Fewer residual hills.

2. Plateau Rim 2(a) Moderately Dissected Zone 360 – 380 Accordant summit levels distinctive;2(b) Highly Dissected Zone 480 – 500 Open valleys; Rugged terrain.

3. Plateau Proper 3(a) Moderately Dissected Zone 680 – 700 Accordant summit levels distinctive;3(b) Highly Dissected Zone 860 – 880 Narrow valleys; Conical Peaks;

3(c) Highest Peaks above 880 Most rugged terrain

sediments, horizontally lain with shales, conglomeratesand Dhalbhum laterites. The width and thickness ofthe Quaternary sediments increase towards south andeast of the basin. The northwest portion of the basinis geologically much more complex consisting mainlyof garnetiferous phyllites of the Singhbhum Group(lower Proterozioc) that dips towards NNE at an angleof 70° while its foliation planes dip towards SE at anangle of 55°. The northwestern part of this bed isoverlain by carbon – phyllite intrusives containingquartzite bands, both being the members of the DalmaVolcanics (lower Proterozioc). The carbon – phyllitebeds dip towards SE at an angle of 60° while itsfoliation planes dip towards NW at an angle of 60°.There is an arm like intrusion southwestwards ofgarnet – staurolite schist with kyanite belonging tothe Singhbhum Group. In the central part, some bandsof quartzites belonging to the Dalma Volcanics arepresent (Figure 8).

The upstanding portion of the basin areacoincides with areas of crystalline and metamorphicrocks, while the sedimentaries underlie the lower,gentle river valley floors. This relation holds true forthe entire study area, where the upstanding ridgesare underlain by harder metamorphics and the valleysmainly by quaternary gravels.

Terrain Hypsometry

Historically, hypsometry has been used as anindicator of the geomorphic form of the catchments

and landforms. Computationally, it refers to findingthe distribution of elevations as a function of areaoccupied by each contour interval within a terrainunit. The idea of hypsometry was first introduced byLangbein et al (1947) and was later extended byStrahler (1952). Using dimensionless parameters suchas proportionate area and proportionate altitude,hypsometric curves can be plotted, described andcompared irrespective of the true absolute scale.Curves show distinctive differences both in sinuosityof form and in proportionate area below the curve,termed as the hypsometric integral (H.I.). Thegeometry of hypsometric curve and the magnitude ofthe hypsometric integral together describe the stageof evolution of a landscape (Strahler, 1957). Hence,the shape of the curve, the hypsometric integral andthe regression parameters of the best-fit statisticalcurves can be conveniently used as descriptiveparameters for the purpose of comparison andclassification and to determine the stage of alandscape in the evolutionary process. Based on theH.I., a landscape can be genetically classified in termsof the stage of evolution as youthful (H.I. > 0.5),mature or in equilibrium (H.I. = 0.5) or old (H.I. < 0.5),(Strahler, 1957).

The hypsometric curve of the study area (Fig. 9)is steeply concaved upwards – indicative of alandscape in the “old stage” of the normal cycle of


erosion. This is further confirmed by the magnitudeof hypsometric integral (0.18), implying that of theoriginal landmass of the basin area, only 18% is stillleft to be denuded away and reduce the entire regioninto a flat, almost featureless plain. The H.I. is inaccordance with the tectonic and denudational historyof the area. The area is tectonically relatively stablewith little or no uplift in the recent geologic past. Themajor stream coursing through the area, theSubarnarekha River, being a superimposed river, hasbeen gouging out the landscape for eons, reducing itto the present, largely gently, undulating state withsome remnant uplands still holding out against theravages of exogenous agents and time.

Delineation of Terrain Units

Altitudinal frequency analysis, relief-slope-hillshadeanalysis, surface profile analysis, 3D visualisations

Fig. 9 Hypsometric Curves and integral for Study areaDEM.

Fig. 8 Tilted 3-D view of the Duling N-Basin looking Northwest-ward from its mouth and litho-cover of the Duling N-Basindraped over the D.E.M. of the basin.


and finally correlations with the geology enableclassifying the study area into distinctive terrain units.To further derive guidelines for this, fractal statisticsof the SRTM DEM have been derived using therelevant module in Landserf software. The fractaldimension (F.D.) has been computed by selecting afixed interval lag and computing the standardvariogram for the surface based on this lag, assumingan isotropic process, and then plotting the log of thelag against the log of the variogram. The fractaldimension for the above surface varies between 2 to3 with a mean value of 2.83. The two extremes are thewestern higher hills and ridges (F.D. ~ 2) and theeastern broad valley flats (F.D. ~ 3).

As outlined before, the various terrain units aremainly distinguished on the basis of their differingelevation ranges (summarised from the various rangesestimated earlier) and as such, contours are primarilyused for demarcating their extents. Contours for thestudy area have been obtained via digitisation of theconstituent topographical maps. Where moresensitive contours were required (lesser contourinterval values), these were generated from the SRTMDEM. The two datasets fused together complementeach other and enable better the eventual terrain unitdelineation (Figure 10). The demarcated units showstrong correlation with the geology and slope of thearea. The upstanding segments of the terrain are of

Fig. 10 Terrain classification of the Study Area DEM.


much less spatial dimension. It is the lower elevationclasses that dominate with the gentle plains anddissected lower plateau covering over half the maparea (Table 3), suggesting a much denuded landscapewith remnant higher hill and residual ridges.

Conclusion

The SRTM mission achieved what conventionalcartography had failed to achieve in three centuriesof its existence—to generate a uniform-resolution,uniform-accuracy elevation model of most of theearth’s surface. SRTM DEM usage can facilitatetopographic analysis and is a good backup in casetopographic maps are not available or that data needsto be enhanced. However, using the SRTM data justfor the sake of using it, will lead to dilution of itsimportance and will lead to ignoring of the much richergeo-spatial content of topographic maps. The resultsobtained from SRTM grid processing should alwaysbe corroborated with available maps or non-spatialdata. Despite being a model of continuous surfaceform, a DEM is a set of discrete elevationmeasurements of what is usually an undifferentiatablesurface. The fidelity with which the DEM models thetrue surface will depend on the surface roughnessand DEM resolution. Yet, fractal logic suggests thatthere will always be detail at a finer scale than thatmeasured at the DEM resolution. Thus, all DEMs

implicitly model at a certain scale implied by the gridcell resolution (Garbrecht and Martz, 1993; Ackerman,1993 and Hodgson, 1995). Although the scaledependency of measurement has been recognised andeven modelled by many authors it still remains hiddenin many aspects of DEM analysis. Axiomatically, ahigher DEM resolution results in more accuratemodelling.

References

Ackermann, F. (1993). Automatic generation of digitalelevation models, presented at OEEPECommission B, DTM Accuracy Meeting,Southampton. 16 pp

Bamler, R. (1999). The SRTM Mission – A World-Wide30 m Resolution DEM from SAR Interferometry in11 Days. Photogrammetric Week. 47: pp. 145-154

Burrough, P.A. (1986). Principles of GeographicalInformation Systems for Land ResourcesAssessment. OUP, Oxford, Ch.8, Methods ofinterpolation, pp. 147-166.

Evans, I. S. (1972). General geomorphometry,derivatives of altitude, and descriptive statistics.in Chorley, R. J. ed. Spatial Analysis inGeomorphology, Methuen, London. pp.17-90.

Farr, T.G., and M. Kobrick, (2000), Shuttle RadarTopography Mission produces a wealth of data,Amer. Geophys. Union Eos, 81, pp. 583-585.

Table 3 Demarcated Terrain Class Statistics

Land Unit Elevation No. of Mean Elevation StandardClass Class Cells Elevation Range Deviation (m) (m) (m)

I Broad, gentle valley 30 - 100 233076 76.3097 70 15.609II Dissected lower plateau 100 - 225 449202 156.799 125 35.0231III Dissected higher plateau 225 - 375 284860 284.384 150 40.5975IV Steep pediments 375 - 500 57445 426.677 125 34.2011V Higher hills 500 - 750 26185 593.507 250 68.2072VI Highest peaks 750 - 930 2464 801.12 130 40.3836


Garbrecht, J. and Martz, L. (1993). Grid size dependencyof parameters from digital elevation models, 12pp. (source unknown)

Hodgson, M.E. (1995). What cell size does thecomputed slope / aspect angle represent?Photogrammetric Engineering and RemoteSensing, 61(5), pp. 513-517.

Langbein, W. B., et al., (1947). Topographiccharacteristics of drainage basins. USGS Water-Supply Paper, 968-C: pp. 125-158

Rodriguez, E., C.S. Morris, J.E. Belz, E.C. Chapin, J.M.Martin, W. Daffer and S. Hensley, (2005), Anassessment of the SRTM topographic products,Technical Report JPL D-31639, Jet PropulsionLaboratory, Pasadena, California, pp. 143

Shuttle Radar Topography Mission DTED ® Level 1(3-arc second) documentation. http://edcsns17.cr.usgs.gov/srtm/index.html

SRTM Documentation. ftp://edcsgs9.cr.usgs.gov/pub/data/srtm/Documentation/SRTM_Topo.txt

Strahler, A. N. (1952). Hypsometric analysis oferosional topography, Geol. Soc. Amer. Bull., 63,pp. 117- 1142.

Strahler, A. N. (1957). Quantitative analysis ofwatershed geomorphology, Trans. Amer.Geophys. Union., 38, pp. 913 – 920

Thornbury, W.D. (1954). Principles of Geomorphology,Chapman and Hall, London.

Weibel, R. and Heller, M. (1991). Digital TerrainModelling. in: Maguire, D. J., Goodchild, M. F.,and Rhind, D. W. (eds.) GeographicalInformation Systems: Principles andApplications, pp.269-297, Longman, London.

Werner, M., (2001), Shuttle Radar Topography Mission(SRTM), Mission overview, J. Telecom.(Frequenz), 55, pp. 75-79.

Wood, J. (1996b). The geomorphologicalcharacterisation of digital elevation modelsUnpublished PhD thesis, Department ofGeography, University of Leicester (http://www.soi.city.ac.uk/~jwo/phd)

Wood, J. (2002a). Landserf: visualisation and analysisof terrain models (http://www.landserf.org/)

Terrain Characterization using SRTM Data

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