SHORT NOTE

Remote Sensing Study of Sittampundi AnorthositeComplex, India

S. Anbazhagan & N. K. Sainaba & S. Arivazhagan

Received: 28 October 2009 /Accepted: 24 May 2011 /Published online: 25 June 2011# Indian Society of Remote Sensing 2011

Abstract In the present study, The Landsat 7 ETMsatellite data was collected for the Sittampundianorthosites complex and digital image analysis wascarried out. The anorthositic rocks available atSittampundi complex is considered as an equivalentof lunar highland rocks. Hence, a remote sensingstudy comprises of image analysis and spectral profileanalysis was carried out. The satellite data wasdigitally processed and generated various outputs likeband combinations, color composites, stretched out-puts, and PCA. The suitable processed outputs wereidentified for delineating the anorthosite complex.The diagnostic absorption features of reflectancespectra are the sensitive indicators of mineralogyand chemical composition of rocks, which are interestto the planetary scientists. The spectral profile ofLandsat ETM plotted for pure and mixed anorthositepixels and compared with the field and lab reflectancespectra. The percentages of image spectra vary from30% to 60% for Sittampundi anorthosite. The spectralbands 2, 4 and 6 have low reflectance and bands 3 and 5

have high reflectance. The spectral range of bands2,3,4,5 and 6 are 525 nm–605 nm, 630 nm–690 nm,750 nm–900 nm, 1550 nm–1750 nm and 10400 nm–12500 nm respectively. The field spectral curve hasweak absorptions at 650 nm and 1000 nm due to the irontransition absorption and low ca- pyroxene respectivelyavailable in the anorthosite, matching with the imagespectra. However, hyperspectal image with narrowbandwidth could be more useful in selecting the suitablespectrum for remotely mapping the anorthosite region,as equivalent test site for lunar highland region.

Keywords Sittampundi anorthosite . Image analysis .

Spectral profile . Remote sensing

Introduction

Remote sensing technology has been widely used fordiscrimination of various lithology and mineraldeposits. (Gupta 2005). It has reached into newerdimensions by advent of imaging spectroscopy inidentification of minerals and rocks. The rock typemapping through remote sensing data normally startswith the measurement of ground reflectance spectra,lab spectra and digital image processing of satellitedata. Extensive studies had been carried out to collectthe reflectance spectra of various rocks and mineralsthrough ground spectroradiometric survey (Goetz etal. 1975; Deering 1989; Ramasamy et al. 1993;Milton et al. 1995; Teillet 1995). Remotely obtainedspectra in the visible and near infrared region canprovide information on the mineralogy, modal abun-

J Indian Soc Remote Sens (March 2012) 40(1):145–153DOI 10.1007/s12524-011-0126-y

S. Anbazhagan :N. K. Sainaba : S. Arivazhagan (*)Department of Geology, Periyar University,Salem 636 011, Indiae-mail: arivusv@gmail.com

S. Anbazhagane-mail: anbu02@gmail.com

N. K. Sainabae-mail: sainus@gmail.com

S. ArivazhaganPLANEX, Physical Research Laboratory,Ahmedabad 380 009, India

dance of the planetary surface (Adams 1974). In thiscontest, the Sittampundi anorthosite complex is con-sidered as an equivalent of lunar highland region. Themoon surface is mainly composed of mare basalts,highland anorthosites, KREEP rocks (Ouyang 1989;Pieters and Englert 1997; Lodders and Fegley 1998)and the surface materials variable in composition(Heiken et al. 1991). The highland region comprisesof ferron anorthosites, Mg rich rocks mainly norite,tractolite and dunite. The KREEP rock comprises ofPotassium, Rare Earth Elements and Phosphorous.(Lodders and Fegley 1998). In the present study,digital image processing of Landsat 7 ETM satellitedata was carried out for Sittampundi anorthositecomplex. The study emphasis the spectral behaviorof anorthosites in satellite imagery under visible andnear infrared region. Further, the different enhance-ment techniques utilized in image processing isuseful to adopt similar procedure for remotelysensing of lunar highland region. This type of study

is useful in the context of ISRO’s initiatives to sendseries of missions to the moon for selenologicalexploration.

Sittampundi Anorthosite Complex

Anorthosite is a plagioclase-rich igneous rock withsubordinate amount of pyroxenes, olivine and othermafic minerals. Sittampundi anorthositic complex isdominated by relatively pure calcic anorthite (An80-100) with less than 10% mafic minerals (Ashwal2000). Anorthosite samples returned from Apollomissions contains >90% Ca-rich plagioclase as wellas pyroxene and minor amount olivine, which are ironrich (Heiken et al. 1991; Peterson et al. 1997). Thesimilarity of the mineralogy and relative percentage ofmajor oxides in Sittampundi anorthsoite is consideredas equivalent of lunar highland anorthisitic rock(Anbazhagan and Arivazhagan 2010). The Sittam-

Fig. 1 Location map of the Sittampundi Anorthosite complex

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pundi anorthosite complex is located in Namakkaldistrict, Tamil Nadu, India in between northernlatitude 11° 10″ 0′–11° 20″ 0′ and eastern longitude77° 50″ 0′–78° 0″ 0′ (Fig. 1). The anorthositecomplex exposed over the strike length of 22–25 km. It has been folded, deformed and boundedQuartzo feldspathic hornblende biotite gneiss (Ram-adurai et al. 1975). Sittampundi complex occurs onthe Moyyar-Bhavani-Cauvery tectonic zone. The Sm–Nd isotope studies of Sittampundi anorthosite com-plex had given an age of 2935±60 Ma indicatingArchean period. It occurs as a layered igneous bodyand forms a part of the granitic terrain of southIndia. Chromite occurs exclusively within theanorthosite as discontinuous bands/ lenses. Thelayered sequence of meta-anorthositic gneissescontaining chromitite bands and eclogite-gabbrosare exposed in an arcuate belt (Subramaniam 1956).The other lithological units surrounding the studyarea are hornblende biotite gneiss, pink migmatite,amphibolite, Tiruchengode granite and charnockite(Fig. 2) (GSI 2005). The ultra basic and basicintrusive comprises of pyroxenite, dolerite, peridotiteand gabbro.

Materials and Methods

The Landsat 7 ETM satellite data acquired in 1999has been used for discriminating lithological contactand spectral extraction of anorthosite. ERDAS imag-ine 9.0 image processing software is used to digitallyprocess the satellite data and extract the spectralcharacteristics. The specification of Landsat ETMsatellite data is given in Table 1.

Image Analysis

The purpose of the image analysis is the discrimina-tion of anorthosite from rest of the lithology andoptimizes the suitable image processing techniques.The Landsat 7 ETM Satellite data digitally processedand generated various outputs. Out of 7 bands ofETM satellite data, only first 5 bands were utilized forimage analysis. The image processing techniqueconsists of band combinations, stretching and Princi-ple Component Analysis. Through band combina-tions, False Color Composite (FCC), True ColorComposite (TCC) and Pseudo Color Composite

Fig. 2 Geology of Sittampundi Anorthosite Complex (after GSI 2005)

Table 1 Specification of Landsat 7 ETM sensor

Band Spectral resolutionin μm

Spatialresolution

1 0.450–0.515 30×30

2 0.525–0.605 30×30

3 0.630–0.690 30×30

4 0.750–0.900 30×30

5 1.55–1.75 30×30

6 10.40–12.50 60×60

7 2.09–2.35 30×30

Sensor TechnologySwath Width

Scanning Mirror Spectrometer185 km

Data Rate 250 images per day @31,450 km2

Revisit 16 days

Orbit and Equatorial 705 km, Sun-synchronous

Inclination crossing Inclination=98.2 10:00 am.±15 min

Launch April 15, 1999

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images were generated (Figs. 3 & 4). Contraststretching is performed to stretch the range ofdisplay, so that the contrast of the image will beimproved. In contrast stretching, histogram equal-ization of FCC (4, 3, 2) is generated (Fig. 5).Principle Component Analysis (PCA) had provenvalid process in the analysis of multispectral andhyperspectral remotely sensed data (Zhao andMaclean 2000, Mitternicht and Zinck 2003). PCAfor the study area has been carried out to differen-tiate the anorthosite from other rock types.

Spectral Analysis

Spectral analysis was carried out by obtaining spectralprofile from satellite data for selected locations. In aspectral profile, the ‘X’ axis devoted for the individualbands in the data set and the ‘Y’ axis documents thepercentage of reflectance or brightness value of the pixelunder investigation for each of the bands. The useful-ness of spectral profile depends upon the quality ofinformation available in the spectral data. The analystoccasionally assumes that in order to do quality remote

Fig. 3 False ColorComposite Image ofSittampundi Anorthositecomplex

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sensing research they need a number of bands. Spectralprofiles can useful in providing unique visual andqualitative information about the spectral characteristicsof the phenomena under investigation.

Spectral profile is plotted from Landsat ETM datafor pure anorthosite pixels, mixed anorthosite pixels(Fig. 6), pink migmatite, hornblende biotite gneiss andgranite. The spectral profile generated for the Sittam-pundi anorthositic complex is compared with the labspectra. Homogeneous spectral profile obtained formost of the pixels selected from anorthosite complex.

The percentage of image spectral reflectance is variedfrom 30% to 60%. The bands 2, 4 and 6 with spectralrange of 525 nm–605 nm, 750 nm–900 nm and10400 nm–12500 nm respectively provide the lowreflectance. Bands 3 and 5 with spectral range of630 nm–690 nm and 1550 nm–1750 nm respectivelyshow high reflectance. The comparative results of imagespectra with field and lab spectra are shown in theTable 2. The spectral characteristics of field and labspectra were taken from the previous study (Anbazhaganand Arivazhagan 2010).

Fig. 4 TrueColor Compositeimage of SittampundiAnorthosite complex

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Discussion

The purpose of the study is to understand the remotesensing characteristics of the Sittampundi anorthositecomplex, which is considered as equivalent of lunarhighland region. Image analysis was carried out toknow the spectral behaviour of anorthositic complex.The chemical compositions and arrangement ofminerals in a rock control the shape of spectral curveand absorption bands at different portion of the electromagnetic spectrum. The diagnostic characteristic ofspectral curve and absorption band position is usefulin identifying the minerals and rocks. However, rocksare aggregates of minerals and compositionally morecomplex than minerals. Hence determining the diag-

nostic features of the rock spectra is difficult.However, it is possible to describe the spectralcharacteristics of rock based on its constituentminerals.

The Sittampundi anorthosite complex is dominatedby relatively pure calcic—anorthite (An82) and labra-dorite. The accessory minerals are pyroxene, horn-blende and biotite. The mineralogy of lunar anorthositemostly comprises plagioclase feldspar, Ca-pyroxeneincluding ortho pyroxene and pigeonite. The probablediagnostic absorption features in the anorthosites areFe2+ and Fe3+ intervalance charge transfer absorptionsnear 770 nm (Cloutis 2002), pyroxene absorptionbands near 1000 nm and 2000 nm (Adams 1974),olivine multiple component absorption at 1050 nm

Fig. 5 Histogram equaliza-tion image of SittampundiAnorthosite complex

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(Crown and Pieters 1987), weak absorption at1250 nm–1300 nm due to plagioclase feldspar with>1% of FeO (Adams and Goulland 1978; Bell andMao 1973; Cheek et al. 2009).

The field reflectance spectra of anorthosites haveshown weak absorptions at 650 nm, 750 nm and950 nm (Arivazhagan et al. 2009). In Sittampundianorthosite, the presence of ferrous iron in pyroxenemay give rise to Fe2+–Fe3+ intervalance chargetransfer absorption bands near 650 nm and 750 nm.The reflectance spectra do not show a prominentabsorption features in these bands probably due tolow Fe3+ content. The low Ca- pyroxene also givesweak absorption band at 950 nm. In the presentcontext, digitally processed satellite data outputs weregenerated mainly to optimize the suitable image

processing technique to delineate the terrestrialanorthosite complex. So that similar procedure andtechnique may be adopted for mapping the lunarhighland region. Further, the image analysis facilitatesto compare the image spectra with the reflectancespectra obtained from the ground measurements.Though the Sittampundi anorthosite complex isconsidered as analog test site for lunar highlandregion in terms of chemistry and mineralogy, theweathering and presence of hydroxyl content in thisterrestrial anorthosite may provide slightly differentreflectance spectra. The absorptions due to Al–OHand Mg–OH in terrestrial anorthosites show absorptiondoublets at 2200 nm and 2330 nm (Anbazhagan andArivazhagan 2010), which may not be prominentlyshown in the lunar anorthosite spectra.

Fig. 6 Spectral profile of the pure and mixed anorthosite pixels

Table 2 Comparison of image spectra, with field and lab spectra

Image spectra Field spectra under 350 nm–2500 nma Lab Spectra under 350 nm–2500 nma

Band number and spectralrange in μm

Reflectance (%)

1 (0.45–0.52) 45

2 (0.52–0.61) 40

3 (0.63–0.69) 45 Weak absorption (700 nm)

4 (0.75–0.90) 30 Weak absorption (1398 nm) Weak absorption (700 nm)

5 (1.55–1.75) 60 Weak absorption (1833 nm) Weak absorption (1406 nm)

6 (10.4–12.5) 35 Strong absorption (1913 nm) Strong absorption (1914 nm)

7 (2.09–2.35) 50 Strong absorption (2122 nm) Strong absorption (2200 nm)

a Anbazhagan and Arivazhagan (2010)

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The True Color Composite generated using thebands 3,2 &1 in red, green, blue filters has givencontrast signature for anorthosite has bluish whitecolor. The False Color Composite generated with 4, 3& 2 bands shows similar contrast for anorthosite andenhanced output for pink migmatite. The bandcombination with 1,2 & 3 bands under red, green,blue filters is given excellent output for anorthositecomplex. In addition, the other rock types such aspink migmatite, hornblende biotite gneiss are clearlydistinguishable. Out of various processed outputs,histogram equalization of band 4,3 & 2 has givenbetter contrast for anorthosites, pink migmatite,hornblende biotite gneiss and granite. The PCAanalysis is useful in enhancing the spectral signatureof anorthosite, pink migmatite and gneissic rocks. Thefield and lab spectra obtained for anorthosites in theprevious study were compared with image spectra(Table 2). In which the spectral range of bands 4 & 7with 750 nm–900 nm& 2090 nm - 2350 nm respectivelyshow low reflectance (absorption) and matching withfield and lab spectra.

Conclusion

Sittampundi anorthosite complex is considered asterrestrial equivalent of lunar highland region. Imageanalysis was carried out to delineate anorthositecomplex and understand the spectral behavior ofanorthosite. The image analysis with band combina-tion of 231, PCA and Histogram equalization areprovided quality information on anorthositic complex.The spectral profile obtained from Landsat ETM datais compared with the field and lab reflectance spectra ofSittampundi anorthosite complex. The low percentageof reflectance for bands 4 and 7 were compared with thefield spectra. The image analysis and spectral compar-ison of Sittampundi anorthosite complex are useful forremote sensing study of lunar highland region. Probablyanalysis of hyperspectral image for Sittampundi anor-thosite with narrow bandwidth will be more useful forremotely study the similar terrain.

Acknowledgement The authors acknowledge Physical ResearchLaboratory, Ahmedabad for provided funding through PLANEXprogramme. The second author acknowledges Tamil Nadu StateCouncil for Science and Technology, Chennai for providingfinancial assistance to her dissertation work. The corresponding

author acknowledges the CSIR, New Delhi for providing SRFfellowship.

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