generation of emissivity and land surface temperature maps using modis tir data for lithological...

0016-7622/2012-80-5-685/$ 1.00 © GEOL. SOC. INDIA

JOURNAL GEOLOGICAL SOCIETY OF INDIAVol.80, November 2012, pp.685-699

Generation of Emissivity and Land Surface Temperature MapsUsing MODIS TIR Data for Lithological Mapping over

the Singhbhum-Orissa Craton

T. J. MAJUMDAR1*, S. K. PAL

2 and AMIT K. BHATTACHARYA3

1Space Applications Centre (ISRO), Ahmedabad – 380 0152Department of Applied Geophysics, Indian School of Mines, Dhanbad – 826 004

3Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur – 721 302Email: [email protected]

Abstract: The present study was undertaken with four fold objectives, namely, (i) to estimate land surface temperatureusing MODIS TIR data; (ii) to calculate relative emissivities from MODIS TIR data; (iii) to identify various lithologiesbased on relative emissivity and land surface temperature estimation; and finally, (iv) to carry out comparative assessmentanalysis between the prepared lithological map and the published lithological map. The land surface temperatures fordifferent pixels were estimated using two methods, viz., Reference Channel and Emissivity Normalization; whereas,relative emissivities were calculated by applying three methods, viz., Reference Channel, Emissivity Normalization andAlpha Residual. Lithological maps were subsequently prepared based on the estimated land surface temperatures andrelative emissivity values. The present study shows that the Emissivity Normalization method gives the best results forland surface temperature estimation and also for lithological discrimination based on emissivity estimation. Twenty-fourlithounits demarcated by the present study match with those of the published map, while four lithounits of the publishedmap could not be identified in the present study. On the other hand, six additional unclassified lithounits could bedemarcated in the present study, which need to be crosschecked by field study.

Keywords: MODIS, Emissivity, Lithological mapping, Singhbhum-Orissa craton.

while it itself, in turn, controls most of the physical, chemicaland biological processes of the earth (Becker and Li, 1990).Variations in spectral emissivity are particularly useful forgeological mapping since these relate to differences incompositions (Lyon, 1965). Thus, geological studies aremore concerned with emissivity variations that provide ameans of lithological mapping and less concerned withtemperature. However, surface temperature effects that masksubtle variations in emissivity dominate the measuredradiance. This leads to the developments of a variety oftechniques for lithological discrimination, which eitherenhance or separate the emissivity from the temperatureeffects. Number of scientists (Becker, 1987; Kahle, 1987;Kealy and Hook, 1993; Wan and Dozier, 1996; Wan andSnyder, 1996; Wan and Li, 1997; Gillespie et al. 1998; Liang,2001; Dash et al. 2002; Wan et al. 2002; Sobrino et al. 2003;Wan et al. 2004) have worked extensively for developingtechniques for extracting LST and emissivity values, whichare derived from radiance data separation in TIR regions.Some of these techniques are: the Reference Channel

INTRODUCTION

The measured radiance from the earth surface in thethermal infrared region is a function of both emissivity andtemperature information. Emissivity calculations andsubsequent estimation of land surface temperature (LST)using MODIS thermal infrared (TIR) bands have openedup new possibilities for satellite based lithological mapping,as emissivity is controlled by the composition of the surfacerock and is often used for constituent/lithological mapping.In this context, silicate minerals play important roles, asemissivity characteristics of silicate minerals are found tobe useful indicators of lithology. In the present study, theterm ‘relative emissivity / emittance’ is more relevant than‘absolute emissivity’, as it is related to measurement ofnatural surface rather than ideal specimen. LST is known tobe one of the key diagnostic parameters of the physicalprocesses of land surface, involving both surface andsubsurface geology (Becker and Li, 1990). LST is controlledby surface energy balance, atmospheric condition, andthermal properties of surface and subsurface formation;

JOUR.GEOL.SOC.INDIA, VOL.80, NOV. 2012

686 T. J. MAJUMDAR AND OTHER

method, the Emissivity Normalization method, theTemperature-Independent Spectral Indices method, theSpectral Ratio method, and the Alpha Emissivity (AlphaDerived Emissivity/Alpha Residual) method (Li et al. 1999).However, this study assesses the performances of threetechniques, viz., the Reference Channel method, theEmissivity Normalization method and the Alpha Emissivity(Alpha Derived Emissivity/ Alpha Residual) method usingModerate Resolution Imaging Spectrometer (MODIS) data.

MODIS is an earth-viewing sensor that is mounted onthe Earth Observing Systems, namely, Terra and Aquasatellites, which were launched in 1999 and 2002respectively. MODIS has a swath of 2330 km (cross-track)by 10 km (along-track at nadir). It scans the earth from apolar orbiting sun-synchronous platform at an altitude of705 km. MODIS provides multispectral image in thirty six(36) spectral bands ranging between 0.415 µm (visible) to14.235 µm (thermal infrared) with spatial resolutions of250m (first two bands), 500m (next five bands) and 1 km(remaining twenty nine bands). Details of MODIS bandspecifications are available at https://lpdaac.usgs.gov/products/modis_products_table.

GEOLOGICAL SETTING OF THE STUDY AREA

The present study area lies between latitudes 20°50' Nand 23°24' N and longitudes 84°56' E and 87°5' E, coveringparts of Jharkhand, West Bengal and Orissa States of India.This area constitutes geologically one of the most complexand mineralogically rich belts of the Indian subcontinent.The area has been extensively studied by various geologists(Dunn, 1929; Sarkar and Saha, 1963; Naha, 1965; Sarkarand Chakraborty, 1982; Saha, 1994) using ground basedconventional geological methods. The area has a majortectonic element, known as Singhbhum shear zone (SSZ)that separates the cratonic block (Singhbhum-Orissa craton)in the south from the Proterozoic mobile belt (Singhbhummobile belt) in the north. The SSZ runs as a northwarddipping zone along a northwardly convex arcuate belt oflength about 160 km from Bhaharagora in the east toChakradharpur in the west. Various rocks of the study areahave undergone several phases of deformation andmetamorphism. Rocks south of the Singhbhum shear zoneare relatively less metamorphosed compared to those in thenorth. Rocks of Older Metamorphic Group (OMG) formthe basement rocks. They are exposed in the central part ofthe basin. OMG mainly consists of schist. The Iron OreGroup (IOG) rocks overlie the basement rocks and areexposed over vast areas in the western part and to someextent in the eastern part. The IOG succession is believed

to have formed a broad NNE plunging synclinorium withoverturned western limb. The published geological map(Fig. 1) of the study area (after Saha, 1994), prepared byconventional geological mapping method shows theoccurrence of twenty eight lithologies.

DATA USED

In order to extract emissivity and subsequent estimationof LST, suitable TIR bands of MODIS data have to be used.For atmospheric transmission (Wan, 1999) at viewing angleof 45° from nadir in mid-latitude summer condition (i.e.column water vapor (cwv) = 2.9 cm and surface visibilityat 0.55 µm (vis.) = 23 km, bands 20, 22, and 23 are recordedin the 3.5 - 4.2 µm range, while bands 29 to 32 are recordedin the 8 -13 µm range. All these are within the atmosphericwindow. However, bands 33 to 36 (13.34 - 14.24 µm) arerecorded at the edge of this atmospheric window. Theatmospheric transmission in band 33 is very low (lowerthan 0.35 in many cases) under different atmosphericconditions (Liang, 2001); while band 30 is strongly affectedby ozone absorption. Hence, retrieval of LST using thisband (30) is not very effective. Major absorbers in bands20, 22, and 23 are CO2, N2 and water vapor while majorabsorbers in bands 29 and 31-33 are water vapor and CO2

(Wan, 1999). The atmospheric transmission correspondingto aerosol scat-tering and absorption in these bands isapproximately within the range 0.95-0.98. Therefore, TIRbands 20, 22, 23, 29, and 31 to 33 can be used for retrievingsurface emissivity and temperature (Wan and Snyder, 1996;Wan, 1999).

MODIS (Level 1B) bands, 20-36 of MOD021KM ofMay 7, 2003 have been chosen for this study. ThisMOD021KM contains calibrated radiances generated fromMODIS Level 1A scan of raw radiance. MODIS technicalspecifications are available at https://lpdaac.usgs.gov/products/modis_products_table.

Remotely sensed images include information about theatmosphere as well as information about the surface. Forquantitative analysis of surface reflectance, removal of theinfluence of the atmosphere is important. To compensatefor atmospheric effects, properties such as the amount ofwater vapor, distribution of aerosols, and scene visibilitymust be known. Because direct measurements of theseatmospheric properties are rarely available, there aretechniques that infer them from their imprint on hyper-spectral radiance data. These properties are then used toconstrain highly accurate models of atmospheric radiationtransfer to produce an estimate of the true surface reflectance(Adler-Golden et al. 1999).


EMISSIVITY AND SURFACE TEMPERATURE ESTIMATION OVER SINGHBHUM 687

Fig.1. Geological map of the study area (after Saha, 1994). 1-Older Metamorphic Group; 2-Older Metamorphic Tonalite-gneiss; 3-PalaLahara Gneiss; 4-Singhbhum Granite-Phase-I; 5-Singhbhum Granite-Phase-II and xenolith-dominated areas of Bonai Granite;6-Nilgiri Granite; 7-Iron Ore Group lavas, ultramafics; 8-Iron Ore Group shales, tuffs, phyllites; 9-BHJ, BHQ and sandstone-conglomerate of Iron Ore Group; 10-Singhbhum Granite –Phase-III, Bonai Granite, Chakradharpur Granite; 11(a)-SinghbhumGroup pelites, 11(b)-mafic bodies 11(c)-carbon phyllite; 12-Singhbhum Group quartzites; 13-Dhanjori Group(unclassified); 14-Quarzite-conglomerate-pelite of Dhanjori Group; 15-Dhanjari-Simlipal-Jagannathpur-Malangtoli lavas; 16-Dalma Lavas; 17-Proterozoic Gabbro-anorthosite-ultramafics; 18-Kolhan Group and equivalents 19-Mayurbanj Granite; 20-Soda granite, ArkasaniGranite, Kuilapal Granite, alkaline granite; 21-Charnockite; 22-Khondalite; 23-Amphibolite enclaves (within CGG) 24-peliticenclaves within CGG; 25-Chhotanagpur granite-gneiss(CGG); 26-Porphyritic member of CGG; 27-Gondwana sediments 28-Alluvium, Tertiaries.



METHODOLOGY

It is well established that spectral emissivitycharacteristics for the terrestrial land cover types arerelatively stable (least variation of emissivity), in thewavelength range 10.5 to 12.5 µm, which are covered bybands 31 and 32 of MODIS (Wan and Dozier, 1996).Salisbury and D’Aria (1992) have recorded spectralreflectance values of eighty (80) terrestrial material samples,which include igneous, metamorphic and sedimentary freshrocks, varnished rock surfaces, soil, green foliage, water,ice and oil slicks. Wan (1999) has shown that constantemissivity approximations within the range of 0.97 to 0.99in bands 31 and 32 are observed quite good for all naturalland cover types except for exposed rocks and sands.However, according to Kealy and Hook (1993), most of thegeological earth surfaces have an emissivity of about 0.96.Accordingly, the present study has been carried out withtwo constant emissivitiy approximations of 0.96 and 0.98for both band 31 and 32 independently. Wan and Snyder(1996) and Wan (1999) have shown that the bandemissivities in MODIS bands 31 and 32 are relatively stable.

In Planck’s equation, the spectral radiance of a blackbody at temperature T can be written as,

]1)[exp( 25

1

−=

T

CC

L

jj

BBij

λπλ

(1)

where LijBB is black body radiance (Wm-3), i is the pixel no.

of band j, T is the temperature of black body (K), λj iswavelength of band j (in µm), first radiance constant, C1 is3.74151 x 10-16(Wm2), and second radiance constant, C2 is0.0143879 (mK). The spectral emissivity (εij) of a material,in band j for pixel i, is defined as the ratio of the radiance ofthat material (Lij) to that of a blackbody (Lij

BB) at the sametemperature as the material, which can be mathematicallyexpressed as,

BBij

ijij L

L=ε or BBijijij LL ε= (2)

The emissivity spectra over various lithounits can beextracted to evaluate effectiveness of different methods ingeological studies, since lithological discriminations aredependent on the positions and depths of minima andmaxima in the spectrum.

Reference Channel Method

The Reference Channel method assumes that all the

pixels of a specific band of the thermal infrared data have aconstant emissivity value (Kahle et al. 1980). On thisassumption, in the present study, bands 31 and 32 of MODISdata are used with constant emissivity of 0.96 and 0.98,separately to calculate LST and band relative emissivity.Once the emissivity for a Reference Channel is assumed,the temperature T can be calculated for that band using thefollowing equation (Kealy and Hook, 1993):

]1ln[51

2

+=

πλελ

RR

RR

R

L

CC

T (3)

where, subscript ‘R’ denotes the particular ReferenceChannel, and LR is the radiance at that band. Thistemperature information can then be used to calculate theemissivity values for all other bands using equations (1)and (2).

Emissivity Normalization Method

This method is similar to the Reference Channel method(Gillespie, 1985) with a little difference. In this method,the temperature is calculated for every pixel in each bandusing constant emissivity value (e.g. 0.96 or 0.98 separately).The highest of these temperatures at each pixel in differentbands is defined as the temperature of that pixel. Thustemperature image for the entire study area is calculated.This temperature information is then used to calculate theemissivity values using equations (1) and (2).

Alpha Residual Method

This method makes use of Wien’s approximation ofPlanck’s equation, which is given as,

)][exp( 25

1

ijj

BBij

T

CC

L

λπλ

= (4)

In Wien’s approximation of Planck’s equation, the ‘-1’term, in the denominator, is neglected so that the equationcan be linearized with logarithm. The Alpha Residual methodis a two-step procedure: (i) initially, natural logarithms areformed from the Wien’s approximation of Planck’s equationand subsequently wavelength weighted logarithm of Wienradiance at pixel i in band j (Xij) is generated in order toseparate λ and T ; (ii) the geometric mean over all bandsfor pixel j (Xij) is then subtracted from the wave-length weighted log of Wien radiance at pixel i inband j (Xij). The procedure is discussed in details elsewhere



(Hook et al. 1992). Brief mathematical procedure is asfollows:

(5)

Finally, alpha residual, αij, is obtained as given below:

j

n

jijjijjiJijij K

nXX +−=−= ∑

=1

ln1

ln ελελα

(6)where,

From equation (6), it is clear that Kj is not a function ofmeasured radiance but wavelength dependent constant only,which can be calculated for each band. Thus, the AlphaResidual spectrum is a function of emissivity only. Kealyand Hook (1993) have shown that the Alpha Residual spectraare similar in shape as emissivity spectrum, but have zeromean. They also concluded that the Alpha Residual spectrumcould be of great help in geological studies since thelithological discriminations are dependent on the positionsand depths of minima and maxima in the spectrum.

RESULTS

Reference Channel Method

Emissivity values and LST over the study area arecalculated assuming constant emissivities of bands 31 and32 (as stable bands) for different band combinations, viz.,(i) 20-33 (i.e., 20, 22, 23, 29, 31, 32 and 33), and (ii) 29-33(i.e., 29, 31, 32 and 33) of MODIS data using ReferenceChannel method. Besides these LST estimations over thestudy area, ambient temperatures have been collected fromdifferent available weather stations of Indian MeteorologyDepartment close to the study area (Table 1, All IndiaWeather Bulletin, 2003). These stations are: Kolkata,Jamshedpur, Ranchi, Gaya, Patna and Bhubaneswar. Thetemperatures recorded from these stations provided acomparison of the temperatures estimated by variousmethods followed in the present study. Tables 2a and b showthe estimated temperatures using Reference Channel method,for different band combinations assuming 0.96 and 0.98emissivity values for bands 31 and 32 respectively, along

with the recorded maximum and minimum temperatures.The fact that MODIS data acquisition over the study areahas been at 10.30 A.M., the estimated LST using the methodsadopted in the present study will be slightly higher than themean of minimum and maximum recorded temperatures atdifferent weather stations; this fact should be taken intoaccount for assessment of estimated LST results (Majumdarand Bhattacharya, 1988).

Histograms of LST over the study area using ReferenceChannel method are shown in Fig. 2a for comparative studyand comprehensive assessment of LST calculations. Thus,from Tables 2 a and b and Fig. 2a, it can be said that LST,calculated using band combination 29-33 with emissivityvalue 0.98 for band 31 (henceforth, denoted as 2933-98-31) generates a temperature closer to the observedtemperature. Moreover, LST calculation, with the constantemissivity 0.98, is more accurate in Reference Channelmethod than that of the constant emissivity 0.96. Further,

ijBB

ijij LL ε lnlnln =+=

ijjij T

CC λπλε 21 lnln5lnln −−−+=

Table 1. All India Weather Bulletin (dated 08.05.2003)

Station Latitude Longitude Temperature (°C)

Max. Min. Mean

Patna 25.35°N 85.12°E 40 22 31Gaya 24.47°N 85.04°E 41 24 32.5Ranchi 23.19°N 85.27°E 38 22 30Jamshedpur 22.40°N 86.12°E 43 26 34.5Kolkata 22.36°N 88.24°E 35 18 26.5Bhubaneswar 20.15°N 85.50°E 39 28 33.5

Table 2. Comparative study of LST calculation using Reference ChannelMethod with the stable band (a) 31, (b) 32 and (c) Normalizationmethod with constant emissivities 0.96 and 0.98 for differentband combinations for different band combination

(a) Reference Channel method with constant emissivity for band 31

Station 20_33_98_31 20_33_96_31 29_33_96_31 29_33_98_31Patna 41.69 42.24 39.24 37.69Gaya 36.49 41.98 37.98 35.58Ranchi 37.58 42.13 38.13 34.39Jamshedpur 39.93 43.48 41.48 38.93Kolkata 32.70 26.09 29.09 26.7Bhubaneswar 41.98 40.45 36.45 32.98

(b) Reference Channel method with constant emissivity for band 32

Station 20_33_98_32 20_33_96_32 29_33_96_32 29_33_98_32Patna 43.31 42.00 45 38.31Gaya 40.74 34.33 34.33 36.74Ranchi 42.88 41.56 41.56 37.88Jamshedpur 43.48 43.15 42.15 41.48Kolkata 23.80 25.30 25.3 23.80Bhubaneswar 40.50 32.06 32.06 30.50

(c) Normalization method

Station 20_33_98 20_33_96 29_33_96 29_33_98 Patna 43.76 42.34 38 34.31Gaya 43.67 44.26 36.98 35.49Ranchi 40.83 42.40 34.56 32.88Jamshedpur 45.69 45.26 37.48 36.93Kolkata 38.33 40.87 26.09 25.70

Bhubaneswar 41.27 45.83 34.45 32.98

−−−= jjjjj CK 1

lnlnln5ln πλλλλ

∑∑∑===

++n

jj

n

jjj

n

jj nnn

C

111

1 lnln

5ln λπλλλ



bands 29 and 31-33, which are in the 8-13 µm atmosphericwindow are more suitable for LST calculation usingReference Channel method, than that of the bands 20, 22,and 23, which are in the atmospheric window in the 3.5-4.2 µm medium wavelength range. Temperatures observedin bands 20, 22, and 23 are higher than the expected LSTover the area. Detail statistics of calculated LST usingdifferent technique are enlisted in Table 3. LST (Min =24.59°C, Max = 39.16°C, Mean = 29.40°C, Std. dev =3.23°C) calculated using Reference Channel method fromthe bands 29, 31, 32 and 33 with constant emissivity 0.98for the band 31, is shown in Fig.3. An approach has beenmade to discriminate different lithological boundary as perLST and the inferred lithological boundary map (vectorcoverage) has been overlaid on it.

Emissivitiy spectrum is extracted from band emittances(emissivities) 20, 22, 23, 29, 31, 32 and 33 assumingconstant emissivity values of 0.96 and 0.98, in separate casesfor the stable band 31 and 32, (denoted as Ref_20_33_96_31, Ref_20_33_98_31, Ref_20_33_96_32 andRef_20_33_98_32, respectively). Further relative emissivityspectra have been collected from ten major distinct lithounits(1. Iron Ore Group, 2. Chhotanagpur Granite-Gneiss, 3.

Dalma Lavas, 4. Dhanjori-Simlipal-Jagannathpur-Malangtoli Lavas, 5. Singhbhum Granite, 6. Alluvium, 7.Alluvium/Gondwana Sediments, 8. Nilgiri Granite,9. Singhbhum Group Pelites and 10. Granite/Bonigranite,refer Fig.1) for applicability to demarcate lithology overthe area, separately for four sets of band emittances(emissivities). However, out of the four, the spectrumRef_20-33_96_31 (Fig.4a) has more lithologicaldistinguishing capability. In the band emissivities, emissivitycalculated using constant emissivity value 0.96 with thestable band 31 is considered for demarcation of differentlithounits (Kealy and Hook, 1993). In multispectral image,contiguous bands have very little tonal and textural variation,therefore, bands are selected for generation of FCC images,

(a)

(b)

Fig.2. Histograms of LST over the study area for variouscombinations using (a) Reference Channel method, and(b) Emissivity Normalization method.

0C

0C

0C

0C

0C

28

28

30

10

25 25 25

15

15

5

2

8

16

34

27 22

10

11

11

12

19 6

19

31

33

15 35

26 24

19

3

11

16

21 8

9

9

Fig.3. LST calculated using Reference Channel method from bands29, 31, 32 and 33 assuming constant emissivity 0.98 forthe stable band 31. Inferred lithounits over the study areaare traced out as shown in this figure. Serial numbers 1 to28 represent similar lithologies as those of Fig. 1. Serialnumbers 30-35 are unclassified A,B,C,D,E,F.

Table 3. Statistics of calculated LSTs using different techniques

Temperature calculation Min Max Mean Stdevmethods °C °C °C

ref_20_33_31_96_T 27.009521 48.787323 38.7895383.301411

ref_20_33_31_98_T 25.593414 47.167480 37.264544 3.270515

ref_20_33_32_96_T 26.040833 47.446014 38.0092023.464456

ref_20_33_32_98_T 24.516479 45.707733 36.3665003.429800

ref_29_33_31_96_T 27.009521 48.787323 38.7895383.301411

ref_29_33_31_98_T 24.593414 39.167480 29.4038143.237075

ref_29_33_32_96_T 26.040833 47.446014 38.0092023.464456

ref_29_33_32_98_T 24.516479 45.707733 36.3665003.429800

nor_29_31_33_96_T 27.009521 48.787323 38.8016843.306163

nor_29_31_33_98_T 22.793414 36.932480 25.4033613.237217

nor_2022232931_33_96_T 32.408447 67.764740 49.0407704.835214

nor_2022232931_33_98_T 31.901428 67.058929 48.4773154.818213



so that the interband relative emissivity difference andstandard deviation are maximum for easy demarcation ofdifferent lithounits based on tonal and textural variationsover surroundings. Figure 5a shows histogram of relativeemissivity of seven bands (20-33) calculated using ReferenceChannel method assuming constant emissivity 0.96 for band31. Figure 5b shows plot of minimum, maximum, and meanof band emissivities. The detailed statistics of band emittanceare listed in Table 4 a. Bands 23, 20 and 33 have been chosento generate FCC image (Fig. 5c) for delineation of variouslithounits based on the Figs. 5a and b, and Table 4a, so thatthe interband relative emissivity difference and standarddeviation are maximum.

Emissivity Normalization Method

Emissivity values and LST over the study area have also

been calculated assuming constant emissivities, 0.96 and0.98, in separate cases for different band combinations,viz., (i) 20-33 (i.e., 20, 22, 23, 29, 31, 32 and 33), and(ii) 29-33 (i.e., 29, 31, 32 and 33) of data using EmissivityNormalization method.

Histograms of LST over the study area usingNormalization method are shown in Fig.2b for comparativestudy and comprehensive assessment of LST calculationusing different methods. Table 2c shows a comparativestudy of LST calculation using Normalization methodassuming constant emissivities for different bandcombinations. Analyses of Fig. 2b and Table 2c indicatethat LST calculation using Normalization method with bandcombination 29-33 assuming constant emissivity 0.98provides closer LST (Table 1, All India Weather Bulletin,2003) than that by assuming constant emissivity 0.96.

Wavelength(µ m)

Alp

ha r

esid

ual

(c) Alpha_20-33

Wavelength(µ m)

Em

issiv

ity

(b)Nor_20-33_96

Wavelength(µ m)

Em

issiv

ity

(a)Ref_20-33_96_31

Fig.4. Emissivity spectral plots collected from different lithological units (a) obtained from Reference Channel method assuming constantemissivity 0.96 and band 31 as stable. (b) obtained from Emissivity Normalization method assuming constant emissivity 0.96.(c) obtained from Alpha Residual method. Lithounits: 1.Iron Ore Group, 2.Chhotanagpur Granite-Gneiss, 3.Dalma Lavas,4.Dhanjori-Simlipal-Jagannathpur-Malangtoli Lavas, 5.Singhbhum Granite, 6.Alluvium, 7.Alluvium / Gondwana Sediments,8.Nilgiri Granite, 9.Singhbhum Group Pelites, and 10.Singhbhum Granite/ Bonigranite.



Further, it is also observed that the LST obtained usingNormalization method is more appropriate than that obtainedusing Reference Channel Method. Detailed statistics ofgenerated LST using different technique are enlisted inTable 3. The LST (Min= 22.790C, Max= 36.930C, Mean=25.400C, Std dev= 3.230C) calculated using emissivitynormalization method from the bands 29, 31, 32 & 33assuming constant emissivity 0.98 is shown in Fig. 6.Inferred lithounits are similar to them as observed in Fig. 1,as mentioned in Fig. 6.

Emissivitiy spectra are extracted from band emittanceof the bands 20-33 using constant emissivity values 0.96and 0.98, (denoted as Nor_20-33_96 and Nor_20-33_98,respectively). However, out of the two, the spectrumNor_20-33_96 (Fig.4b) has more lithological distinguishingcapability. The band emittances (emissivities) estimated byconstant emissivity value 0.96 (Kealy and Hook, 1993) hasbeen considered for demarcation of different lithounits.Histograms of relative emissivity of seven bands (20-33)derived using Emissivity Normalization method with

constant emissivity 0.96, and plots of minimum, maximumand mean of band emissivities have been generated, similarin the line of Figs.5a and b used for Reference Channelmethod. The detailed statistics of band emitance are listedin Table 4b. Bands 32, 23 and 33 have been chosen togenerate FCC image (Fig. 7a) for delineation of variouslithounits, after a careful study of the generated histogramand plots of maximum and minimum emissivities. AnotherFCC image (Fig. 7b), generated by selecting bands 29, 32and 31 from band combination 29, 31, 32 and 33, assumingconstant emissivity 0.98, has been found to be suitable indiscriminating four broad lithologies, namely, (I) Alluviumfan/sediments, (II) Dhanjari-Simlipal-Jagannathpur-Malangtoli lavas (III) Singhbhum-Niligiri-Bonai-Chakradharpur granites etc (IV) Singhbhum group pelites/metamorphosed argillaceous rock/ Chhotanagpur granite-gneiss (CGG).

Alpha Residual Method

A spectrum (Fig. 4c) of alpha derived (equation-5) band

Fre

qu

en

cy

Relative emissivity

(a)

(b) Wavelength (µ m)

Em

issiv

ity

28

28

30

10

25 25

25

15

15 5

2

8

16

27

22

10

11

11

12

19 6

19

31

33

15 35

26 24

19

3

11 16

21 8

9

9

18

9

34

Fig.5. (a) Histogram of relative emissivity of seven bands (20-33) using Reference Channel method with constant emissivity 0.96 forband 31. (b) Plot of minimum, maximum and mean of band emissivities. (c) FCC image generated from band emissivities 23, 20and 33 using Reference Channel method (from bands 20,22,23,29,31,32 and 33 for constant emissivity 0.96 for the band 31 asstable). Inferred lithounits over the study area are traced out as shown in this figure. Serial numbers 1 to 28 represent similarlithologies as those of Fig.1. Serial numbers 30-35 are unclassified A,B,C,D,E,F.



emissivities (Alpha Residuals) have been collected fromseven bands, 20, 22, 23, 29, 31, 32 and 33 (denoted asAlpha_20-33) from different lithounits. Histograms of alpharesiduals of seven bands (20-33) have been generated usingAlpha Residual technique as well as plots of minimum,maximum and mean of alpha residual for all seven bands,similar in the line of Figs. 5a and b used for ReferenceChannel method. The detailed statistics of band alpharesiduals are listed in Table 4 c. Bands 32, 20 and 33 havebeen chosen to generate FCC image (Fig. 8) for delineationof various lithounits, based on the assessment of thegenerated histogram and plots of maximum and minimumemissivities and Table 4c; so that the interband AlphaResidual difference and standard deviation are maximum.

DISCUSSION

Reference Channel method has some limitations. First,it assumes the emissivity in one band is constant and hence,spectral information in that band is lost. An incorrectassumption may lead to a decreased or an increased valueof spectrum and also could rotate the spectrum clockwiseor counterclockwise around the assumed stable band,depending upon whether the assumed emissivity value is an

over or underestimate. Further, if the data in the constantband contains noise, this noise is introduced into the otherbands. Likewise, if the data of the stable band is highlycorrelated with the adjacent bands, the data in the adjacentbands will also be forced towards the constant emissivityvalue and the signal to noise ratio between the two bandswill be decreased. On the other hand, Alpha Residualmethod has the disadvantage of assuming initially Wien’sapproximation, although for temperature of 300K and awavelength of 10 µm, the approximation results in less than1% error (Hook et al. 1992).

The relative emissivity spectra as shown in Fig. 4 havebeen collected from ten different lithologies over the studyarea, viz., 1. Iron Ore Group 2. Chhotanagpur granite-gneiss3. Dalma Lavas 4. Dhanjori-Simlipal-Jagannathpur-Malangtoli Lavas 5. Singhbhum Granite 6. Alluvium 7.Alluvium/Gondwana Sediments 8. Nilgiri Granite 9.Singhbhum Group pelites 10. Singhbhum Granite/Bonigranite. Most of the spectra have two strong emissionminima, near 9 µm and 12 µm. The strong broad emissionminimum near 9 µm would be due to presence of clayminerals whereas, the strong emission minimum near 12µm would be due to bending modes involving the carbonateion occurrences (Salisbury et al. 1987). Further, oneweak emission minimum near 11 µm would be due to Si-Ostretching in the silicate lattice, which is generally referred

Table 4. Band-wise statistics of calculated relative emissivities using (a)Reference Channel method (b) Normalization method (c) AlphaResidual method

(a) Reference Channel methodBand Min Max Mean Stdev20 0.339658 0.9956547 0.506918 0.35698522 0.389469 0.984326 0.497243 0.32213223 0.365449 0.9836335 0.416184 0.26076529 0.785645 0.9758229 0.859302 0.38715631 0.859999 0.960001 0.914099 0.41904532 0.778927 0.971430 0.857972 0.41553233 0.486170 0.776168 0.579503 0.282247

(b) Normalization methodBand Min Max Mean Stdev20 0.459469 0.960001 0.713656 0.41903322 0.336292 0.960000 0.626716 0.36877023 0.258977 0.897632 0.529700 0.31248329 0.374180 0.832647 0.546665 0.32195631 0.485807 0.904849 0.616616 0.36286032 0.480991 0.904395 0.618256 0.36393133 0.374519 0.665441 0.423605 0.249541

(c) Alpha Residual methodBand Min Max Mean Stdev20 1.334053 6.291672 1.549069 0.93854022 0.826103 5.102219 1.158558 0.71428223 0.278305 4.349609 0.637763 0.41177429 -2.743373 -0.037990 -0.265211 0.19362631 -2.062538 0.729897 0.265561 0.23018332 -2.730057 0.781525 0.226415 0.26829433 -7.244583 -3.357956 -3.572163 2.127594

0C

35 0C

0C

0C

0C

28

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27 22

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26 24

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9

Fig.6. LST calculated using Emissivity Normalization method fromthe bands 29, 31, 32and 33 assuming constant emissivity0.98. Inferred lithounits over the study area are traced outas shown in this figure. Serial numbers 1 to 28 representsimilar lithologies as those of Fig.1. Serial numbers 30-35are unclassified A,B,C,D,E,F.



as Reststrahlen band (Hunt, 1980). The Reststrahlen bandprovides a means for identifying silicate rocks, as it migratesto longer wavelengths as the material becomes more maficwith decreasing silica and increasing ferromagnesiumminerals (Hunt, 1980; Salisbury et al. 1988). As MODISTIR data have very poor spatial resolution (~1 km) and alsolow spectral resolution, spectra collected over the lithologiesare not pure. The potential pitfalls would be due to slightvariations in mineral composition, mineral admixture,degree of weathering and some uncertainties in sensorcalibration and atmospheric correction, which lead to thepresence of some artifacts and may create difficulty incorrelating the collected spectra with the available libraryspectra. Therefore, the spectral classification techniquesbased on the spectral values of the extracted emissivityimages, would not be effective for discriminating the variouslithologies.

Hence, in the present study, the different lithounitshave been demarcated on the basis of tonal and texturalvariations, textural association and color contrast in thedifferent FCCs, generated from LST and emissivity imagesand corroborated with the published lithological map(Saha, 1994). However, it is clear that the estimated LST

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Fig.7. (a) FCC image generated from band emissivities, 32, 23, and 33 using Emissivity Normalization method (from bands20,22,23,29,31,32 and 33 assuming constant emissivity 0.96). Inferred lithounits over the study area are traced out as shown inthis figure. Serial numbers 1 to 28 represent similar lithologies as those of Fig. 1. Serial numbers 30-35 are unclassified A,B,C,D,E,F.(b) FCC image generated from band emissivities, 29, 32, and 31 using Emissivity Normalization method (from bands 29,31,32and 33 assuming constant emissivity 0.98). Four broad comprehensive areas have been identified: (I) Alluvium fan/sediments,(II) Dhanjari-Simlipal-Jagannathpur-Malangtoli lavas, (III) Singhbhum-Niligiri-Bonai-Chakradharpur granites, and (IV)Singhbhum group pelites / metamorphosed argillaceous rock / Chhotanagpur granite-gneiss.

Fig.8. FCC image generated from alpha residuals, 31, 20, and 33using Alpha Residual method (from bands 20,22,23, 29,31,32 and 33). Inferred lithounits over the study area aretraced out as shown. Serial numbers same as in Fig.7.



are less concerned for discrimination of various lithounitboundaries. Vector topologies for various identifiedlithounits are created to generate closed polygons for alllithounits. The generated vector topologies are overlaid onvarious FCC imageries as shown in Figs. 5c, 7a and 8obtained using Reference Channel method, EmissivityNormalization method and Alpha Residual methodrespectively. It is clear that the Normalization method ismost helpful in discriminating as observed from the relativeemissivity spectra in Figs. 4 a, b and c and the FCC images

in Figs. 5a, 7a and 8. Figure 9 shows the lithological map(henceforth denoted as, MOD-MAP) prepared from the FCC(Fig.7a) of band emitance extracted using EmissivityNormalization method.

Comparative assessment analysis has been carried outbetween the published geological map of Saha (1994) andthe MOD-MAP. Majority of the lithounits, observed in thepublished map (Saha, 1994), have been delineated in theMOD-MAP, as can be seen from Figs. 1, 9 & 10 andTable 5. The result of this comparative assessment analysis

Table 5. Details of geological interpretation and comparative assessment study between present interpreted (MOD-MAP) and publishedlithology maps (Saha, 1994)

SL. Geology/Lithounits Geology of Geology as interpreted Results of comparativeNo. Saha (1994) from present study assessment analysis

(Area, km2) (Area, km2) (Area, km2)

1 Older Metamorphic Group 295.6 88.5 722 Older Metamorphic Tonalite-gneiss 1541.8 983.6 854.53 Pala Lahara Gneiss 1579.7 1872.4 1490.64 Singhbhum Granite-Phase-I 218.5 - -5 Singhbhum Granite-Phase-II and xenolith-dominated

areas of Bonai Granite 1869.4 1285.8 1254.46 Nilgiri Granite 989.2 769.4 674.37 Iron Ore Group lavas, ultramafics 817.5 174.9 165.58 Iron Ore Group shales, tuffs, phyllites 3579.3 4724.6 21339 BHJ, BHQ and sandstone-conglomerate of Iron Ore Group 852.6 700.5 344.8

10 Singhbhum Granite -Phase-III, Bonai Granite,Chakradharpur Granite 8292.4 7099.5 4918.5

11(c) Singhbhum Group pelites 6916.9 3682.8 3573.911(b) Mafic bodis 116.3 - -11(c) Carbon phyllite 40 - -

12 Singhbhum Group quartzites 622.8 416 310.413 Dhanjori Group(unclassified) 3814 Quarzite-conglomerate-pelite of Dhanjori Group 752 161.4 9215 Dhanjari-Simlipal-Jagannathpur-Malangtoli lavas 2963.8 4640.8 285516 Dalma Lavas 1106.4 3006.5 995.617 Proterozoic Gabbro-anorthosite-ultramafics 368 69.5 256.418 Kolhan Group and equivalents 1348.7 497.7 29019 Mayurbanj Granite 1695.5 2438 1513.520 Soda granite, Arkasani Granite, Kuilapal Granite,

alkaline granite 74.7 - -21 Charnockite 174 192 152.622 Khondalite 358.8 325.4 191.823 Amphibolite enclaves (within CGG) 107.8 - -24 Pelitic enclaves within CGG 124.5 129 103.425 Chhotanagpur granite-gneiss(CGG); 4293.5 3488 3438.626 Porphyritic member of CGG 309 311.6 23427 Gondwana sediments 2413 2827.5 2312.728 Alluvium, Tertiaries 6160.6 7194 5940.530 Unclassified (A) 972.7 -31 Unclassified (B) 215 -32 Unclassified (C) 22.5 -33 Unclassified (D) 480 -34 Unclassified (E) 1127.4 -35 Unclassified(F) 123 -36 Total Unclassified area as par the comparative

assessment [29 =30+31 +32 +33+ 34+35+ overlaps 15852of some lithounits]Total 50020 50020 50020



Fig.9. Geological map (MOD-MAP) interpreted from the FCC of band emissivities extracted using Emissivity Normalization method(Fig. 7 a). Serial numbers 1 to 28 represents similar lithologies as those of Fig.1. Serial numbers 30-35 are unclassified A,B,C,D,E,F.

has been highlighted in Fig.10. The total area of the presentstudy is about 50,000 sq km. It is observed that a total areaof about 30,000 sq km (60%) has been identified correctlyin the present study. However, a few prominent areas, suchas, in Fig. 10, A and B within the CGC, C- near Dalma Lava,D and E within the Singhbhum Granite, and F near DhanjoriLava have been demarcated as different unclassifiedlithounits, due to occurrences of color contrasts, tonalvariation and textural variation of these regions from the

surroundings, which do not correlate with the previouspublished geological map of Saha (1994). A total of twentyeight lithounits have been observed in the publishedgeological map (Saha, 1994; Fig.1). On the other hand,although, twenty four lithounits (Fig.9) could be identifiedin the present study, which matches well with the publishedmap, the rest four lithounits could not be delineated fromthe present study due to lack of color, tonal and texturalvariations. These are: Singhbhum 4- Granite - Phase-I, 13-



Fig.10. Geological map represent comparative assessment between the published geological map of Saha (1994) and the MOD-MAP.Serial numbers 1 to 28 represent same lithologies as those of Fig. 1. 29-Change in interpreted geology / unclassified geology asinferred from present study [30-Unclassified-(A); 31-Unclassified-(B); 32-Unclassified-(C); 33-Unclassified-(D); 34-Unclassified-(E) and 35-Unclassified-(F)].

Dhanjori Group (unclassified), 20-Soda Granite, and 23-Amphibolite Enclaves (within CGC).

CONCLUSIONS

From the present study, it can be concluded that the

Emissivity Normalization method using MODIS TIRbands (29, 31, 32 and 33) which lie within the wave-length region 8-13 µm, and assuming constant emissivity0.98, provides best LST estimation. The next best estimationof LST is achieved by Reference Channel methodusing same band combination and assuming constant



emissivity value of 0.98 with band 32 as the stable one.In the preparation of lithological map of the area using

estimated LST and relative emissivity, it is observed thatLST based method is not suitable. On the other hand, theFCC image generated using Emissivity Normalizationmethod, from the band emissivities 32, 23 and 33 selectedfrom band combination 20,22,23,29,31,32 and 33 withconstant emissivity 0.96, is found to be very appropriate indemarcating lithologies over the Singhbhum-Orissa Craton,which agree well with the published lithological map.Moreover, Emissivity Normalization method with the bandcombination 29, 32 and 31 is observed to be suitable indelineating four major features, such as, Alluvium fan/sediments, Dhanjari-Simlipal-Jagannathpur-Malangtolilavas, Singhbhum-Niligiri-Bonai-Chakradharpur granites,Singhbhum Group pelites/ metamorphosed argillaceousrock/Chhotanagpur granite-gneiss), which need to becrosschecked by field study. The next best technique foridentifying lithologies is Reference Channel; FCC imagegenerated using this technique, from the band emissivities,32, 20 and 33, selected from bands 20,22,23,29,31,32and 33 with constant emissivity 0.96 and band 31 as stable,is relatively suitable, whereas, other combinations arenoisy.

Finally, while attempting comparative assessmentanalysis of the two lithological maps, viz., MOD-MAP(inferred lithology) and the published map, it is found thatthere is complete agreement over sixty percent (60%) ofthe study area. Twenty-four lithounits demarcated by thepresent study match with those of the published map, whilefour lithounits of the published map could not be identifiedin the present study. Six additional unclassified lithounitscould be demarcated in the present study, which need to becrosschecked by the field study.

Acknowledgements: The authors wish to thank twoanonymous reviewers for their valuable suggestions forimprovement of the manuscript. They are thankful to ShriA.S. Kiran Kumar, Director, SAC, Ahmedabad and Prof.D.C. Panigrahi, Director, ISM, Dhanbad for their keeninterest in this study. Thanks are also due to Dr. R.Bhattacharya, Oil India Ltd., Guwahati, Dr. P.K. Srivastava,Shri Subhranshu Sanyal, Mr. Sreejith A. P., and Mr.Sabyasachi Maiti, Department of Geology and Geophysics,IIT, Kharagpur for their help at various stages ofdevelopment of this activity. TJM wishes to thank CSIR,New Delhi for Emeritus Scientist Fellowship since January2011.

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(Received: 17 November 2010; Revised form accepted:20 May 2012)

generation of emissivity and land surface temperature maps using modis tir data for lithological...

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