DISTINCT IMAGE FUSION METHODS FOR LANDSLIDE INFORMATION ENHANCEMENT

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1 DISTINCT IMAGE FUSION METHODS FOR LANDSLIDE INFORMATION ENHANCEMENT J.Wang a,b, a *, J.X.Zhang, Z.J.Lu a a Insttute of Photogrammetry & Remote Sensng, CASM, Bejng, Chna - stecsm@publc.bta.net.cn b Department of Envronment & Spatal Informatcs, CUMT, Xuzhou, Chna - wjancumt@63.com KEY WORDS: Image Fuson, landslde, shft nvarant, dscrete wavelet transform ABSTRACT: Image fuson s a basc tool for combnng low spatal resoluton mult-spectral and hgh spatal resoluton panchromatc mages usng advanced mage processng technques. Study on effcent mage fuson method for specfc applcaton s on of the most mportant problems n current remote sensng communty and the comparson of dstnct Image fuson methods s prevalent. However, not much work has been reported about fuson for landslde feature enhancement. The present work s focused on the ntensty-hue-saturaton (IHS) merger, Brovey transform (BT) merger, prncpal component analyss(pca) merger and the proposed new merger based on shft nvarant dscrete wavelet transform(sidwt) theory usng maxmum value selecton rule of approxmaton coeffcents for landslde characterstc enhancement. Here we use the panchromatc (PAN) band and multspectral(ms) bands of the LANDSAT-7 ETM+ at the spatal resolutons of 5m and 3m for experment. Vsual nterpretaton of specfc landslde body show the valdty of the new method and shannon entropy and standard devaton ndexes for synthetcally quanttatve evaluaton of the test magery also show the advantage of the new scheme on mage fuson.. General Instructons. INTRODUCTION Remote sensng s a fundamental tool provdng a relatvely lower cost for the detecton, classfcaton and montorng of landslde phenomena. There are several means that permt the mprovement of mage qualty by fusng panchromatc(pan) band and multspectral(ms) bands. Probably the most popular mage fuson methods are those based on the ntensty-huesaturaton transformaton(ihs), prncpal component analsyss (PCA) and brovey transform (BT). In ths paper, we present a mproved merger based on shft nvarant dscrete wavelet transform theory(i-sidwt) usng maxmum value selecton rule of approxmaton coeffcents, whch s ft for landslde nformaton enhancemnt. We have determned the valdty of each fuson method by quantty evaluaton of the test magery and vsual comparson of landsde body enhancement. 2.2 Standard Brovey Merger The Brovey transform merger uses a mathematcal combnaton of the MS bands and PAN band. Each MS band s multpled by a rato of the PAN band dvded by the sum of the MS bands. The fused Rnew,G new,b new bands are as follows(vrabel,99): R new R G new G B new B = () = (2) = (3) THE POPULAR IMAGE MERGERS Standard IHS Merger To get the fused mage, red, green, and blue (RGB) bands are frstly converted to ntensty, hue, and saturaton (IHS) bands. Then ntensty band whch contan most spatal structures of MS bands s substtuted by the PAN band. Before dong ths, and n order to mnmze the modfcaton of the spectral nformaton of the fused MS bands wth respect to the orgnal MS bands, the hstogram of the PAN band s matched wth that of the ntensty band. Applyng the nverse transform, we obtan the fused RGB mage (Carper,et al.,99; Mara, et al.,24). 2.3 PCA Merger The PCA merger s based on the fact that the frst prncpal component contans the man spatal nformaton of the MS bands, whle the spectral nformaton wth respect to each band s pcked up n the other prncpal components. A prncpal components transformaton s performed on the MS bands. The frst prncpal component s substtuted by the PAN band whose hstogram has prevously been matched wth that of the frst prncpal component, whch s much smlar to the IHS method. Fnally, an nverse transform s performed obtanng the fused mage(welch,et al.,987). * Correspondng author.

2 PAN SIDWT PAN A PAN H F[ ] F A MS H PAN V PAN D MS V MS D ETM+ PAN band Inverse SIDWT MS SIDWT MS A MS H FI ETM+ MS band MS V MS D Fused mage Fgure The block dagram of the SIDWT mage fuson scheme 3. IMPROVED SIDWT MERGER It s well known that the DWT yelds a shft varant sgnal representaton resultng n a shft dependent fuson scheme whle SIDWT mage fuson scheme overcomng the dsadvantages. SIDWT, related to the concept of wavelet frames, was proposed by Unser(Unser,995). Consderng some characterstc of the approxmaton wavelet coeffcents of SIDWT, An approxmaton scale based wavelet coeffcent maxmum selecton rule for mage fuson was presented. For convenence, We frstly summarze the SIDWT for the case of D nput sgnals, then the actual mproved mage fuson methodology(yocky,996). The fast SIDWT was realzed by so-called à trous algorthm by means of upsamplng and downsamplng flters. Each stage of the SIDWT splts the nput sgnal nto the detal coeffcent d (n),and the approxmaton coeffcent c(n) whch serve as nput for the next decomposton level: d ( n) = g(2 k) c ( n k) + k (4) + ( n) = h(2 k) c ( n k (5) k c ) The decomposton start wth c (n)=f(n). The flter g(2 k) and h(2 k) at level are obtaned by nsertng approprate number of zeros between the flter taps of the prototype flters g(k) and h(k). The reconstructon of the nput sgnal s performed by the nverse SIDWT c ( k ) = + n h (2 n g (2 k n ) c + k n ) d ( k ) + ( k ) Where g(2 h k) and (2 k) denote reconstructon flters. An extenson of the decomposton scheme to 2d mages follows by the usual tensor product formulaton. The actual mproved mage fuson methodology can be developed: In the frst step a SIDWT decomposton s appled on each MS bands and PAN band wth specfc levels. Salent spatal nformaton s ncluded n detal components and spatal nformaton n approxmaton components. Snce larger absolute transform coeffcent correspond to sharper brghtness change, t s a good rule to select the coeffcents whose absolute values are hgher. Fugre. shows the schematc dagram of the basc structure of the proposed mage fuson scheme. Fuson operator F[ ] denotes that wavelet coeffcent maxmum selecton of MS bands and PAN band of the correspondng approxmaton scale. 4. EXPERIMENTAL RESULTS LANDSAT-7 ETM+ and SPOT mages are now avalable for the landslde nformaton nterpretaton n our study. Accordng to Jan(Lu,2), the 5-m resoluton LANDSAT-7 ETM+ PAN band s more sutable than -m resoluton SPOT PAN band for fuson wth color compostes of ETM+ MS bands. So we start wth ETM+ PAN and ETM+ MS bands fuson for testfyng the proposed applcable merger. ETM+ mage (27/39) taken on 3 July 2 was used for the study and 24*24 pxels ncludng dadpng landslde body,located n wan county, three gorge area, chna, s selected as test ste. The composton of band4(r)5(g)3(b) s chose as MS bands for landslde nformaton ndentfcaton (Fgure.2) accordng to Emerson(Emerson,23). (6)

3 Fgure 2. Locaton of the study area and test magery (color composte of bands4(red),5(green),3(blue)) Approxmate symmetry Daubeches3 wavelet functon wth support block of 5, flter length of 6 and moment vansh of 3 s chose because of ts strong detal descrpton ablty. Scale functon,wavelet functon and correspondng flters are shown n fgure 2. The MS bands and PAN band were decomposed nto three levels wth maxmum value selecton of approxmaton on level 3(Fgure 3.).Fgure 6. gve the selecton result of MS band3 and PAN band on approxmaton component. 4. Vsually Evaluaton for Landslde Informaton Enhancement Four fuson results all gve more dalpng landslde nformaton compared wth the orgnal MS bands composton mage(fgure 4.) vsually. The I-SIDWT fuson method gve the best vsual effect than other three fuson methods referrng to the hghlghted dadpng landslde body nformaton and There s a greater contrast between the body and the about area. PCA merger gve the worst result. IHS and BT method almost gve the same vsual effect..5 Scalng functon ph Decomposton low-pass flter Reconstructon low-pass flter Fgure 3. scale functon,wavelet functon and correspondng flters Wavelet functon ps Decomposton hgh-pass flter Reconstructon hgh-pass flter Dadpng Landslde Fgure 4. Vsual analyss of the color compostons for dadpng landslde(from left to rght are TM4-5-3, IHS, PCA, BT, Improved SIDWT) 4.2 Quantty Evaluaton of Dstnct Megers In order to gve a quantty evaluaton of the test magery, two ndexes are consdered here(hu,22): Shannon Entropy Entropy s a synthetc ndex for magery nformaton contents. Probng to a 8-bts mage, Shannon Entropy s defned as:

4 255 H ( x) = log 2 = p p (7) N N 2 [ ] F(, j) L(, j) j σ = (9) = = MN where, p s the probablty of graylevel n the evaluated regon approxmately gven by: where, M, N s the dmensons of the magery; F(,j) and L(,j) denote the gray value of the fused and the low spatal resoluton mage respectvely. p = f N (8) In Table., We show the values of quanttatve evaluaton ndexes of the merged mages for dfferent fuson methods descrbed and the orgnal ETM+ MS bands. f s the frequency of graylevel ; N denote the total pxels of the mage. The hgher the value of Shannon entropy, the more textural nformaton of the fused mages, whch ndcate the better merger. Standard devaton Standard devaton ndcators: a performance measure σ s defned as the standard devaton of the dfference mage between the fused mage and the low spatal resoluton MS bands: The lower the value of ths parameter, the better the spectral qualty of the merged mage. They should be as close to as possble. The hgh nformaton quantty of the merged mages obtaned usng I-SIDWT s obvous because of the hghest shannon entropy. At the same tme, I-SIDWT merger keep better spectral qualty than other three mergers except IHS merger at MS band5 ndcated by standard devaton. however, the false color composton of the merged mage(fgure 5.) wth IHS merger vsually compared wth I-SIDWT shows poor qualty. ETM+ I-SIDWT IHS BROVEY PCA TM Band3 Standard devaton Shannon Entropy TM Band4 Standard devaton Shannon Entropy TM Band5 Standard devaton Shannon Entropy Table. The values of quanttatve evaluaton ndcators of the merged mages for dfferent fuson methods and the orgnal ETM+ bands 5. CONCLUSION The mproved SIDWT fuson method presented n ths paper allow to obtan hgher qualty probng to the test magery than those obtaned applyng the IHS, BT and PCA merger. Ths can be explaned by the preservaton of more spatal nformaton of PAN band and spectral nformaton of MS bands. It s necessary to develop approprate merger n ad of landslde nformaton nterpretaton. Dfferent fuson methods show dfferent mprovement on landslde nformaton. The mproved SIDWT fuson method showed sgnfcant mprovement for the landslde body ndentfcaton than other methodologcal approaches. The presented method can also be appled to other magery from other sensors for dfferent applcaton objectve. 6. AKNOWLEDGEMENT Ths work was carred out under Chna s Natonal Socal Development Research Programme funded by the Mnstry of Scence and Technology (approved No. 23DIA6N5 and 24DIB7). REFERENCES Carper,W.J.,Lllesand,T.M.;Kefer,R.W.,99.The use of Intensty-Hue-Saturaton transformatons for mergng Spot Panchromatc and Multspectral Image data. Photogrammetrc Engneerng and Remote Sensng,56(4),pp Emerson,V.M., Lela,M.G.F.,Fernando,V., Antono,N.D.C.S.R., 23.Evaluaton of HIS,PCA and Wavelet Transform fuson technques for the ndentfcaton of landslde scars usng satellte data. Anas XI SBSR,Belo Horzonte,Brasl,5- abrl,inpe,pp Hu,Z.l.,Guo,D.Z., Zhang,H.R.,22.Data fuson between satellte SAR mage and TM mage based on wavelet textural nformaton.acta geodaetca et cartographca snca. 3(4): pp Lu,J.G.,2.Evaluaton of Landsat-7 ETM+ Panchromatc band for mage fuson wth multspectral bands.natural Resources Research,9(4),pp

5 Mara,G.A.,José,L.S., 24.Raquel,G.C.,and Rafael,G.,Fuson Vrabel, J.,996.Multspectral Imagery Band Sharpenng of Multspectral and panchromatc mages usng mproved HIS and PCA mergers based on Wavelet decomposton.ieee Study.Photogrammetrc Engneerng & Remote Sensng, 62(9),pp Transactons on geoscence and remote sensng,42(6),pp Welch, R. and W. Ahlers, 987. "Mergng Multresoluton SPOT HRV and Landsat TM Data." Photogrammetrc Unser,M.,995.Texture Classfcaton and Segmentaton usng Engneerng & Remote Sensng, 53 (3), pp Wavelet Frames. IEEE Trans, Image Processng,4(9), pp Yocky,D.A.,996.Multresoluton wavelet decomposton mage merger of Landsat Thermatc Mapper and Spot Panchromatc data. Photogrammetrc Engneerng and Remote Sensng,62(9),pp (a) The mproved SIDWT merger (b) The IHS merger (c) The BT merger (d) The PCA merger Fgure 5. Colour composte mages of merged TM bands4,5,3 and TM PAN band (a) (b) Fgure 5. (a) Approxmaton of SIDWT decomposton of MS band3 on level 3 (b)approxmaton wavelet coeffcent on level 3 after maxmum value selecton rule between MS band 3 and PAN band