TOWARDS AUTOMATED DEM GENERATION FROM HIGH RESOLUTION STEREO SATELLITE IMAGES

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1 TOWARDS AUTOMATED DEM GENERATION FROM HIGH RESOLUTION STEREO SATELLITE IMAGES Pablo d'angelo, Manfred Lehner, Thomas Krauss, Danelle Hoja and Peter Renartz German Aerospace Center (DLR), Remote Sensng Technology Instute, D Wesslng, Germany (Pablo.Angelo, Manfred.Lehner, Thomas.Krauss, Danelle.Hoja, Commsson IV, WG IV/9 KEY WORDS: spaceborne scanner systems, dgtal elevaon models (DEM), mage matchng, CARTOSAT-1, orthomage, accuracy analyss ABSTRACT: Hgh resoluon stereo satellte magery s well suted for the creaon of dgtal surface models (DSM). In ths paper, a system for hghly automated DSM and orthomage generaon based on CARTOSAT-1 magery s presented. The proposed system processes photometrcally corrected level-1 stereo scenes usng the raonal polynomal coeffcents (RPC) unversal sensor model. The RPC are derved from orbt and attude nformaon and have a much lower accuracy than the ground resoluon of approxmately 2.5 m. Ground control ponts are used to esmate affne RPC correcon. Accurate GCP are not always avalable, especally for remote areas and large scale reconstrucon. In ths paper, GCP are automacally derved from lower resoluon reference mages (Landsat ETM+ Geocover and SRTM DSM). It s worthwhle to note that SRTM has a much hgher lateral accuracy than the Landsat ETM+ mosac, whch lmts the accuracy of both DSM and orthorecfed mages. Thus, affne RPC correcon parameters are esmated by algnng a prelmnary DSM to the SRTM DSM, resulng n sgnfcantly mproved geolocaon of both DSM and orthomages. Robust stereo matchng and outler removal technques and pror nformaon such as cloud masks are used durng ths process. DSM wth a grd spacng of 10 m are generated for 9 CARTOSAT-1 scenes n Catalona. Checks aganst ndependent ground truth ndcate a lateral error of 3-4 meters and a heght accuracy of 4-5 meters. Independently processed scenes algn at subpxel level and are well suted for mosacng. 1. INTRODUCTION In May 2005 Inda launched ts IRS-P5 satellte wth CARTOSAT-1 nstrument whch s a dual-opcs 2-lne alongtrack stereoscopc pushbroom scanner wth a stereo angle of 31 and the very nteresng resoluon of 2.5 m. The operaonal use of the data s descrbed n (Srvastava et al, 2007). The CARTOSAT-1 hgh resoluon stereo satellte magery s well suted for the creaon of dgtal surface models (DSM). In ths paper, a system for hghly automated DSM generaon based on CARTOSAT-1 stereo scenes s presented. CARTOSAT-1 stereo scenes are provded wth raonal polynomal funcons (RPC) sensor model, derved from orbt and attude nformaon. The RPC have a much lower accuracy than the ground resoluon of approxmately 2.5 m. Tradonally, subpxel accurate ground control ponts (GCP) are used n prevous studes to esmate bas or affne RPC correcon parameters requred for hgh qualty geolocaon of HRSI mages. Such hghly accurate GCP are usually derved from a DGPS ground survey or hgh resoluon orthomages and dgtal elevaon models. For many applcaons, especally ones demandng near real-me results, such as desaster assessment tasks n remote regons, hghly accurate GCP data s often not avalable. Wthout accurate GCPs, CARTOSAT-1 scenes are of lmted use, snce bas or affne RPC correcon s requred before CARTOSAT-1 scenes can be used for DSM extracon and orthorecfcaon (Lehner et al, 2007). We propose the use of wdely avalable lower resoluon satellte data, such as the Landsat ETM+ and SRTM DSM datasets as a reference for RPC correcon. Dgtal surface models (DSM) are derved from dense stereo matchng and forward ntersecon and subsequent nterpolaon nto a regular grd. Snce stereo matchng s unrelable n large, homogeneous mage areas, such as felds, meadows and water bodes, as well as n complcated terran wth occlusons and shadows, strct consstency checks are used durng matchng. The frst secon of the paper descrbes the process used for DSM generaon. The second part evaluates the processor usng 9 CARTOSAT-1 stereo pars. 2. DSM GENERATION The DSM generaon process conssts of the followng man steps, mplemented as part of the DLR XDbas mage processng system. 1. Stereo matchng n eppolar geometry 2. Affne RPC correcon and algnment to reference DEM 3. Forward ntersecon and outler removal 4. Interpolaon 5. Orthorecfcaon 6. Qualty nspecon and manual edng A CARTOSAT-1 stereo scene conssts of a nadr lookng mage wth a along track lt of -5, a forward lookng mage wth a along track lt of 26. They are named Aft and Fore throughout ths paper.

2 2.1 Stereo Matchng Herarchcal ntensty based matchng s used for matchng the stereo pars and the reference mage. It conssts of two major steps, herarchcal matchng to derve hghly accurate e ponts, followed by a regon growng step to generate a dense set of e ponts. The nal matchng step uses a resoluon pyramd (Lehner&Gll, 1992; Kornus et al., 2000) to cope even wth large stereo mage dstorons stemmng from carrer movement and terran. Large local parallaxes can be handled wthout knowledge of exteror orentaon. The selecon of pattern wndows s based on the Foerstner nterest operator whch s appled to one of the stereo partners. For selecon of search areas n the other stereo partner(s) local affne transformaons are esmated based on already avalable e ponts n the neghborhood (normally from a coarser level of the mage pyramd). Te ponts wth an accuracy of one pxel are located va the maxmum of the normalzed correlaon coeffcents computed by sldng the pattern area all over the search area. These approxmate e pont coordnates are refned to subpxel accuracy by local least squares matchng (LSM). The number of ponts found and ther fnal (subpxel) accuracy acheved depend manly on mage smlarty and decrease wth ncreasng stereo angles or me gaps between magng. The procedure results n a rather sparse set of e ponts well suted for ntroducon nto bundle adjustment and as an excellent source of seed ponts for further densfcaon va regon growng. The second step uses the regon growng concept frst publshed by Otto and Chau n the mplementaon of TU Munch (Hepke et al., 1996). It combnes LSM wth a strategy for local propagaon of nal condons of LSM. Eppolar stereo mages are used n the regon growng step, and the propagaon strategy s modfed to enforce ponts located on the eppolar lnes. Stereo e ponts devang more than 0.5 pxels from the eppolar geometry are removed. A quas-eppolar stereo par wth eppoles correspondng to the mage columns s generated by algnng the columns of the Fore mage wth the Aft mage, usng hghly accurate matches from the pyramdal matchng step. Varous methods for blunder reducon are used for both steps of the matchng: Threshold for correlaon coeffcent 2-dreconal matchng and threshold on resulng shfts of the coordnates Threshold on the devaon from eppolar geometry. In areas of low contrast the propagaon of affne transformaon parameters for LSM n regon growng leads to hgh rates of blunders. In order to avod ntruson nto homogeneous mage areas (e.g. roof planes wthout structure) the extracted mage chps are subject to (low) thresholds on varance and roundness of the Foerstner nterest operator. Ths and the many occlusons found n densely bult-up areas maged wth a large stereo angle create lots of nsurmountable barrers for regon growng. Thus, for hgh resoluon stereo magery the massve number of seed ponts provded by the matchng n step one (mage pyramd) turns out to be essenal for the success of the regon growng. The numbers of e ponts found and ther subpxel accuracy s hghly dependent on the stereo angle. A large stereo angle (large base to heght rao b/h) leads to poorer numbers of e ponts and to lower accuracy n LSM va ncreasng dssmlarty of (correctly) extracted mage chps. 2.2 GCP collecon and affne RPC correcon Prevous studes (Lehner et al., 2007) have shown that the CARTOSAT-1 RPC ground accuracy s n the order of hundred meters. Addonally, forward ntersecon performance wthout RPC correcon s poor and results n large resduals n mage space. The esmaon of affne RPC correcon parameters requres well dstrbuted GCP wth subpxel accuracy. In many applcaon scenaros, such as connent wde reconstrucon or crss support applcaons, acqurng the requred GCP s very tedous or mght even be mpossble, f a fast response s requred. Gobal and easly avalable reference datasets are the OnEarth Landsat ETM+ Geocover mosac and the SRTM elevaon data. The accuracy of these datasets s low compared to the hgh resoluon CARTOSAT-1 mages. The Landsat ETM+ Geocover mosac s specfed wth a lateral error of 50m. The absolute lateral error of SRTM amounts to 7.2m m (LE90, dependng on the connent), wth an absolute heght error of 4.7m to 9.8m (Rodrguez et al., 2005). GCPs are collected by transfer of hghly accurate e ponts between the CARTOSAT-1 Aft and Fore mages to the Landsat reference mage and extracon of the correspondng heght from SRTM. The matchng procedure starts by algnng the CARTOSAT-1 Aft mage to the ETM+ reference by usng the corner values provded n the CARTOSAT-1 metadata. The frst step of the herarchcal matchng procedure descrbed n Secon 2.1 s appled to obtan e ponts between the ETM+ and CARTOSAT-1 Aft scenes. A smlar matchng could be done by matchng the Fore mage aganst the ETM+ mage, t would however yeld dfferent e ponts and thus GCPs for the Aft and Fore mage. Snce affne RPC correcon s performed separately for each mage, a good lnk between the Aft and Fore mages s requred to ensure good forward ntersecon behavour. Thus, hghly accurate stereo e ponts between the CARTOSAT-1 Aft and Fore mages are selected by applyng strct thresholds on the bdreconal matchng shft (0.1 pxels) and correlaon coeffcent (0.8). The Aft coordnates of these stereo e ponts are then used as nterest ponts and matched aganst the full resoluon ETM+ scene, usng the prevous Aft vs. ETM+ matchng as nal approxmaon. Ths yelds the geographc poson of the stereo e ponts. Fnally, 3D GCPs for both Aft and Fore scene are obtaned by blnear nterpolaon of the SRTM DSM. We use a non-nterpolated C band SRTM, where holes larger than 2 pxels are sll open. Ths avods dervng GCP from nterpolated heghts. Affne RPC correcon parameters are esmated both for the Aft and Fore scene RPC correcon by DSM algnment After the algnment based on ETM+ and SRTM reference data, forward ntersecon resduals are sgnfcantly mproved, but the lateral accuracy s sll lmted by the ETM+ Geocover reference. To take advantage of the hgher accuracy of the SRTM dataset a second RPC correcon step s necessary. A 3D pont cloud s calculated by forward ntersecon of a subset of the stereo e ponts. The pont cloud s algned to the SRTM DSM. It s assumed that the heght z of a pont P located at

3 (x,y,z ) equals the reference DSM heght h D (x,y ) at the correspondng poson (x,y ): h ( x, y ) = z (1) D A 3D affne transformaon s used to algn the nal stereo pont cloud to the SRTM DSM: where p r r p = A (2) r T p = ( x y z 1) s the orgnal pont, A s a 3x4 matrx, r p = x y z s the transformed pont. ( ) T The affne transformaon matrx A s esmated usng an terave least mean squares algorthm. Usng Eq. (1) and (2), the followng observaon equaon s obtaned. D v = h ( x, y ) z (3) Snce the model s non-lnear, the soluon s obtaned teravely. An denty transform s used as nal approxmaon, snce the stereo ponts are not far from the reference. It s lkely that the stereo pont cloud, and to a smaller extend the DSM contans outlers, whch cannot be handled by a standard least mean squares algorthm. After the nal esmaon, ponts wth a resdual larger than 3 mes the standard devaon are removed and a new transformaon s esmated. Ths procedure s repeated unl less than 0.3% outlers are detected and the squared sum of the outler resduals accounts for less than 5% of the squared sum of all resduals. The esmated affne transformaon could be used to algn the fnal DSM to the SRTM reference and thus mprove ts accuracy. Orthomages would however sll be lmted by the ETM+ accuracy. It s desrable to nclude the correcon n the RPC models, too. Ths s done by algnng the 3D stereo ponts to SRTM and usng them as GCP for a second RPC correcon whch yelds the fnal affne RPC correcon used n all subsequent steps. 2.3 Forward ntersecon and outler removal Forward ntersecon s done va terave least squares adjustment usng 4 observaon equaons and derves object space coordnates n Geographc coordnates n WGS84 datum. (Grodeck et al, 2004, Lehner et al, 2007). The resduals n mage space are used for a further blunder reducon step. Ponts wth a resdual larger than 0.5 pxels are rejected. Of course, only resduals n cross track drecon wll be effecve because wrong row coordnates of e ponts are translated nto wrong heght values f only two stereo partners are avalable (stereo magng drecon). The forward ntersected ponts sll contan a small amount of blunders due to matchng errors n regons wth sparse texture. To elmnate gross outlers, a reference check aganst the SRTM DSM s performed. All ponts whose heght devates more than 3 mes the heght error of the SRTM are rejected. The SRTM heght error map was found to be a good approxmaon of the true heght error (Rodrguez et al. 2005), and s used to dynamcally adjust the heght dfference threshold. Typcal thresholds are 24 m n flat areas, and 75 m n mountanous areas. 2.4 DSM nterpolaon Result of matchng and forward ntersecon s a set of 3D ponts represenng the Earth surface (ncludng f.e.. tree tops) acqured by the stereo mages. To ease further applcaons, the rregular pont cloud s transferred to a regularly spaced grd wth a spacng of 10 m. If mulple ponts fall nto the same grd cell, ther heghts are averaged to form a new pont. The ponts are connected by Delauney trangulaon nto a trangulated rregular network (TIN). Fnally, the trangles are supermposed on the regularly spaced grd of the resulng DSM. For each trangle the plane defned by the three verces s calculated. To each pxel nsde the trangle the heght value nterpolated on ths plane s assgned (Hoja et al., 2005). 2.5 Orthorecfcaon Orthomages wth user defned datum and projecon are created by orthorecfcaon of the Aft mage wth the generated DSM and the affne corrected RPC. 3. EVALUATION The DSM creaon process descrbed above s evaluated wth 9 CARTOSAT-1 scenes of Catalona. Scene Cat was part of the Cartosat scenfc assessment programme, whle the remanng 8 scenes have been provded by Euromap. The Landsat ETM+ Geocover mosac and the SRTM C band DSM have been used as sources for GCP collecon. Two reference DTM wth a GSD of 15 m and 10 orthomages wth a resoluon of 0.5 m have been provded by the Instut Cartographc de Catalunya (ICC) and are only used as ground truth durng the evaluaon. The locaon of the scenes and ground truth data s shown n Fgure 1. The scenes are mostly cloudless. Scene 117/207 contans two large clouds n the upper left corner, coverng most of the overlap between wth scene 116/207. The scenes located near the coastlne contan both flat areas along the coast as well as the Montseny mountan range wth peaks of over 1600 meters. As shown n Table 1, the scenes were aqured early n the year, leadng to large shadows n the mountanous areas. Abbrevaon for Imagng date the paper for aft and fore scenes Cat-A/F 01 Feb /207-A/F 16 Feb /208-A/F 16 Feb /207-A/F 05 March /208-A/F 05 March /209-A/F 05 March /207-A/F 25 Jan /208-A/F 25 Jan /209-A/F 25 Jan Table 1: CARTOSAT-1 scenes evaluated n ths paper 3.1 Matchng The herarchcal matchng procedure descrbed earler yelds a large number of good matchng ponts, see Table 5 for the amount of mass e ponts extracted from each scene.

4 1 5 E 2 E 2 5 E Reference DEM Reference DEM 1 Cat Northng (m) E 2 E 2 5 E Fgure 1: Geographc layout of evaluated CARTOSAT-1 scenes and ICC reference data used for verfcaon. 3.2 RPC correcon Matchng and thus GCP collecon between CARTOSAT-1 and ETM+ scenes s hndered by the large me and resoluon dfferences. Most scenes of the ETM+ mosac have been captured between 1999 and 2001, resulng n large dfferences between CARTOSAT-1 and ETM+ scenes. Due to the large dfferences n appearance, relavely loose thresholds on correlaon (0.7) and bdreconal matchng coordnate shft (0.5 pxels n the ETM+ mage) have been used durng GCP collecon. A suffcent number of well dstrbuted GCP s found for all 9 scenes. An terave outler removal procedure s appled durng the affne RPC correcon esmaon. Between 856 and 93 GCP are used for RPC correcon. The mage space resduals of the GCP are qute large, wth standard devaon between 1.7 and 2 pxels, mostly due to the large resoluon dfference between CARTOSAT-1 and ETM+. No systemac error s vsble n the resduals. The C-SAP demonstrated that subpxel resduals can be acheved when a few hgh qualty and well dstrbuted GCP are avalable (Lehner et al., 2007). From the above results, t s expected that the Landsat ETM+ mosac s not a sutable base for dervng GCP wth the accuracy requred for CARTSAT-1. The DSM based RPC refnement descrbed n secon s thus used to further reduce the error. To esmate the true accuracy of the two RPC correcon approaches, 68 checkponts have been measured n the ICC orthomages and the stereo partner Cat-A. The heght of each checkpont s derved from the ICC DTM. These measurements have been automacally transformed nto Cat-A/F e ponts va least squares matchng. 6 wndow szes from 17 to 27 have been used n LSM n order to get stascal values for the accuracy. Forward ntersecon of these stereo e ponts results n object space posons. The lateral and heght dfferences between stereo ponts and checkponts are gven n Table 2. It s obvous that the correcon based on GCP derved from ETM+ and SRTM leads to a hgh shft n locaon and heght. Consderng the 15 m resoluon of ETM+, a mean dfference of 12.5 m s sll a good result and ndcates subpxel accuracy of the ETM+ Geocover mosac n the studed area. After algnng the stereo ponts to SRTM and re-esmaon of the affne RPC correcon, the lateral dsplacement reduces to 3.5 m. Ths s a very good result, especally when consderng the 90 m grd spacng of the SRTM. Fgure 2 shows the lateral shfts of all checkponts m Easng (m) Fgure 2: Lateral error of Cat scene for the two affne RPC correcon methods, measured usng ndependent checkponts. Red, thck arrows: ETM+ and SRTM GCP. Blue, thn arrows: Algn to SRTM. The arrow lengths are scaled by a factor 200. RPC correcon Lateral dfference (m) Heght dfference (m) reference Mean σ Mean σ ETM+, SRTM Algn to SRTM Table 2: Accuracy of the two RPC correcon procedures, measured usng well dstrbured, ndependent checkponts. 3.3 Forward ntersecon and outler removal Forward ntersecon of the mass stereo e ponts performs well; no ponts are dscarded wth a relavely strct threshold of 0.5 pxels on the mage space resduals. A few gross blunders wth msmatches along the eppoles reman and are rejected due to ther devaon from the SRTM DSM. Table 3 shows the number of accepted ponts and ther mean heght dfference to the ICC reference DTM. When comparng the dfferences wth the checkpont evaluaon n secon 3.2, the larger heght errors and standard devaons are noceable. Ths s caused by the subopmal condons for mage matchng, such as the low sun angle and the mostly mountanous terran wth vegetaon. Especally n the Montseny mountan range located n the upper rght of the block, very large black shadows wth a dameter of several km can be found, leadng to large nterpolaon facets and resulng n a rather coarse DSM wth large facets. Most of scene 117/209 s covered by the ocean and the cty of Barcelona wth large buld up areas. When comparng the generated surface model wth the bare earth DTM provded by ICC, a negave heght dfference, as well as a larger standard devaon s expected n such areas. The negave mean heght dfference observed for all scenes s a good sgn and shows that the CARTOSAT DSM s located above the ICC DTM.

5 Scene Number accepted ponts (Mo.) Heght dfference to ICC DTM Mean (m) σ (m) Cat / / / / / / / / Table 3: Accepted object ponts stascs 3.4 DSM and Orthomage creaon After the outler removal step, a DSM on a 10 meter grd s nterpolated for all scenes. Fgure 4 shows the dfference between the ICC DTM and the generated DSM for the CAT scene. The consstency of the produced Aft/Fore orthomages s assessed by mage matchng. Hghly accurate e ponts between each ortho par have been establshed usng LSM. The mean shft vares between 0.28 and 0.30 pxels, the correspondng standard devaon between 0.15 and 0.18 pxels. Fgure 3 shows that the remanng subpxel shft between the Aft and Fore orthomages s slghtly regular. y (pxel) pxel x (pxel) Fgure 3: Shfts (averaged on a 150x150 pxel grd) between orthorecfed Aft and Fore mage of scene 116/ Mosacng After each scene has been processed ndependently, DSM and Aft orthomages of scenes ( )/( ) are combned nto orthomage and DSM mosacs. No further radometrc or geometrc adjustment has been appled. To assess the consstency of the resulng mosac, shfts between the neghbourng orthomages are computed by LSM matchng and shown n Table 4. Ths s a good result, consderng that no bundle block adjustment was used, and all scenes were processed ndependently. The Ortho and DSM mosacs are shown n Fgure 5. Fgure 4: Heght dfference (meter) obtaned by subtracng the CARTOSAT-1 DSM from the ICC DTM. Table 4: Path/Row Lateral shft (m) mean σ (115,116) / (116,117) / (115,116) / (115,116) / Lateral shft n overlappng areas of neghbourng orthomages. Except for the overlap between scene 115/209 and 116/209, subpxel shfts are found. 4. CONCLUSIONS A hghly automated DSM processor for CARTOSAT-1 scenes s presented. Key features nclude the automac collecon of reference data from Landsat ETM+ Geocover mosac and the SRTM DSM, a novel affne RPC correcon esmaon approach whch leads to ortho and DSM products wth much hgher lateral accuracy than the ETM+ Geocover mosac. Comparson wth reference data n Catalona ndcates a locaon accuracy of 3-4 meter, and a heght accuracy of 3-4 m n terran wth good pattern matchng characterscs. In mountanous terran and wth rather low sun elevaons the normal problems of too steep slopes and large shadow areas wthout enough matchng targets lead to coarse reconstrucon and local artefacts n the DSM. The ablty to produce qualty DSM and ortho products wthout manually measured, hghly accurate ground control ponts s especally valuable for emergency applcaons, mappng of remote areas and large scale DSM producon. Seamless mosacs can be formed, even f all scenes were processed ndependently. Further work ncludes development of comfortable manual qualty nspecon and edng tools, as well as mproved computaonal effcency and better handlng of occluded and shadowed areas n the stereo matchng module. ACKNOWLEDGEMENTS EUROMAP provded most of the CARTOSAT-1 scenes used for ths analyss, wth the excepon of the Cat scene, whch was provded by ISRO/SAC as part of the CARTOSAT-1 Scenfc Assessment Program. Acknowledgements also go to the Instut

6 DSM mosac Orthomage mosac Detal of CARTOSAT-1 DSM (c) Detal of orthomage mosac, showng the consstency of the ndependently processed scenes 115/208 and 116/208. Correspondng SRTM C Band DSM Fgure 5: Resulng orthomage and DSM mosacs. Cartographc de Catalunya for the delvery of adequate ground truth for Catalona. REFERENCES Grodeck, J., Dal, G., Lutes, J., 2004: Mathemacal Model for 3D feature extracon from mulple satellte mages descrbed by RPCs, ASPRS Annual Conf. Proc., Denver, Colorado, USA Hoja, D., Renartz, P., Lehner, M., 2005: DSM Generaon from Hgh Resoluon Satellte Imagery Usng Addonal Informaon Contaned n Exsng DSM, Proc. of the ISPRS Workshop 2005 Hgh Resoluon Imagng for Geospaal Informaon, Hanover, Germany Kornus W., Lehner M., Schroeder, M., 2000: Geometrc nflght calbraon by block adjustment usng MOMS-2P 3-lnemagery of three ntersecng stereo-strps, SFPT (Socété Francase de Photogrammétre et Télédétecon), Bullen Nr. 159, pp Lehner M., Gll, R.S., 1992: Sem-Automac Dervaon of Dgtal Elevaon Models from Stereoscopc 3-Lne Scanner Data, IAPRS, Vol. 29, part B4, Commsson IV, pp , Washngton, USA Lehner, M., Müller, Rupert, Renartz, P., Schroeder, M., 2007: Stereo evaluaon of CARTOSAT-1 data for French and Catalonan test stes, Proc. of the ISPRS Workshop 2007 Hgh Resoluon Earth Imagng for Geospaal Informaon, Hanover, Germany, May 29 June 1 Rodrguez, E., Morrs, C.S., Belz, J.E., Chapn, E.C., Marn, J.M., Daffer, W., Hensley, S., 2005: An assessment of the SRTM topographc products, Techncal Report JPL D-31639, Jet Propulson Laboratory, Pasadena, Calforna, 143 pp. Srvastava P.K., Srnvasan T.P., Gupta Amt, Sngh Sanjay, Nan J.S., Amtabh, Prakash S., Karkeyan B., Gopala Krshna B., 2007: Recent Advances n CARTOSAT-1 Data Processng, Proc. of the ISPRS Workshop 2007 Hgh Resoluon Earth Imagng for Geospaal Informaon, Hanover, Germany, May 29 June 1