SHADED-RELIEFS MATCHING AS AN EFFICIENT TECHNIQUE FOR 3D GEO- REFERENCING OF HISTORICAL DIGITAL ELEVATION MODELS

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1 Interntionl Archives of the Photogrmmetry, Remote Sensing nd Sptil Informtion Science, Volume XXXVIII, Prt 8, Kyoto Jpn 2010 SHADED-RELIEFS MATCHING AS AN EFFICIENT TECHNIQUE FOR 3D GEO- REFERENCING OF HISTORICAL DIGITAL ELEVATION MODELS F.J. Aguilr, *, I. Fernández, M.A. Aguilr, J.L. Pérez b, J. Delgdo b, J.G. Negreiros c Dept. of Agriculturl Engineering, Almerí University, L Cñd de Sn Urbno s/n, Almerí, Spin - (fguilr, ismelf, mguilr)@ul.es b Dept. of Crtogrphic Engineering, Geodesy nd Photogrmmetry, Jén University, Ls Lgunills s/n, Jén, Spin (jlperez, jdelgdo)@ujen.es c ISEGI University Nov de Lisbo, Cmpus de Cmpolide, Lisbon, Portugl - c8057@isegi.unl.pt Commission VIII, WG9 KEY WORDS: Mtching, DEM/DTM, Georeferencing, Cost, Shoreline, Monitoring ABSTRACT: Trditionl methods using eril photogrphs for shoreline mesurement often involved non-stereo photogrphy with no verticl informtion. However, digitl elevtion models (costl elevtion models or CEMs in our cse) re widely used in GIS to predict the impct of costl flooding nd Se Level Rise. Hence, we propose the CEM methodology to cope with computing shoreline position s the interfce between the lnd nd the wter t previously chosen verticl dtum. Furthermore, CEM evolution during the studied period my be used to quntify the costl lndscpe chnges. In ny cse n ccurte CEM is needed, both for newly-mde CEMs nd for historicl CEMs mostly compiled from historicl photogrmmetric flights. A new pproch to historicl CEM 3D geo-referencing is proposed long this work to void the costly nd time-consuming necessity of ground control points. The proposed methodology ws tested for geo-referencing historicl grid formt CEM, comprising little costl re of Almeri (South Spin), obtined by digitl stereo-photogrmmetry from B&W photogrmmetric flight tken in 1977 t n pproximted scle of 1: The reference CEM ws the 10 m grid-spcing digitl elevtion model produced by the Andlusi Regionl Government (Spin) coming from 1:20000 scle W&B photogrmmetric flight mde in The results obtined from this work my be deemed s very promising, showing high efficiency for historicl CEM 3D geo-referencing when it ws compred to trditionl methods such s photogrmmetric bsolute orienttion bsed on surveyed ground control points nd self-clibrting bundle djustment techniques. This preliminry pproch could be used s previous course mtching to be subsequently refined by 3D robust surfce mtching. 1. INTRODUCTION The costl re is one of the gretest environmentl nd economic ssets for ntion. Nowdys costl vulnerbility studies re experimenting growing demnd becuse the thretening tourism nd construction development joined to the future scenrio of widely predicted se-level rise (SLR) nd costl flooding due to climte chnge (Titus et l., 2009). In fct, digitl elevtion models (costl elevtion models or CEMs in our prticulr cse) re usully used to model SLR vulnerbility (Cowell & Zeng, 2003) nd costl flood risk (Webster et l., 2006). Nowdys CEM production is efficiently ccomplished by mens of LiDAR technology which is contributing, often coupled with pssive opticl imging, to wide rnge of costl scientific investigtions (Brock & Purkis, 2009). However, s LiDAR is reltively new technology, historicl dt beyond the pst decde re prcticlly unvilble (Jmes et l., 2006). Let us remember tht LiDAR mpping systems were not become vilble commercilly till the lte 90s. This is the reson becuse most of the studies heded up to obtin shoreline position nd evolution long certin period of time re minly bsed on rectified eril photogrphs, trditionl nd costly bech profiles from surveying techniques, topogrphic mps nd so on. Tht is to sy, trditionl methods using eril photogrphs for shoreline mesurement often involved non-stereo photogrphy with no verticl informtion. However, CEMs re widely used in GIS to predict the impct of costl flooding nd SLR. And more importnt, the ccurcy of those CEMs is clerly bound to the relibility of the derived results (Aguilr et l., 2010), s it is the cse for mps of potentil inundtion long costlines. Hence, we propose the CEM-bsed methodology to cope with the following complementry objectives: (i) to ccurtely compute shoreline position s the interfce between the lnd nd the wter t previously chosen verticl dtum. (ii) to use CEM evolution during the studied period to quntify the costl lndscpe chnges. In ny cse n ccurte CEM is necessry, both for newly-mde CEMs obtined from, for instnce, modern LiDAR technologies, nd for historic CEMs mostly compiled from historic stereo photogrmmetric flights. The ltter pproch requires number of ground control points (GCPs) to compute the bsolute orienttion of every stereo pir, surveying tsk tht usully becomes inefficient nd costly becuse the difficulty to ccurtely identify nd survey suitble set of ground points which could be pointed on the corresponding * Corresponding uthor. This is useful to know for communiction with the pproprite person in cses with more thn one uthor. 1002

2 Interntionl Archives of the Photogrmmetry, Remote Sensing nd Sptil Informtion Science, Volume XXXVIII, Prt 8, Kyoto Jpn 2010 historic photogrphs. Furthermore, in order to extrct high qulity topogrphic dt from historicl imgery, GCPs must lso be of high qulity nd must be well distributed in the photogrphs (Aguilr et l., 2010b). This is especilly importnt if cmer clibrtion informtion is incomplete or unvilble (Jmes et l., 2006). To void the necessity of ground control points, new pproch to historic CEM 3D geo-referencing is proposed long this work. 2. NEW APPROACH FUNDAMENTALS The bsic frmework regrding the new pproch fundmentls is shown in Fig. 1. Shortly, the proposed method strts from course reltive orienttion of the historic CEM, compiled by stereo-photogrmmetric techniques, where the stereo model y- prllx is removed by mens of n Automtic Reltive Orienttion (ARO). Previously, the historicl eril photogrphs hve to be scnned using photogrmmetric scnner. Subsequently, suitble photogrmmetric softwre must be utilised, in this cse ImgeSttion Digitl Mensurtion softwre (ISDM 4.0 from Z/I Imging), to crry out ARO process. As it is widely known, ARO is the process tht determines the reltionship between two overlpping imges, providing the position nd ttitude of one imge with respect to nother imge by utomticlly mtching tie points. Furthermore, it is highly recommendble to mnully mrk three control points (two full points XYZ nd one only Z point) to pply course seven prmeters Helmert 3D trnsformtion, obtining pre-oriented stereo-pir which will be very helpful to improve nd speed up the convergence of the subsequent shded-relief mtching process. Those control points only hve to present pproximted coordintes, both horizontl nd verticl, so they cn be esily extrcted from reference orthophotos (horizontl) nd supposing common Z (e.g. verge ground height long the working re). In this wy, Digitl Surfce Model (DSM) or, fter pplying filtering process, DTM (Digitl Terrin Model), both clled genericlly CEMs from here onwrds, cn be obtined by mens of stereo mtching techniques rnking over digitl imges (Aguilr et l., 2007). ImgeSttion Automtic Elevtions (ISAE 4.0 from Z/I Imging) ws the softwre used to generte DTM or DSM points from stereoimgery, providing lrge number of points by digitl mtching identicl fetures in ech of the stereo overviews. Next 2D shded-relief is generted for both the historic CEM (model to geo-reference) nd the reference CEM ( more recently obtined nd lredy geo-referenced CEM). In this regrds, different shded-reliefs my be tested, only chnging the solr elevtion nd zimuth, to optimize the finl 3D mtching between the historic nd reference CEM. In this sense, the lgorithm cn be repeted till obtining the best solution (Fig. 1). An utomtic mtching lgorithm bsed on the Scle Invrint Feture Trnsform (SIFT) hs been implemented to identify conjugted points in imge spce (pixel coordintes) belonging to reference nd historic CEM shded-relief imges. This lgorithm is ble to extrct fetures invrint to imge scle nd rottion. Furthermore these fetures re shown to provide robust mtching cross substntil rnge of ffine distortion, chnge in 3D viewpoint, ddition of noise, nd chnge in illumintion, so it cn be deemed s very suitble to our prcticl ppliction. The reder my find n in-depth description of SIFT method in Lowe (2004). This utomtic pproch turned out successful when the CEMs to mtch were reltively similr, but it did not when there ws gret level of disprity between CEMs due to importnt lndscpe modifictions (minly nthropogenic ltertions brought bout costl re development). In this cse mnul pproch would be needed llowing sub-pixel pointing on shded-relief imges (non presented dt). Finlly, the 3D coordintes for every pir of conjugte points were utomticlly extrcted from shded-relief (UTM ETRS89 Est nd North) nd CEMs (heights bove GRS80 ellipsoid). Those pirs of 3D points, previously trnsformed to geocentric coordintes, llowed computing n itertive lest squres registrtion between both CEMs by mens of robust seven prmeters 3D Helmert trnsformtion (Eqution 1, where the orthonorml rottion mtrix is represented by 3x3 elements which re trigonometric functions of the rottion ngles, nd ). The outliers found fter ech itertion were discrded nd not tken into ccount in the next one by estblishing threshold vlue to void gross errors due to lndscpe chnges (e.g. cut nd fill erthworks, new buildings, etc.). Tht threshold ws initilly set up to the pproximted uncertinty of the reference CEM, but sometimes hd to be incresed becuse t lest three points were needed to compute the 3D Trnsformtion. X Y = λ Z x ΔX y Y + Δ z ΔZ Afterwrds estimting the seven trnsformtion prmeters, 3D trnsformtion ws pplied to historicl CEM (using geocentric coordintes) to orientte it. All the processes constituting this bsis frmework, except for ARO nd CEM genertion, were progrmmed using MATLAB R2009. Figure 1. Flowchrt digrm showing the lgorithm frmework. (1) 1003

3 Interntionl Archives of the Photogrmmetry, Remote Sensing nd Sptil Informtion Science, Volume XXXVIII, Prt 8, Kyoto Jpn Study Site 3. STUDY SITE AND DATASETS The previously described shded-relief imge mtching method ws tested on one stereo-pir belonging to historicl photogrmmetric flight which will be lter described. The study re comprises hevily developed costl re of Almerí (Mediterrnen Se, South Spin). The working re ws concretely situted between the hrbour of Grruch nd Ants dry-rvine mouth (Fig. 2). This is currently high risk inundtion zone joined to n urbn re of high culturl density. control points to cope with this bundle djustment. In this cse we counted on 45 ground control points mesured by mens of DGPS technology. Furthermore, 44 independent check points (ICPs), not employed during the tringultion djustment, were used to check the process ccurcy. In this wy, the root men squre error (RMSE) ws clculted over the ICPs yielding the following results: RMSEx = 17.6 cm; RMSYy = 17.1 cm; RMSEz = 33.3 cm. Tht is very good result which ssures theoreticlly well-oriented DSM by using LPS stereo-mtching. In fct, this finl 1977 DSM my be considered s the best of ll possible ones, but it lso ws very time-consuming nd costly to obtin. Figure 2. Costl imge showing the study site. 3.2 Dtsets Dt corresponding to 1977: Come from n nlogic W&B stereo-pir belonging to the so-clled Agriculture photogrmmetric flight. This flight presented n pproximted scle of 1:18000 nd focl distnce round mm. It ws tken in A 10 m grid-spcing DSM ws crried out by mens of stereo mtching techniques (ISAE 4.0 from Z/I Imging) rnking over previously digitized imges (15 microns per pixel 30 cm ground smple distnce) with spectrl resolution of 8 bits. ISDM 4.0, from Z/I Imging, ws used to crry out the preliminry corse orienttion by mens of utomtic reltive orienttion (see section 2). Just for comprison purposes, clssicl photogrmmetric project ws crried out to obtin the best possible bsolute orienttion of the 1977 tested stereo-pir. For it, Leic Photogrmmetry Suite 9.1 (LPS) ws utilised. Becuse our historicl flight lcks of cmer clibrtion certificte, which is very usul by the wy, the corner coordintes for ech photogrph (fiducil mrks) were estblished using precise mnul mesurements mde on the positives. The principl point coordintes were fixed t zero, i.e. no offset existed between the principl point nd the fiducil centre. Focl length ws included becuse it usully ppers s mrginl dt in eril photogrphs. LPS llows pplying different Additionl Prmeters (APs) models in the eril tringultion process. The APs re the terms of polynomil expression incorported to the collinerity equtions which llow the modelling of systemtic errors coming from the bsence of cmer clibrtion certificte. This process is known s self-clibrtion djustment. In this cse the Brown s physicl model (14 prmeters) ws used, which compenstes for most of the liner nd nonliner forms of film nd lens distortions (Aguilr et l., 2010b). However, it is necessry high number nd ccurte ground Figure 3. Photogrmmetriclly-derived CEMs corresponding to 1977 (left) nd 2001 (right). Reference system UTM-ETRS Dt corresponding to 2001: The reference CEM corresponding to 2001 ws 10 m grid-spcing DTM produced by the Andlusi Regionl Government (Spin) throughout photogrmmetric flight tken in 2001 t n pproximted scle of 1: This originl DTM ws trnsformed from UTM Europen Dtum 1950 nd orthometric heights to the new Spnish officil geodetic system clled the Europen Terrestril Reference System (ETRS89) nd elipsoidic heights bove GRS80 ellipsoid. The corresponding DTM ccurcy ws estimted upon 62 DGPS check points locted t open terrin, yielding verticl RMSE vlue round 1.34 m. The historicl CEM to geo-reference (1977) nd the reference CEM (2001) re depicted in Figure 3 s 3D surfce mps. 4. RESULTS AND DISCUSSION 4.1 Automtic Shded-Relief Imge Mtching It is importnt to point out tht the mtching results my be very vrible depending on the solr position. In fct, utomted GCP loction in two imges consists of two steps. The first one extrcts sptil fetures from ech imge. Then, the fetures re pired by correspondence mtching. The success of the process depends, in prt, on the similrity of the fetures in the two imges, which is clerly relted to the solr position. This is the reson becuse the proposed methodology trets to itertively serch for n optiml solution chnging both solr zimuth nd solr elevtion. In Fig. 4 nd 5 re depicted the mtching results coming from different solr positions. In the cse of the 135º solr zimuth, only 26 conjugted points were successfully 1004

4 Interntionl Archives of the Photogrmmetry, Remote Sensing nd Sptil Informtion Science, Volume XXXVIII, Prt 8, Kyoto Jpn 2010 mtched out of 2139 nd 1368 key points found in 1977 nd 2001 shded-relief imges respectively. However, in the cse of 270º solr zimuth, only 23 conjugted points were finlly extrcted out of 2772 nd 1751 key points detected in 1977 nd 2001 shded-relief imges. It is importnt to highlight tht the most importnt is not only the number of pirs chieved but the homogeneous distribution of those points upon the working re. In the presented exmple, seems to be tht the shdedrelief corresponding to 135º solr zimuth obtined better distribution thn 270º solr zimuth did, bove ll when we notice tht the north re is only sustined by one pir of conjugted points in the second cse. re ws quite better in the second cse nd, furthermore, more mtched ground points were chieved. So we strongly recommend computing the 3D trnsformtion with not less thn 10 ground points, bove ll if the two mtching CEMs correspond to dynmic re where lndscpe chnge probbility my be considered s very high. Prmeter Solr zimuth 270º Solr elevtion 45º Estimted prmeters Solr zimuth 135º Solr elevtion 45º Vlue Accurcy Vlue Accurcy X m 0.74 m m 0.99 m Y m 0.77 m m 1.01 m Z m 0.74 m m 1.00 m º 0,00377º º 0,00418º º 0,00172º º 0,00372º º 0,00489º º 0,00503º , ,00253 Tble 1. Estimted vlues nd ccurcies for the computed seven prmeters 3D Helmert djustment (Geocentric coordintes with regrd to GRS80 reference ellipsoid). Figure 4. Results regrding utomtic shded-relief mtching (imge spce) for 135º solr zimuth nd 45º solr elevtion. Mtched GCPs X (m) Y (m) Z (m) Tble 2. Residuls in X, Y nd Z fter pplying the 3D Helmert djustment t the six utilized (out of 23) GCPs obtined by shded-relief imge mtching (zimuth 270º, elevtion 45º). Figure 5. Results regrding utomtic shded-relief mtching (imge spce) for 270º solr zimuth nd 45º solr elevtion D Helmert Adjustment Tble 1 shows the estimted trnsformtion prmeters for the computed 3D conforml trnsformtion. It is importnt to highlight tht, t glnce, the results regrding the two presented solr zimuths seem to be very similr. Even the ccurcies obtined from the lest squres vrince-covrince mtrix turned out to be slightly better in the cse of 270º solr zimuth. But it only ws mthemticl mirge, s we will check long the next section. In fct, though the residuls clculted t mtched ground points were lower for the cse of 270º zimuth thn those coming from the cse of 135º (Tbles 2 nd 3 respectively), the distribution round the whole working Mtched GCPs X (m) Y (m) Z (m) Tble 3. Residuls in X, Y nd Z fter pplying the 3D Helmert djustment t the ten utilized (out of 26) GCPs obtined by shded-relief imge mtching (zimuth 135º, elevtion 45º). 4.3 Surfce Mtching Results between 1977 nd 2001 The wrong orienttion of the preoriented CEM (courseoriented using ARO) cn be observed in Figure 6. An ccentuted rottion long NW-SE xis is clerly visible, 1005

5 Interntionl Archives of the Photogrmmetry, Remote Sensing nd Sptil Informtion Science, Volume XXXVIII, Prt 8, Kyoto Jpn 2010 leding to disperse residuls histogrm with n excessively high systemtic verticl error (see Tble 4). geomorphologicl fetures tht remin reltively stble long time. Afterwrds using the shded-relief imge lgorithm, the initil CEM position hs been notbly corrected nd the mtching results hve been clerly improved (Fig. 7). Becuse the lgorithm checks different solr position previously selected by the user, it is possible to obtin different solutions nd lter checking which the best is. In this sense, the 135º solr zimuth would be preferred despite the slightly poorer results estimted during the djustment process (Tble 1). Indeed some signed sttisticl results re shown in Tble 4. Notice tht the stndrd devition of the 135º solr zimuth cse is quite ner the RMSE estimted for the reference DTM (1.34 m). So the finl mtching my be considered s resonbly cceptble DSM - comprison Pre-oriented 1977 DSM 1977 DSM (240º-45º) 1977 DSM (135º-45º) Men (m) Signed residuls sttistics Mximum Minimum Stndrd (m) (m) devition (m) Tble 4. Signed residuls sttistics for the overlp re corresponding to the comprison between 1977 shded-relief oriented DSMs nd 2001 reference DTM. Figure 6. Mp of signed verticl residuls (pre-oriented DSM 1977 DTM 2001 within the overlp re) nd corresponding histogrm fter pplying the computed 3D Helmert prmeters. Figure 8. Mp of signed verticl residuls (oriented DSM 1977 DTM 2001 overlp re) nd corresponding histogrm fter pplying the computed 3D Helmert prmeters. Cse: 135º solr zimuth nd 45º solr elevtion shded-relief. Figure 7. Mp of signed verticl residuls (oriented DSM 1977 DTM 2001 within the overlp re) nd corresponding histogrm fter pplying the computed 3D Helmert prmeters. Cse: 270º solr zimuth nd 45º solr elevtion shded-relief. Then, nd judging numericl dt nd qulittive mps depicted in Tble 4 nd Figure 8, shded-relief imge mtching could be use to corsely co-register multi-temporl CEMs utomticlly without ground control points. It is needed to tke into ccount tht some of the gross errors detected in Figure 9 (green to red res) my be ctully no errors but lndscpe chnges due to erthworks (cut nd fills) projects. In this wy the proposed methodology seems to be very robust becuse loclized shdedrelief fetures used to compute the djustment re usully Figure 9. Mp of bsolute verticl residuls (oriented DSM 1977 DTM 2001 overlp re). Cse: 135º solr zimuth nd 45º solr elevtion shded-relief. The most importnt problem when registering multi-temporl DEMs is the intensity of temporl deformtion or chnge occurred between the period of the study. In most surfce mtching lgorithms the deformtion re is restricted to not 1006

6 Interntionl Archives of the Photogrmmetry, Remote Sensing nd Sptil Informtion Science, Volume XXXVIII, Prt 8, Kyoto Jpn 2010 much more thn 50% by introducing the so-clled differentil model nd improving the clssic lest Z-difference or LZD lgorithm, but it is rther complex nd needs previous rough co-registrtion or knowing bout the pproximted trnsformtion to crry out (Zhng nd Cen, 2008). Our pproch could be used s first step heded up to lter pply LZD-bsed surfce mtching lgorithm to refine the initil mtching s much s possible. This second step should include weight functions bsed on M-estimtors to mke the computtion more robust nd resisting to the presence of outliers (Miller et l., 2008). 4.4 Comprison between the 1977 Photogrmmetriclly Oriented DSM nd the Shded-relief Mtching Oriented DSM As it ws described in section 3.2.1, we previously mde up the best possible photogrmmetric bsolute orienttion for 1977 CEM by using lot of GCPs nd the self-clibrtion potentil of LPS system to overcome the problem due to the bsence of the cmer clibrtion prmeters. In Tble 5 cn be observed some residuls sttistics from which it is possible to stte tht the performnce of shded-relief mtching method my be considered s quite suitble. The fct is tht the stndrd devition is resonbly low, tking into ccount the flight scle nd the corresponding CEM uncertinty (round 1.10 m). It is necessry to dd tht different stereo-mtching methods to produce the 1977 CEM were utilised (tht is ISAE Z/I nd LPS systems). Hence there is n error from the get-go between both utomticlly generted CEMs tht ws estimted bout 0.74 m (stndrd devition) by mens of GCP-bsed surfce mtching pproch. DSM/DTM comprison DSM (135º/45º) PhotoDSM (1977) DSM (240º/45º) PhotoDSM (1977) 1977 PhotoDSM Mximum Minimum Stndrd (m) (m) devition (m) Tble 5. Residuls sttistics for the overlp re corresponding to the comprison between 1977 shded-relief oriented DSMs nd photogrmmetriclly oriented DSM (Photo DSM). It hs been lso dded the comprison for. 5. CONCLUSIONS The results obtined from this work my be deemed s very promising, showing good co-registrtion between reference nd historicl CEMs in hevily developed costl res. The point is the high efficiency nd robustness demonstrted for historicl CEM 3D geo-referencing when it ws compred to costly nd time-consuming trditionl methods such s photogrmmetric bsolute orienttion bsed on surveyed ground control points nd self-clibrting bundle djustment techniques. This preliminry pproch could be used s previous course mtching to be subsequently refined by 3D robust surfce mtching. 6. ACKNOWLEDGEMENTS The uthors re very grteful to Andlusi Regionl Government, Spin, for finncing this work through the Excellence Reserch Project RNM-3575 Multisource geosptil dt integrtion nd mining for the monitoring nd modelling of costl res evolution nd vulnerbility. Appliction to pilot re locted t Levnte de Almerí, Spin. 7. REFERENCES Aguilr, F.J., Crvjl, F., Aguilr, M.A., Agüer, F., Developing digitl crtogrphy in rurl plnning pplictions. Computers nd Electronics in Agriculture, 55, pp Aguilr, F.J., Mills, J.P., Delgdo, J., Aguilr, M.A., Negreiros, J.G., Pérez, J.L., Modelling verticl error in LiDARderived digitl elevtion models. ISPRS Journl of Photogrmmetry nd Remote Sensing, 65(1), pp Aguilr, M.A., Aguilr, F.J., Negreiros, J.G., 2010b. Selfclibrtion methods for using historicl eril photogrphs with photogrmmetric purposes. Anles de Ingenierí Gráfic, 21, pp Andlusin Government, Modelo digitl del Terreno de Andlucí. Relieve y orogrfí. Junt de Andlucí, Sevill, Spin (on DVD). Brock, J.C., Purkis, S.J., The emerging role of Lidr remote sensing in costl reserch nd resource mngement. Journl of Costl Reserch, 53, pp Cowell, P.J., Zeng, T.Q., Integrting uncertinty theories with GIS for modelling costl hzrds of climte chnge. Mrine Geodesy, 26, pp Jmes, T.D., Murry, T., Brrnd, N.E., Brr, S.L., Extrcting photogrmmetric ground control from LiDAR DEMs for chnge detection. The Photogrmmetric Record, 21(116), pp Lowe, D.G., Distinctive imge fetures from scleinvrint keypoints. Interntionl Journl of Computer Vision, 60(2), pp Miller, P., Mills, J.P., Edwrds, S., Bryn, P., Mrsh, S., Mitchell, H., Hobbs, P., A robust surfce mtching technique for costl geohzrd ssessment nd mngement. ISPRS Journl of Photogrmmetry nd Remote Sensing, 63(5), pp Titus, J.G., Anderson, K.E., Choon, D.R., Gesch, D.B., Gill, S.K., Gutierrez, B.T., Thieler, E.R., Willims, S.J., Costl sensitivity to se-level rise; focus on the mid-atlntic region. U.S. Environmentl Protection Agency, Ntionl Ocenic nd Atmospheric Administrtion, U.S. Geologicl Survey. U.S. Climte Chnge Science Progrm synthesis nd ssessment product 4.1, 320 pp. Webster, T.L., Forbes, D.L., Mckinnion, E., Roberts, D., Flood-risk mpping for storm-surge events nd se-level rise using LiDAR for southest New Brunswick. Cndin Journl of Remote Sensing, 32(2), pp Zhng, T., Cen, M., Robust DEM co-registrtion method for terrin chnges ssessment using lest trimmed squres estimtor. Advnces in Spce Reserch, 41, pp