{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,28]],"date-time":"2025-10-28T15:03:15Z","timestamp":1761663795288,"version":"build-2065373602"},"reference-count":27,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2018,6,22]],"date-time":"2018-06-22T00:00:00Z","timestamp":1529625600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>Landslides can have complex, spatially strongly inhomogeneous surface displacement fields with discontinuities from multiple active lobes that are deforming while failing on nested slip surfaces at different depths. For synthetic aperture radar interferometry (InSAR), particularly at lower resolutions, these characteristics can cause significant aliasing of the wrapped phase. In combination with steep terrain and seasonal snow cover, causing layover and temporal decorrelation, respectively, traditional phase unwrapping can become unfeasible, even after topographic phase contributions have been removed with an external high-resolution digital surface model (DSM). We present a novel method: warp demodulation that reduces the complexity of the phase unwrapping problem for noisy and\/or aliased, low-resolution interferograms of discontinuous landslide displacement. The key input to our warp demodulation method is a single (or several) reference interferogram(s) from a high-resolution sensor mode such as TerraSAR-X Staring Spotlight with short temporal baseline and good coherence to allow localization of phase discontinuities and accurate unwrapping. The task of constructing suitable phase surfaces to approximate individual to-be-demodulated interferograms from the reference interferogram is made difficult by strong and spatially inhomogeneous temporal, seasonal, and interannual variations of the landslide with individual lobes accelerating or decelerating at different rates. This prevents using simple global scaling of the reference. Instead, our method uses an irregular grid of small patches straddling strong spatial gradients and phase discontinuities in the reference to find optimum local scaling factors that minimize the residual phase gradients across the discontinuities after demodulation. Next, for each to-be-demodulated interferogram, from these measurements we interpolate a spatially smooth global scaling function, which is then used to scale the (discontinuous) reference. Demodulation with the scaled reference leads to a residual phase that is also spatially smooth, allowing it to be unwrapped robustly after low-pass filtering. A key assumption of warp demodulation is that the locations of the phase discontinuities can be mapped in the reference and that they are stationary in time at the scale of the image resolution. We carry out extensive tests with simulated data to establish the accuracy, robustness, and limitations of the new method with respect to relevant parameters, such as decorrelation noise and aliasing along phase discontinuities. A realistic parameterization of the method is demonstrated for the example of the Fels Glacier Slide in Alaska using a recent late-summer high-resolution staring spotlight interferometric image pair from TerraSAR-X to demodulate. We show warp demodulation results for also recent but early-summer, partially incoherent interferograms of the same sensor, as well as for older and coarser aliased interferograms from RADARSAT-2, ALOS-1, and ERS.<\/jats:p>","DOI":"10.3390\/rs10070995","type":"journal-article","created":{"date-parts":[[2018,6,22]],"date-time":"2018-06-22T10:56:28Z","timestamp":1529664988000},"page":"995","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":12,"title":["A New InSAR Phase Demodulation Technique Developed for a Typical Example of a Complex, Multi-Lobed Landslide Displacement Field, Fels Glacier Slide, Alaska"],"prefix":"10.3390","volume":"10","author":[{"given":"Bernhard","family":"Rabus","sequence":"first","affiliation":[{"name":"School of Engineering Science, Simon Fraser University, Burnaby, BC V5A 1S6, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Manuele","family":"Pichierri","sequence":"additional","affiliation":[{"name":"School of Engineering Science, Simon Fraser University, Burnaby, BC V5A 1S6, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2018,6,22]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"333","DOI":"10.1109\/5.838084","article-title":"Synthetic aperture radar interferometry","volume":"88","author":"Rosen","year":"2000","journal-title":"Proc. IEEE"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"R1","DOI":"10.1088\/0266-5611\/14\/4\/001","article-title":"Synthetic aperture radar interferometry","volume":"14","author":"Bamler","year":"1998","journal-title":"Inverse Probl."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"193","DOI":"10.1007\/s10346-005-0003-2","article-title":"Survey and monitoring of landslide displacements by means of L-band satellite SAR interferometry","volume":"2","author":"Strozzi","year":"2005","journal-title":"Landslides"},{"key":"ref_4","first-page":"337","article-title":"Detection of landslide areas using satellite radar interferometry","volume":"66","author":"Kimura","year":"2000","journal-title":"Photogramm. Eng. Remote Sens."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"1629","DOI":"10.1029\/1999GL900262","article-title":"Monitoring very slow slope movements by means of SAR interferometry: A case study from a mass waste above a reservoir in the Otztal Alps, Austria","volume":"26","author":"Rott","year":"1999","journal-title":"Geophys. Res. Lett."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"2375","DOI":"10.1109\/TGRS.2002.803792","article-title":"A new algorithm for surface deformation monitoring based on small baseline differential SAR interferograms","volume":"40","author":"Berardino","year":"2002","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"31","DOI":"10.1016\/S0013-7952(02)00197-7","article-title":"Use of differential SAR interferometry in monitoring and modeling large slope instability at Maratea (Basilicata, Italy)","volume":"68","author":"Berardino","year":"2003","journal-title":"Eng. Geol."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"637","DOI":"10.1007\/s00024-007-0192-9","article-title":"An overview of the Small Baseline Subset Algorithm: A DInSAR technique for surface deformation analysis","volume":"164","author":"Lanari","year":"2007","journal-title":"Pure Appl. Geophys."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"399","DOI":"10.5589\/m09-028","article-title":"A simple robust two-scale phase component inversion scheme for persistent scatterer interferometry (dual-scale PSI)","volume":"35","author":"Rabus","year":"2009","journal-title":"Can. J. Remote Sens."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"8","DOI":"10.1109\/36.898661","article-title":"Permanent scatterers in SAR interferometry","volume":"39","author":"Ferretti","year":"2001","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"1685","DOI":"10.1109\/TGRS.2003.813278","article-title":"SAR monitoring of progressive and seasonal ground deformation using the permanent scatterers technique","volume":"41","author":"Colesanti","year":"2003","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"1952","DOI":"10.1126\/science.1098821","article-title":"Dynamics of slow-moving landslides from permanent scatterer analysis","volume":"304","author":"Hilley","year":"2004","journal-title":"Science"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"3460","DOI":"10.1109\/TGRS.2011.2124465","article-title":"A new algorithm for processing interferometric data-stacks: SqueeSAR","volume":"49","author":"Ferretti","year":"2011","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_14","unstructured":"Eppler, J., and Rabus, B. (2011, January 19\u201323). Monitoring urban infrastructure with an adaptive multilooking InSAR technique. Proceedings of the FRINGE 2011, Frascati, Italy."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"83611F","DOI":"10.1117\/12.918644","article-title":"Tunnel Monitoring with an Advanced InSAR Technique","volume":"8361","author":"Rabus","year":"2012","journal-title":"Proc. SPIE"},{"key":"ref_16","unstructured":"Costantini, M., Malvarosa, F., Minati, F., Pietranera, L., and Milillo, G. (2002, January 24\u201328). A three-dimensional phase unwrapping algorithm for processing of multitemporal SAR interferometric measurements. Proceedings of the IEEE International Geoscience and Remote Sensing Symposium, Toronto, ON, Canada."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"813","DOI":"10.1109\/36.673674","article-title":"A novel phase unwrapping method based on network programming","volume":"36","author":"Costantini","year":"1998","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"559","DOI":"10.1016\/S0094-5765(01)00020-0","article-title":"The Shuttle Radar Topography Mission (SRTM): A breakthrough in remote sensing of topography","volume":"48","year":"2001","journal-title":"Acta Astronaut."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"3317","DOI":"10.1109\/TGRS.2007.900693","article-title":"TanDEM-X: A satellite formation for high-resolution SAR interferometry","volume":"45","author":"Krieger","year":"2007","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"347","DOI":"10.1016\/j.jog.2005.07.013","article-title":"InSAR surface displacement field and fault modelling for the 2003 Bam earthquake (southeastern Iran)","volume":"40","author":"Stramondo","year":"2005","journal-title":"J. Geodyn."},{"key":"ref_21","doi-asserted-by":"crossref","unstructured":"Lu, Z., Dzurisin, D., Biggs, J., Wicks, C., and McNutt, S. (2010). Ground surface deformation patterns, magma supply, and magma storage at Okmok volcano, Alaska, from InSAR analysis: 1. Intereruption deformation, 1997\u20132008. J. Geophys. Res. Solid Earth, 115.","DOI":"10.1029\/2009JB006969"},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"166","DOI":"10.1016\/j.ijrmms.2012.05.008","article-title":"Integration of field characterisation, mine production and InSAR monitoring data to constrain and calibrate 3-D numerical modelling of block caving-induced subsidence","volume":"53","author":"Woo","year":"2012","journal-title":"Int. J. Rock Mech. Min. Sci."},{"key":"ref_23","unstructured":"Carrara, W.G., Goodman, R.S., and Majewski, R.M. (1995). Spotlight Synthetic Aperture Radar: Signal Processing Algorithms, Artech House."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"3695","DOI":"10.1109\/TGRS.2013.2274821","article-title":"The TerraSAR-X staring spotlight mode concept","volume":"52","author":"Mittermayer","year":"2014","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"246","DOI":"10.1109\/76.305870","article-title":"3-D motion estimation and wireframe adaptation including photometric effects for model-based coding of facial image sequences","volume":"4","author":"Bozdagi","year":"1994","journal-title":"IEEE Trans. Circuits Syst. Video Technol."},{"key":"ref_26","unstructured":"Lee, J.S., and Pottier, E. (2009). Polarimetric Radar Imaging: From Basics to Applications, CRC Press."},{"key":"ref_27","unstructured":"Newman, S.D. (2013). Deep-Seated Gravitational Slope Deformations near the Trans-Alaska Pipeline, East-Central Alaska Range. [Master\u2019s Thesis, Simon Fraser University]."}],"container-title":["Remote Sensing"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-4292\/10\/7\/995\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T15:09:45Z","timestamp":1760195385000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-4292\/10\/7\/995"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2018,6,22]]},"references-count":27,"journal-issue":{"issue":"7","published-online":{"date-parts":[[2018,7]]}},"alternative-id":["rs10070995"],"URL":"https:\/\/doi.org\/10.3390\/rs10070995","relation":{},"ISSN":["2072-4292"],"issn-type":[{"type":"electronic","value":"2072-4292"}],"subject":[],"published":{"date-parts":[[2018,6,22]]}}}