Research On The Monitoring Of Discontinuous Deformation By Differential SAR Interferometry

In recent decades, interferometric Synthetic Aperture Radar (InSAR) and differentialInSAR techniques are rapidly developed microwave techniques, which have been widelyapplied in earth science especially in surface deformation monitoring for their all- weatherconditions, day and night working, large coverage and high precision characteristics, such asthe monitoring of earthquake, volcano, mine collapse, land subsidence, landslide and glacieretc. which can greatly support the explanation, forecasting and mitigation of these geo-hazards.In fact, most of these geo-hazards mentioned above are discontinuous deformationin spatial domain, such as the fault of earthquake and volcano, ground fissures in urban areaand mine spot, the boundary of landslide and glacier etc. So it is essential to research thetheories and methods of the discontinuous deformation monitoring among the D-InSARapplications, which have great scientific and practical values for the fine explanation,mitigation and forecasting of such hazards.The main research of discontinuous deformation monitoring includes the positioningand monitoring of the discontinuous deformation, which are related to the qualitatively andquantitatively research of these geo-hazards respectively. According to the differentcharacteristics of discontinuous deformation, such as fissure length and shape, influencedwidth and deformation magnitude, this paper devides them into three parts as (1) Earthquakefault, with longer than 100 kilometers in length, up to several kilometers influenced widthand meter-scale deformation near fault; (2) Urban fissures, with maximum length about tenskilometers, the influenced width is between the magnitude of meters and 100 meters, and thedifference deformation across the ground fissure is about centimeters; (3) Mine collapsefissure, short fissures in length and always with regular shapes, and large subsidencemagnitude, some of them are larger than one meter. So this paper mainly focuses on thesethree kinds of deformation to analyze their positioning and monitoring theories and methodsas follows:Firstly, the principle, data processing flow, main errors, influenced magnitudes andmitigation measurements are analyzed. And the iteratively adaptive filtering algorithm ofinterferogram is deduced, which is verified with simulated and real SAR interferogramsrespectively.Secondly, the positioning methods of discontinuous deformation are mainly researched.The offset map based on the fine registration of master and slave SAR images is applied to detect the position of earthquake fault. The Manyi (Tibet) earthquake in 1997 is tested. Thepseudo-coherence map of filtered differential interferogram is applied to detect the groundfissure in urban and mine subsidence regions, where rationale and method are introduced.Xian ground fissure and Shaanbei mine subsidence are taken as examples. Still in order toincrease the positioning ability of small scale ground fissures and the absolute precision ofground fissure, some pre- installed Comer Reflectors (CR) are detected from Envisat ASARmagnitude images in Xian. And the method to evaluate the geocoding precision is pointedout with the fusion of CR and GPS techniques.Thirdly, three methods are pointed out for the discontinuous deformation monitoring as:(1) the deformation deduced from the offset maps can be used to monitor the deformationnear the earthquake fault, which can be well complementary to the conventional D-InSARresult at coherent region and provide a whole deformation map. Meanwhile Manyiearthquake is tested; (2) The full resolution interferogram is researched for mine collapsemonitoring. This method is preliminarily tested with Shaanbei mine subsidence; the result iscompared with traditional multi-looked InSAR result. (3) For the urban ground fissuresmonitoring, the L band SAR data as ALOS/PALSAR are applied to increase the monitoringability of InSAR deformation gradient, where the refined baseline estimation based onground control points (GCP) is mainly pointed out and the external DEM errors are alsodiscussed to increase the reliabilities of ALOS interferometry. Xian ground fissuredeformation in 2007-2008 is tested with ALOS/PALSAR and Envisat data.Fourthly, in order to mitigate the stochastic errors, such as atmospheric effect andprocessing errors, the stacking interferograms method is studied, and the linear subsidencerate and its RMS (root mean square) are calculated. Xian land subsidence during 2005 to2006 is tested using several interferograms, and the results are also calibrated with GPSresults during thesame period, and the InSAR precision is better than 1 cm/a.Lastly, ERS and Envisat data are applied to demonstrate the spatio-temporal landsubsidence and ground fissures evolution during 1992 to 2008.So, from the above research, the following conclusions can be drawn for thediscontinuous positioning and monitoring by applying the differential SAR interferometry:1,Phase noise is a key error for InSAR measurement, and the iteratively adaptivefiltering algorithm deduced in this thesis is a better algorithm than Goldstein and its modifiedform for its rational filter parameters determination. The simulated and real SARinterferograms verified this. 2,As for the positioning of discontinuous deformation, it should be taken differentmeasurements, exactly to say, the offset map based on fine corregistration can be applied forthe earthquake fault positioning and orientation for its large scale in length and greatdeformation gradient. Whereas the pseudo-coherence map of differential interferogram canbe well used to detect the urban ground fissures and mine subsidence edge. Meanwhile thepseudo-coherence maps in different acquisition times can also show evident spatio-temporalcharacteristics of land fissures. As for the positioning of small scale ground fissures, CRtechnique can be applied, which can also be used to evaluate the InSAR geocoding precisionby fusing with GPS.3,As for the discontinuous deformation monitoring three new or modified methods arepointed out. Firstly, the displacement from offset maps is applied complementary for themonitoring of the deformation near the earthquake fault, which can supply a wholedeformation map. Manyi earthquake (Mw =7.9) in 8 Nov. 1997 is tested. Secondly, the fullresolution interferogram can increase the deformation gradient monitoring ability, which canalso be divided into two different methods as single interferogram and multi-interferogramsbased on coherent points. The former on is verified with Shaanbei Bulianta mine monitoringtest, and more subsidence is achieved than traditional method. Thirdly, during the L bandALSO/PALSAR data interferometric processing, the baseline estimation error is greatlymitigated with refined baseline estimation method based on GCPs. And about 2cm/adeformation precision are achieved from the two-pass ALOS interferometric processing bycomparing with GPS results in the same time spanning.4,The stacking interferograms can effectively mitigate the stochastic errors, such asatmospheric effect and data processing errors, which can eventually increase the precision ofdeformation results. This method is applied for Xian ground fissure monitoring during 2005-2006, better than 1cm/a precision is achieved by comparing with GPS measurements andsome new fissures activities are firstly discovered.5,Lastly, differential interferometric method is applied to demonstrate spatio-temporalevolution of Xian ground fissures during 1992 to 2008, and some conclusions can be drawnas: the year of 1996 is the historically most active for ground fissure activities, in whichnearly 9 fissures as f3 to f11 in Xian have been detected as active fissures, while after 2000,the active fissures are mainly moved to f10 and f11, meanwhile three new fissures as f12,f13 and f14 came into being to south of Xian city, which are highly consistent with GPSresults and in-situ geological reconnaissance results.