InSAR MONITORING of LANDSLIDES using RADARSAT and ALOS
The value of InSAR time-series analysis to investigate natural and anthropogenic processes
Space-borne Interferometric Synthetic Aperture Radar (InSAR) has developed rapidly over the past 20 years and has proven to be a valuable tool for topographic mapping and surface deformation measurement. Because of its dense spatial coverage and competitive accuracy, InSAR has now become one of the most preferred geodetic methods for the study of a variety of natural and geological hazards like earthquakes, volcanoes, ground subsidence and landslides. Our capabilities for hazard monitoring have been further enhanced by advanced InSAR algorithms such as Persistent Scatterer (PS) and Small Baseline (SB) methods, that enable the retrieval of deformation time series and velocity maps from SAR data. In this study, we give an overview of the recent advances in SAR Interferometry for depicting time-dependent deformation, and present the results of several case studies where these methods are used to investigate the earthquake cycle and land settlement in Turkey, aquifer-system compaction in Iran and volcano deformation in South America.
Monitoring CO2 sequestration with a network inversion InSAR method
The capture, containment and long-term storage of CO2 is increasingly discussed as an important means to counter climate change resulting from the ongoing release of greenhouse gases into the atmosphere. This CO2 sequestration often requires the pumping of the gas into deep saline aquifers. However, before sequestration can be regarded as a longterm solution it is necessary to investigate under which conditions permanent and leakless capture of the CO2 is achieved in the substrate. We demonstrate that a combination of spaceborne synthetic aperture interferometry (InSAR) and ground based measurements of ground uplift caused by the underground release and spreading of the CO2 can be forged into a powerful tool to monitor sequsetration. We use a novel InSAR approach, which combines the benefits of a point-based persistent scatterer algorithm with a network inversion approach, and an additional temporal filter to remove atmospheric disturbances also at smaller scales down to 1 km and less. Using case studies from several injection wells we show that InSAR and ground based data in conjunction with geological and structural information above the aquifer, as well as detailed injection logs, allow to monitor the volumetric spread of CO2 at the mm per year level. For the majority of the studied wells CO2 appears to approach a stable sequestration state, however, in at least one case our results suggest leakage outside the aquifer.
Geodetic Volcano Monitoring Research in Canary Islands: Recent Results
The Canarian Archipelago is an oceanic island volcanic chain with a long-standing history of volcanic activity (> 40 Ma). It is located off the NW coast of the African continent, lying over a transitional crust of the Atlantic African passive margin. At least 12 eruptions have been occurred on the islands of Lanzarote, Tenerife and La Palma in the last 500 years. Volcanism manifest predominantly as basaltic strombolian monogenetic activity (whole archipelago) and central felsic volcanism (active only in Tenerife Island). We concentrate our studies in the two most active islands, Tenerife and La Palma. In these islands, we tested different methodologies of geodetic monitoring systems. We use a combination of ground- and space-based techniques. At Tenerife Island, a differential interferometric study was performed to detect areas of deformation. DInSAR detected two clear areas of deformation, using this results a survey-based GPS network was designed and optimized to control those deformations and the rest of the island. Finally, using SBAS DInSAR results weak spatial long- wavelength subsidence signals has been detected. At La Palma, the first DInSAR analysis have not shown any clear deformation, so a first time series analysis was performed detecting a clear subsidence signal at Teneguia volcano, as for Tenerife a GPS network was designed and optimized taking into account stable and deforming areas. After several years of activities, geodetic results served to study ground deformations caused by a wide variety of sources, such as changes in groundwater levels, volcanic activity, volcano-tectonics, gravitational loading, etc. These results proof that a combination of ground-based and space-based techniques is suitable tool for geodetic volcano monitoring in Canary Islands. Finally, we would like to strength that those results could have serious implications on the continuous geodetic monitoring system design and implementation for the Canary Islands which is under development nowadays.
ALOS PALSAR interferometry of the Taupo Volcanic Zone, New Zealand
Taupo Volcanic Zone, an area with dimensions of 50 (NW-SE) by 350 (SW-NE) km located in central North Island of New Zealand, currently experiences active continental spreading related to the subduction of the Pacific plate beneath the Australian plate. The area is characterized by intense tectonic activity and volcanic eruptions of different scales, for example, frequent small (0.1 km3) eruptions at Mt Ruapehu, the largest active stratotovolcano in New Zealand, and much larger (10 km3), but infrequent (1000-10,000 year recurrence interval), caldera eruptions. The potential for intense seismic and volcanic activity creates a significant hazard for the inhabitants of this region. At the same time pressure draw-down associated with withdrawal of geothermal fluids for power generation in TVZ causes notable ground subsidence at sites where subsurface formations are highly compressible (for example, parts of Tauhara, Wairakei, and Ohaaki geothermal fields). This can result in significant risk to infrastructure. In the past, multiple attempts were undertaken to use C-band differential interferometry for measuring ground deformation in this region but results were only partially successful because of a significant decorrelation effect caused by the dense vegetation. For this study we acquired over 50 ALOS PALSAR images in raw format across the TVZ region spanning December 2006 to February 2009 and interferometric processing was performed using GAMMA software. For this region PALSAR interferograms were coherent for time periods longer than one year and perpendicular baselines smaller than 2000 meters. Atmospheric and orbital errors were widely observed and corrected where possible. Stacking of interferograms was performed and results were analyzed. Signals of different magnitude and areal extents are observed around the region. For example, large regional uplift around Taupo township and large regional subsidence in the center of the Bay of Plenty are noted. Conversely, localized subsidence with rates close to 100 mm/year is observed at several geothermal sites; this is in reasonable agreement with ground based leveling measurements.
The use of GPS Radio Occultation technique for atmospheric corrections in InSAR data
Under favorable conditions, SAR Interferometry offers an ideal tool for monitoring the spatial extent and magnitude of ground surface deformation. Fluctuation in atmospheric conditions is a major source of error in repeat-pass interferometry, which can seriously compromise the accuracy of InSAR data. An accurate estimation of atmospheric parameters is therefore necessary for reliable InSAR measurements. The GPS Radio Occultation method is an innovative remote sensing technique for indirect measurement of atmospheric parameters using signals broadcast by GPS satellites. The GPS signals are influenced by the atmospheric refractivity field, resulting in a time delay and bending of the signal, which are analyzed to obtain temperature profile, pressure and water vapour in the atmosphere. In this study, we use GPS Radio Occultation data from the COSMIC mission, extract atmospheric parameters, and apply them to correct differential interferograms affected by atmospheric artifact.
Monitoring of Inter-tidal Flats using Multi-frequency Polarimetric SAR
Recently, there are several new fully polarimetric space-borne SAR systems in orbit, operating in most common Earth observation frequencies, X-, C-, and L- bands. These new satellites provide us for the first time in history fully polarimetric SAR data for routine Earth observation applications. There have been, however, very limited number of applications of fully polarimetric SAR in Earth and Environmental science developed so far. In the Earth system, there are several important transition zones, and one of them is the coastal zones. Well developed intertidal flats play important roles in the ecosystems, and coastal fisheries, as well as the environmental buffer zones. In this study, we have investigated several theoretical and semi-empirical models to simulate the scattering of polarimetric SAR signals over inter-tidal flats, and obtained inversion results of the observed SAR data. Actually field works were also carried out during the actual SAR data acquisition for ground truthing purposes and verification of the results. We will discuss the results and current status of inter-tidal flat research with fully polarimetric SAR data.