G51C-0613
NASA's DESDynI InSAR and Multibeam LIDAR Mission
InSAR has been used to study surface deformation of the solid Earth and cryosphere and more recently in combination with LIDAR to study vegetation for estimates of biomass. The NRC decadal survey recommends that DESDynI (Deformation, Ecosystem Structure, and Dynamics of Ice), an integrated L-band InSAR and multibeam LIDAR mission, launch in the 2010-2013 timeframe. The mission will measure surface deformation for solid Earth and cryosphere objectives and vegetation structure for understanding the carbon cycle. The objectives of DESDynI are to 1) determine the likelihood of earthquakes, volcanic eruptions, and landslides, 2) Predict the response of ice sheets to climate change and impact on sea level, 3) characterize the effects of changing climate and land use on species habitats and carbon budget, and 4) monitor migration of fluids associated with hydrocarbon production and groundwater resources. This requires that surface deformation be measured globally at the level of 1-2 mm/yr to study geophysical processes and ice sheet mass balance. The mission also needs to develop globally consistent and spatially resolved estimates of aboveground biomass and carbon stocks to 10 Mg/ha or to within 20% and changes and trends to 2-4 Mg/ha. http://desdyni.org
G51C-0614
Using Lidar to distinguish leaf area index in cottonwood trees and improve riparian water use estimates in the Upper San Pedro River Basin
Estimation of riparian forest structural attributes, such as the Leaf Area Index (LAI), is an important step in identifying the amount of water use in riparian forest areas. In this research, small footprint lidar data were used to estimate biophysical properties of young, mature, and old cottonwood trees in the Upper San Pedro River Basin, Arizona, USA. Canopy height and maximum and mean laser heights were derived for the cottonwood trees from lidar data. Linear regression models were used to develop equations relating lidar height metrics with corresponding field measured LAI for each age class of cottonwoods. Four metrics (tree height, height of median energy, ground return ratio, and canopy return ratio) were derived by synthetically constructing a large footprint lidar waveform from small-footprint lidar data which were compared to ground-based high- resolution Intelligent Laser Ranging and Imaging System (ILRIS) scanner images. These four metrics were incorporated into a stepwise regression procedure to predict field-derived LAI for different age classes of cottonwoods. The Penman-Monteith model was then used to estimate transpiration of the cottonwoods using the lidar-derived canopy metrics. These transpiration estimates compared very well to ground-based sap flux transpiration estimates indicating lidar-derived LAI can be used to improve riparian cottonwood water-use estimates. Future research will attempt to fuse high spatial resolution multispectral or hyperspectral data and lidar data to improve classification results for species identification in the Upper San Pedro River Basin.
G51C-0615
Accuracy and Precision of Terrestrial LiDAR for Ground Deformation Monitoring
With controlled experiments and multiple occupations of a field site at Waimea Bay, Oahu, we are assessing the accuracy and precision for geodetic applications of the Optech ILRIS 3-D, a near-infrared (1.2 micron wavelength) Terrestrial-LiDAR (T-LiDAR) system. For the controlled experiments, we have built a stable table with a grid of peg holes and estimated static offsets and translations of a geodetic target (a Leica GPS antenna and radome). We scan the radome from variable distances (50 -1000 m) and with variable spot spacing. We use the 3D point cloud data to model the phase center of the radome by fitting all data points to a spherical model in a local co-ordinate frame. Preliminary results show that from over 1400 individual scans with spot-spacing ranging from 2 mm to 20 mm and over distances of 100-180 meters, the phase center of the radome derived from T-LiDAR measurements and solid modeling is achieved with better than 2-4 mm standard deviation. At the field site we have conducted more than 30 scans over a period of 3 months of an area with dimensions ranging from ~300 – 1000 m. While the beach face changes significantly during this time period, the area behind the beach does not allowing us to analyze the multiple natural and human-made targets there for their stability at a variety of distances and weather conditions.
G51C-0616
Airborne Laser Swath Mapping of the Denton Hills, Transantarctic Mountains, Antarctica: Mapping relations between glacial and tectonic landforms
New high-resolution digital elevation data were obtained by airborne laser scanning (ALS) using NASA's ATM system for the Denton Hills, along the coastal foothills of the Royal Society Range, Transantarctic Mountains. Digital elevation models, displayed as shaded-relief images and slope maps, portray geomorphic landscape features in unprecedented detail across the region. Lineaments etched into bedrock occur in both northwest and northeast orientations, and most likely represent fault arrays and associated fracture planes. Though the ages of these brittle structures are poorly constrained, at least some are neotectonic faults as shown by a northeast- trending lineament cutting a hanging valley terminal moraine. Mappable glacial features include the western limit of the Ross Sea drift, recording the limit of grounded ice at the Last Glacial Maximum; ridges and mounds interpreted as lake-ice conveyor deposits from proglacial lakes; and uplifted lake shorelines providing markers for documentation of postglacial rebound magnitude and rates. In addition to the ability to map the extent of glacial features spatially, the high-resolution topographic data makes it possible to quantify feature height, length and breadth, and to systematically measure such aspects as paleoshoreline elevations across the region.
G51C-0617
Alaska Glacier Observations with L-band InSAR and Lidar
In anticipation of the NASA DESDynI mission we investigate the use of L-band InSAR and spaceborne lidar to measure glacier velocities and surface elevation change on Alaska glaciers. PALSAR InSAR pairs from JAXA's ALOS satellite are used to produce coherence maps, fringe images, and radar line- of-sight displacement measurements. Speckle tracking is used to produce two-dimensional velocity maps. ICESat data are used to test the ability of spaceborne lidar to measure elevation change due to snow accumulation between October/November and March in high accumulation areas. Our initial study region is the upper Seward Glacier in southern Alaska. ICESat derived elevation change is available from four exact repeat tracks across the Upper Seward. Our previous ERS InSAR results for this area indicate a complex velocity field with speeds ranging from 10 to 100 m/year. Preliminary results from a PALSAR pair show areas of high coherence and wide spread success with speckle tracking.
G51C-0618
PIXEL: Japanese InSAR community for crustal deformation research
In anticipation of the launch of ALOS (Advanced Land Observation Satellite) by JAXA (Japan Aerospace eXploration Agency), and in order to expand and bolster the InSAR community for crustal deformation research in Japan, a couple of scientists established a consortium, PIXEL, in November 2005 in a completely bottom-up fashion. PIXEL stands for Palsar Interferometry Consortium to Study our Evolving Land. Formally, it is a research contract between JAXA and Earthquake Research Institute (ERI), University of Tokyo. As ERI is a shared institute of the Japanese universities and research institutes, every scientist at all Japanese universities and institutes can participate in this consortium. The activity of PIXEL includes information exchange by mailing list, tutorial workshop for InSAR software, research workshop, and PALSAR data sharing. After the launch of ALOS, we have already witnessed several earthquakes and volcanic activities using PALSAR interferometry. We will briefly show and digest some of those observation results.
G51C-0619
Crustal Deformation Caused by Earthquake Detected by InSAR Technique Using ALOS/PALSAR Data
The Japan Aerospace Exploration Agency (JAXA) launched the Advanced Land Observing Satellite (ALOS), which is commonly called eDaichif in Japanese, on 24th January 2006. This satellite has the Phased Array type L- band Synthetic Aperture Radar (PALSAR) following the mission of the Japanese Earth Resource Satellite-1 (JERS-1). The PALSAR is an advanced SAR sensor with up to 10 m of spatial resolution and variable off-nadir angle. The ALOS/PALSAR can determine the position and attitude with high accuracy by use of mounted dual frequency GPS system and high precision star trackers, and L-band SAR sensor is suitable to observe even heavily-vegetated area. Therefore it is expected much better coherent SAR images than the JERS-1 and the other previous C-band SAR satellites, and major step forward for InSAR (Interferometric SAR) technique. Actually, several outstanding results from InSAR measurements have been reported for the period after the launch. In 2007, two big earthquakes causing some damages on the periphery occurred in Japan. One is M6.7 Noto Peninsula earthquake on 25th March 2007, and the other is M6.8 off the Chuetsu region earthquake on 16th July 2007. Because both seismic faults inferred from these earthquakes are located at shallow depth beneath the bottom of the sea near the coast, obvious crustal deformation in a land area were detected by PALSAR data. In Japan, there is a dense nation-wide GPS network (GEONET) composed of more than 1200 GPS sites established and operated by Geographical Survey Institute and a lot of seismometers. Similarly GPS and seismometer could detect signals caused by the earthquakes, so these are noticeable cases from the standpoint of a comparison among various kinds of data. A remote sensing technique like the ALOS/PALSAR has advantage to observe and monitor a disaster occurred in a remote location where it is difficult to get and there has been little geophysical observation. In this presentation, we notice the case of earthquakes on 15th November 2006 in Kuril Islands and on 1st April 2007 in Solomon Islands as examples. The former earthquake (M8.3) in Kuril Islands was accompanied by tsunami and several meter of faulting. Simushir Island is situated about 200 km west of the epicenter, and has been observed by the PALSAR before and after the earthquake. Using differential InSAR technique, several fringes are detected and we presume that they show a co-seismic deformation. The latter earthquake (M8.1) in Solomon Islands was accompanied by large tsunami and caused a considerable damage in the area. The PALSAR has been observed these islands before and after the earthquake and detected an extensive co-seismic deformation areally using same technique as above. Then we try to compare these deformation to those induced from a fault model, and they show a good agreement. Compared with the amplitude image before the earthquake, several appearances of land area like uplift are recognized in the amplitude image after the earthquake. We went to the Solomon Islands in the end of July and confirmed the uplift. Additionally, we introduce a recent result of PALSAR data which targets at the M8.1 earthquake occurred in near the coast of central Peru on 15th August 2007. In the interferogram, extensive information of crustal deformation is detected.
G51C-0620
Interseismic secular deformation in Southern California from InSAR-derived maps over the time period between 1992 and 2006
We analyzed secular deformation in Southern California using an extensive catalog of InSAR data that spans 15 years between 1992 and 2006. We generated a map of the satellite line-of-sight displacements based on a stack of ~300 interferograms from 6 adjacent tracks of the ERS-1 and ERS-2 satellites covering Southern California. The main limitation to the accuracy of InSAR measurements of tectonic deformation is the atmospheric phase delay. We introduce a new method aimed to improve the signal-to-noise ratio in the InSAR- derived maps of secular deformation. The method involves identifying SAR acquisitions that are highly affected by atmospheric noise, and an optimal choice of interferometric pairs for stacking. We begin by generating a set of all possible interferometric pairs having baselines and time spans within prescribed limits. We then select interferograms with sufficiently high correlation. Subsequently, we identify noisy SAR acquisitions by means of calculating RMS of the phase signal. Finally, we generate a stack of interferograms by following a "connectivity tree" that minimizes contributions of noisy scenes. Using this method we obtained a continuous velocity field characterizing surface deformation in Southern California over the last 15 years. We identify interseismic deformation on a number of major faults, including those of the southern San Andreas system, and the Eastern California Shear Zone (ECSZ). We study the time dependency from 1992 to 2006 of those deformation patterns. Variations in the line-of- sight velocity across the Eastern California Shear Zone are non-monotonic, with the maximum along the strike of the Hector Mine fault of ~4 mm/yr, and total LOS velocity between the eastern and western boundaries of the shear zone of less than 2 mm/yr. We observe increases in the radar range to the east of ECSZ. This signal most likely results from subsidence east of the Death Valley-Mule Springs fault system, either due to hydrologic effects, or dip-slip tectonics. No resolvable interseismic deformation is detected across the Garlock fault. The Blackwater fault is associated with line-of-sight velocity of 2 mm/yr. By combining data from the ascending and descending satellite orbits, we infer that most of that strain is associated with the differential vertical motion across the fault (east side up), so that the accelerated strike-slip motion on the deep extension of the Blackwater fault is not required.
G51C-0621
Surface Deformation from ALOS Interferometry Related to the July 2006 Seismic Crisis and Dike Intrusion on Central New Britain Island, Papua New Guinea
In July of 2006 a seismic swarm struck near the Sulu volcanic range on the north coast of central New Britain Island, in Papua New Guinea. In the global Centroid Moment Tensor (CMT) catalog (www.globalcmt.org) a total of eighteen earthquakes were large enough for CMT solutions to be determined. The magnitudes of earthquakes with CMT solutions ranged from Mw 4.8 to 5.2 until July 19 when the two largest earthquakes in the swarm (Mw 5.9 and 6.4) occurred. These were also the last two earthquakes in the swarm large enough for a CMT solution to be determined. L-band radar interferometry data from Japan's Daichi ALOS satellite captured the surface deformation associated with the seismic swarm. Modeling of over 1 m of peak to peak range change deformation is consistent with intrusion of about 1 km33 of magma in a near-vertical dike with over 10 m of opening. The subduction zone beneath the study area is very dynamic, with the Solomon Sea plate subducting under the South Bismarck plate at more than 130 mm/year. Also, the volcanics in the Sulu range are some of the most elementally depleted arc volcanics on Earth. In our interpretation the dike intrusion proceeded in a WSW direction from under the Sulu volcanic range until it intersected a pre-existing fault upon which the July 19 Mw 5.9 and 6.4 strike-slip earthquakes occurred. Aftershock data recorded after July 19 with support by Geoscience Australia displays a sharp linear cutoff that aligns with the favored NW striking fault plane of the two July 19 earthquakes.
G51C-0622
InSAR Studies of Crustal Deformation Near Jakobshavn Isbrae, Greenland and Cane Creek Anticline, Utah
We will present studies of two kinds of crustal deformation phenomena using Interferometric Synthetic Aperture Radar (InSAR) technique. Jakobshavn Isbrae, one of the largest outlet glaciers in Greenland, has been undergoing significant thinning and acceleration in recent years (Thomas, et al, 2003; Joughin et al, 2004). We use InSAR to measure crustal uplift in the ice-free bedrock area near the mouth of the glacier from 2002 to 2007, caused by the removal of the ice load. We will discuss the possibility of using the crustal deformation measurement to improve the estimation of mass loss rate of Jakobshavn Isbrae. Orbital error correction using empirical models and GPS data as ground control points will also be discussed. Since 1970s, potash ore has been mined from about 3000 feet underneath the Cane Creek anticline in southeastern Utah, using a system combining solution mining and solar evaporation. The barren and arid conditions in this area are ideal for InSAR measurements. Ground coherence is well maintained, even for time spans larger than 5 years. Interferograms formed by using ERS-1/2 SAR data show that the ground surface was subsiding steadily with a rate of 10~15 mm/yr in the period of 1992 to 2002. Detailed results, including time series studies of the subsidence rate and shape and their relation to mining activities will be provided.
G51C-0623
Crustal Deformation in the Eastern Snake River Plain and Yellowstone Plateau Observed by SAR Interferometry
The Snake River Plain-Yellowstone tectono-volcanic province was created when North America migrated over a fixed hotspot in the mantle. Synthetic Aperture Radar Interferometry (InSAR) has been applied in this study to address the recent tectono-volcanic activity in the Eastern Snake River Plain (ESRP) and the southwestern part of Yellowstone Plateau. InSAR results show that crustal deformation across the tectono-volcanic province is episodic. An episode of uplift (about 1 cm/yr) along the ESRP axial volcanic zone, directly southwest of Island Park, has been detected from a time-series of independent differential interferograms created for the 1993-2000 period. Episodes of subsidence (1 cm/yr) during 1997-2000 and uplift (3 cm/yr) during 2004-2006 have been also detected in the active Yellowstone caldera, just northeast of Island Park. The detected interferometric signals indicate that deformation across the axial volcanic zone near Island Park is inversely linked to deformation in the active Yellowstone caldera. One explanation is that the inverse motions reflect a flexure response of the ESRP crust to magma chamber activity beneath the active caldera, although other interpretations are possible. The time-series of differential interferograms shows that no regional deformation has occurred across the central part of ESRP during the periods of observations, but local surface displacements of 1-3 cm magnitude have been detected in the adjacent Basin-Range province. Differential surface movements of varying rates have been also detected along Centennial, Madison, and Hebgen faults between 1993 and 2006.
G51C-0624
Shallow coseismic deformation in Western Australia observed with InSAR and seismic data
The South West Seismic Zone (SWSZ) located in Western Australia, is an area of high intra-plate earthquake activity. The area is thought to pose significant seismic hazard since the SWSZ is near to the city of Perth, a population centre of 1.5 million people, and it encompasses the source area of the magnitude 6.8 Meckering earthquake of 1968. We have undertaken an analysis of interferometric satellite radar (InSAR) observations, from the ENVISAT satellite, of a seismically active area of the SWSZ. We have observed a shallow, 1 km depth, magnitude 4.4, reverse fault earthquake near the township of Kalannie. The earthquake generated maximum line-of-sight coseismic displacements of 28 mm, visible in both descending and ascending passes. We reduce atmospheric artifacts through a time series analysis of the InSAR data and develop an analysis strategy which deals with transient signal stability associated with agricultural activity in the study area. This is the first observation of a coseismic displacement field associated with an Australian earthquake using modern satellite geodetic tools. It provides important constraints on the earthquake hypocentre and source mechanism that can be used to calibrate techniques for determining earthquake magnitude and location that are used in routine earthquake monitoring of the SWSZ. We make a comparison of the InSAR determined earthquake mechanism to seismic observations of the event.
G51C-0625
InSAR Identifies Mine-Dewatering Associated Bedrock Compaction and Subsidence in North- Central Nevada
During the last decade, InSAR has been used extensively for the delineation of aquifer-system response to heavy groundwater pumping. A number of studies have demonstrated the vastly improved spatial resolution afforded by InSAR relative to traditional surveying techniques in detecting groundwater-related effects, including subsidence. This has allowed for further understanding of the complexity of subsidence bowls and the role of secondary factors such as structure, aquifer material properties and other previously unforeseen factors. In the western U.S., ground subsidence related to mine dewatering is a common occurrence due to the very large volumes of water (as high as 100,000 acre-ft/yr) that are typically pumped in order to lower the local groundwater table to facilitate the excavation of open pit and underground mines. Several gold mines located along the Carlin Trend of Central Nevada have produced distinct InSAR-identified subsidence signals of greater aerial extent and magnitude than most municipal groundwater signals, including signals partly or entirely within bedrock. One signal in particular shows a minimum of 54 cm of cumulative dewatering related subsidence between June 1, 1992 and September 21, 2000. Our study has produced many (>50) interferograms, each covering different time intervals, allowing a better understanding of how the subsidence signal has evolved in response to varied pumping rates from dewatering wells. Since the spatial resolution of the InSAR is much better than that of the monitoring well locations, the complexity of the signal is better delineated. The aerial extent of the subsidence feature is impressive as it extends as far as 20 km away from the location of the extraction wells used for dewatering. The area of maximum subsidence correlates well with the area of maximum groundwater drawdown, however the subsidence signal extends well beyond (as much as 8-10 km) the observed groundwater drawdown pattern. This suggests a much deeper zone of compaction and/or subsidence. The large aerial extent is likely a result of the fact that the vast majority of the pumping is from the deeper bedrock aquifer, with very small amounts of pumping from shallower siltstones and unconsolidated basin fill. The geology within the deformation signal is very complex. The dewatering is occurring in deep carbonates which are overlain by varying thicknesses of basin fill, volcanics, siliceous siltstones and mudstones and other limestone units. Close inspection of these units in the main open pit as well as a nearby underground mine suggests that while many of these units are highly fractured, most of the fractures have been healed with silica or are so tight that minimal fracture closing is possible. This suggests another mechanism causing the ground surface to subside, including compaction of intact bedrock. Groundwater related bedrock subsidence of this scale is rarely, if ever, observed, and therefore, poorly understood. Ongoing work at this site is focused on better understanding the mechanics of the observed bedrock compaction/subsidence, and possible implications to other high volume groundwater pumping sites.
G51C-0626
Investigating the Creeping Segment of the San Andreas fault using a Maximum Likelihood Persistent Scatterer Technique
Numerous new methods that use multiple SAR interferograms have been developed recently to study the temporal characteristics of deformation in a region of interest. Persistent scatterers (PS) approach relies on identifying a network of pixels in the interferogram whose scattering properties vary little with time. Various PS- InSAR methods have been proposed and have been shown to work reliably in urban environments. The Stanford Method for PS (StaMPS) was the first method developed to extend the scope of PS-InSAR, to work effectively in vegetated regions. The maximum likelihood approach to PS selection (also developed at Stanford) is a new method that has been shown to be effective in identifying PS in the vegetated areas in the Bay Area in California, USA. The primary advantage of both these methods are that they do not assume a model for the deformation pattern. Ability of the maximum likelihood method to identify a reasonably dense PS network in vegetated regions, where conventional InSAR and other PS-InSAR algorithms failed, makes it a powerful tool for estimating the deformation time-series in heavily decorrelated regions. This method identifies PS by estimating the most likely Signal-to-Clutter Ratio (SCR) by comparing the time-series of interferometric phase of pixels in a stack of interferograms with a statistical model describing the interferometric phase. We will present the results from maximum likelihood PS-InSAR analysis of the creeping section of the San Andreas fault in central California, one of the first areas to which this new technique has been applied. This section of the fault is known to creep at rates in excess of 20 mm per year. Geodetic measurements up to now ( e.g. from creepmeters, GPS) have tended to have poor spatial and/or temporal resolution. A stack of multiple ERS interferograms covering the creeping segment between 1992 and 2001 gives good spatial information about surface deformation, but the stacking technique assumes linear displacement gradients over time. The PS approach offers the opportunity to generate time series of surface displacement at a potentially large number of points, which may provide important clues about the mechanics of creep at depth.
G51C-0627
Application of Maximum Likelihood PSInSAR to Subsidence Monitoring in the Geothermal Fields of Imperial Valley, California
Persistent Scatterer (PS) InSAR methods are among the most successful new methods using a stack of interferograms to extract deformation time series in regions where traditional InSAR is limited. In particular, the PSInSAR technique performs significantly better in vegetated areas. We have been developing a Maximum Likelihood PS (ML-PS) method in an attempt to improve on earlier PS techniques, such as StaMPS (Hooper et al., 2003) and Permanent Scatterers Technique (Ferretti et al., 2000). The ML-PS method works by estimating the most likely signal-to-clutter ratio (SCR) of each pixel by comparing the interferometric phase time-series against mathematical models describing the interferometric phase as a function of the SCR. We have already successfully used the ML-PS method in the vegetated regions of the Bay Area in California (Shanker and Zebker, IGARSS 2007). Here we extend this work to estimate the surface deformation, mostly subsidence, in the Imperial Valley region of southern California. The reasons for this subsidence may be tectonic, as well as related to geothermal production in three geothermal fields – Salton Sea, Heber, and East Mesa. Of these, Salton Sea and Heber are inundated with agricultural fields, rendering conventional InSAR methods ineffective. While surface subsidence is a well known phenomenon in geothermal fields all over the world, it has not caused significant problems in the Imperial Valley region. However, it may increase in the next decade due to enhanced geothermal production, and its monitoring is thus of increasing importanc. We will present 1992-2000 results based on the analysis of ERS SAR data from the WINSAR archive. These results will be compared with 2004-2007 results from the analysis of ENVISAT data, using both ascending and descending tracks. It will be demonstrated that our ML-PS method identifies a denser network of PS in the region compared to the other known PS methods. The results from the PSInSAR analysis will be compared with leveling data provided by the geothermal operators. We intend to demonstrate the effectiveness of the new PS-InSAR method to monitor the deformation due to geothermal extraction in vegetated regions.
G51C-0628
The Use of Permanent Scatterer InSAR in the Detection and Analysis of Aquifer-System Response to Long-Term and Seasonal Pumping and Recharge
The application of interferometric synthetic aperture radar (InSAR) studies to hydrogeological problems has advanced rapidly during the last decade, and it is now applied routinely to a wide range of groundwater resource issues including aquifer-system response and resource management. Permanent scatterer InSAR (PSInSARTM) provides a new high-resolution methodology for detecting and precisely measuring long-term and seasonal aquifer-system response to pumping and recharge. In contrast to the conventional InSAR methodology, the permanent scatterer (PS) methodology utilizes coherent radar phase data from thousands of individual radar reflectors on the ground to develop displacement time series and to produce velocity field maps that depict time-dependent aquifer-system response with a high degree of spatial detail. In this study, we present the results of a prototype study in Las Vegas Valley, Nevada, that demonstrate how the PS methodology can be utilized in heavily pumped groundwater basins of the arid western US to analyze aquifer- system response to long-term and seasonal pumping. We used 50 ERS-satellite and 19 ENVISAT-satellite acquisitions to develop a series of velocity field maps of the valley for the 1992-1996, 1996-2000, and 2003-2005 time periods that were then compared to water-level change data for the same time periods. The PS results show that despite rising water levels associated with an artificial recharge program, long-term, residual, inelastic aquifer-system compaction (subsidence) is continuing in several parts of the valley. In other areas of rapidly recovering water levels, however, long-term subsidence has been arrested and locally reversed as long-term elastic recovery of the aquifer-system occurs. In addition, the short-term, seasonal, elastic responses to alternating pumping and recharge cycles were segregated from the long-term trends and analyzed for spatial and temporal patterns. The results show oscillations in which the maximum seasonal responses are associated with the late stages of the annual artificial recharge cycles, and that similar seasonal subsidence signals are related to summer pumping cycles. This differentiation of the seasonal response through the use of PS time series data further allows the estimation of elastic and inelastic skeletal storage coefficients, providing a basis for future work that could characterize the storage properties of an aquifer system with a high degree of spatial resolution.
G51C-0629
Water Vapour Bias in Measuring Interseismic Strain Accumulation With InSAR for the Altyn Tagh Fault, N. Tibet
The slip rate of the left-lateral Altyn Tagh Fault (ATF) of Northern Tibet is poorly known and controversial. Geologic rates from Holocene and long-term offsets range from 10 to 30 mm/yr. Geodetic rates from GPS are towards the low end of this range (around 10 mm/yr). SAR data have been acquired over this region by the ERS satellites through the nineties and continue today with the ENVISAT platform. These datasets provide an opportunity to measure interseismic strain accumulation on faults. However, InSAR measurements vary from 5 mm/yr for the western ATF (Wright et al., 2004) to 17 mm/yr for the central ATF (Peltzer et al., AGU Fall Meeting 2006). An ongoing challenge for the accuracy of this geodetic technique is the variability of tropospheric water vapour, which induces unwanted phase delays. This is particularly pronounced in the case of the Altyn Tagh Fault system, which exhibits a 2-4 km step in relief between the Tarim Basin and Tibetan Plateau. We investigate the effects of water vapour on the inferred slip rate. An analysis of ERS data has highlighted a bias from the non-uniform distribution of SAR acquisitions through the year. Due to the lack of contemporaneous independent measurements of water vapour for ERS data, we attempt to mitigate tropospheric water vapour errors by solving for a linear fit with topography. A network of 59 interferograms is used to correct for orbital errors and water vapour, before inverting for a slip rate. We invert for a buried fault using a simple elastic dislocation model and assume pure strike-slip motion with no component of uplift. To determine the error in the calculated slip rate, 100 synthetic datasets are created and perturbed with characteristic orbital and atmospheric noise. Using ERS data at 85°E we find a slip rate of 10 ±1σ 5 mm/yr with the water vapour correction, and 35 ±1σ 9 mm/yr without. Because of the large impact of the water vapour on the result, we tested for the effect of the temporal distribution of SAR acquisitions by systematically shifting the epochs through the year, using modelled weather data from the European Centre for Medium-Range Weather Forecasting to simulate the effects of tropospheric delay. On repeating the Monte Carlo analysis, a clear seasonal bias is retrieved. In the worst cases, slip rates can be under- or over-estimated by as much as 15 mm/yr if the water vapour is not accounted for. When we solve for the water vapour contribution based upon height, the bias is removed.
G51C-0630
The application of multi-temporal, multiple-satellite SAR data for the analysis of backscattering variations, InSAR-derived water-level changes over swamp forests, and subsidence over Southeastern Louisiana
We use multi-temporal European Remote Sensing Satellite 1 and 2 (ERS-1/2), Environment Satellite (ENVISAT), Canadian RADARSAT-1, and Japanese ALOS Synthetic Aperture Radar (SAR) images for ecological, hydrological, and geological studies over Southeastern Louisiana. First, we investigate the seasonal changes in SAR backscatter and interferometric coherence, and their associations with land covers; temporal variation of radar backscattering signal during leaf-off season shows high correlation with the normalized difference vegetation index. Second, we demonstrate the use of both C-band and L-band SAR images to measure changes in water-level beneath swamp forests composed of moderately dense trees, at a vertical accuracy and spatial resolution that is not possible with the current gauge-based measurements. Third, we apply the conventional InSAR and the Persistent Scatterer InSAR techniques to map land surface subsidence over New Orleans and its surrounding area. The comparison of measured subsidence patterns shows certain discrepancies probably due to atmospheric delays in this humid area. Our study demonstrates the importance of SAR data for understanding this coastal flood zone and the associated ecological, hydrological and geological processes.
G51C-0631
Simulation-based impact of DESDynI mission duration and repeat time for postseismic processes
The DESDynI mission detailed observing scenario is influenced by the expected science return, balancing the needs of several disciplines. From the standpoint of bettering our understanding the earthquake cycle, a key advance will come from the ability to observe the postseismic period and discriminate among possible process models. Note that different models lead to different stress transfer calculations, that affect the changing picture of earthquake risk in the region. We generated 1600 synthetic earthquakes, in the form of a single sample composite measurement that has a line of sight coseismic displacement, followed by a linear combination of a logarithmic afterslip function and an exponential decay relaxation function. The coseismic slip, the ratio of coseismic to postseismic afterslip, the ratio of coseismic to the postseismic relaxation amplitude, and the time constants for the postseismic processes were generated from random distributions that were fit to a literature search of interesting earthquakes. A time series with parameter partials was generated for each synthetic event, and transformed into estimation error bars given that each view produced a measurement of motion with 1 cm error. An event is considered resolved only if the slip amplitudes of both afterslip and relaxation is estimated to a relative error of under 0.5. If we have six months of observations after an event, going from 8 to 14 day repeat means losing 18 per cent of the resolved events , going to 45 days means losing over 99 per cent. If we consider two years of observation after an event, going from an 8 day repeat to 45 days means losing 33 per cent of the resolved events.
G51C-0632
Measurement of Surface Deformation using a Ground-based Real Aperture Interferometer
Differential interferometry has proven as a technique to be very useful for the measurement of surface deformation relating to geophysical processes such as earthquakes, landslides, volcanoes, glaciers. Up until recently these measurements have been performed from data derived from space borne sensors such as ERS, Envisat, and Radarsat. These space borne sensors have the advantage of obtaining large area acquisitions but are limited in a number of ways. Most serious is the lack of dense temporal sampling due to long repeat times. Also due to the fixed orbit track, the number of views of the scene is limited. Ground based interferometry (GBI) has demonstrated the capability to continuously map the motion of landslides, glaciers, at mm scale. The advantages of ground-based observation include on-demand availability, the potential of continuous observations, and flexibility in selection of the observation geometry with very small baselines, high spatial resolution, and the potential to suppress atmospheric phase variations by averaging by acquisition of multiple images. GBI implementations up to this time have utilized a small antenna traveling along a linear rail. We have developed a new Terrestrial Radar Interferometer (TRI) operating at 17.2 GHz and utilizing a azimuthal rotating interferometric array of real-aperture antennas Because the two SLC images are created simultaneously, we can create an elevation model of the entire scene, even for scatterers that are incoherent. The scope of this paper is to describe the system and performance for generating height and deformation maps. We show some our first results mapping motion of the Rhône Glacier in Switzerland and the Tessina landslide near the city of Belluno in Northern Italy.
G51C-0633
Deformation Measurements for the September 2005 AFAR Rifting Event from Sub-Pixel Correlation of SPOT Images
The rifting of the ~60km long Dabbahu segment of the AFAR rift, associated with a large number of Mw=3.5- 5 earthquakes and a volcanic eruption, is the largest such land event in the era of satellite geodesy. We matched at a sub-pixel level SPOT4 10m optical satellite images spanning the event in order to measure horizontal displacements in the rupture zone. The latest improvement of the technique has removed the CCD artifacts of the sensor and by averaging across a swath we obtain measurement uncertainties of the order of ~20cm (1/50th pixel). The displacements show a maximum opening of up to 8m, agreeing well with the horizontal components of a 3D deformation field estimated from SAR interferograms and radar range (accurate to ~2m) and azimuth (accurate to ~60-70cm) offsets (Wright et al., 2006). Large deformations in the rift zone itself causes decorrelation in the interferogram and loss of data. Using horizontal offsets from optical matching, we are able to determine an enhanced 3D deformation field, particularly in the area of maximum rupture, and hence an improved elastic dislocation model of the event.
G51C-0634
Paleoshoreline Record of Crustal Uplift in the Dry Valleys Region, Antarctica: A Pilot Study Using ALS Digital Elevation Data
In much of the world, key records used for mapping and modeling glacial-isostatic crustal motions come from raised shorelines and isolation basins. Such records are extremely scarce in Antarctica. A unique digital elevation data set was acquired by NASA's Airborne Topographic Mapper (ATM) system during the 2001-2002 austral summer field season. This Airborne Laser Scanning (ALS) digital elevation data was used to map lake paleoshoreline elevations and tilts in the Dry Valleys region of Antarctica, providing a unique record of vertical crustal motion spanning the last 15,000 years. Laser points were derived by NASA and the computation and verification of Digital Elevation Models (DEMs) was completed by Ohio State University in 2003. Resulting DEMs have 2 meter horizontal resolution, sufficient for discerning lake-surface geomorphic features that were horizontal at deposition. DEM data were filtered to highlight paleoshoreline profiles and delta profiles, where multiple delta deposits were available from a single lake level. Elevation data were extracted along the digitized profiles. Changes in elevation along the length of these profiles were then used to define regional tilt angles and directions, reflecting crustal motions since the time of deposition. Finally, derived tilts were linked with C14 age data from previous studies, allowing calculation of rates of crustal motion over the past 15,000 years. This record of crustal uplift can be integrated with GPS data acquired in the same region to model glacio-isostatic motion due to ice mass change and to constrain thickness and rheological properties of the crust and mantle. Results from this study represent the first application of paleoshoreline tilt data mapped from ALS data in Antarctica.
G51C-0635
Monitoring Earth Surface Dynamics With Optical Imagery
Optical images can be used to measure accurately a variety of Earth surface processes such as co-seismic ground deformation, ice-flow, landsliding and sand-dunes migration. Although the technique of correlating multi- temporal images is not new, it is not widely used yet due to technical limitations - mainly geometric distortion of the images induced by the imaging system, biased correlation techniques, and implementation difficulties. Most of these obstacles were overcome by recent methodological advances implemented in a user-friendly software package, COSI-Corr, which allows for automatic and precise ortho-rectification, co-registration, and subpixel correlation of pushbroom satellite and aerial images. The procedure does not require external information such as GPS measurements of ground control points, and is solely based on the knowledge of the topography and on the ancillary data provided with the observing platform. In particular, we take advantage of the availability of accurate digital elevation models with global coverage (SRTM). Sub-pixel change detection, i.e. correlation, is then applied on the set of ortho-images produced. COSI-Corr makes it possible to measure local displacements between temporal series of images, possibly acquired by different instruments and at different resolutions, with accuracy of the measurements on the order of a small fraction of the nominal images' resolution. We apply this methodology to the measurement of the horizontal coseismic displacement field induced by the Mw 7.1 1999 Hector Mine earthquake, California, using a 10-m SPOT 4 pre-earthquake image and a 15-m ASTER post-earthquake image. We illustrate the potential of this approach to measure glacier flow, and present the horizontal displacements in the Mer de Glace area (Alps), over 26 days derived from SPOT 5 images. Landsliding is also investigated on the La Valette landslide (southern French Alps), and we present a dense measurement of the cumulative horizontal displacement over eleven months, using SPOT 5 images. Finally, we demonstrate that sand dunes migration can also be monitored. A dense and complete picture of the displacement of the sand dunes over the Great Colorado Sand Dunes national park is obtained from the correlation of two ASTER images acquired in 2000 and 2003. http://www.tectonics.caltech.edu/slip_history/spot_coseis/