G51B-0076 0800h
Crustal Deformation in Iceland: Constraints on Tectonic and Magmatic Processes from InSAR observations
Crustal deformation events in Iceland in a variety of tectonic settings have been recognized using ERS1 and ERS2 images provided by ESA, including: (1) Intrusions in the Eyjafjallajökull volcanic system. Images spanning 1993-2000 identify considerable surface deformation in an area south of the Eyjafjallajökull icecap. The intrusive events (occurring in 1994 and 1999) have also been detected by tilt and GPS campaign measurements, as well as high seismic activity. Modeling based on InSAR data suggest a more complex source geometry than previous work based on GPS and seismic data. (2) Earthquake faulting in the SISZ due to seismic activity in June 2000 has been detected in several images. On June 17, and June 21, 2000 two Mw 6.5 earthquakes ruptured N-S striking faults in the SISZ. Joint inversion of InSAR and GPS data indicates that the two events activated faults 15 km long extending to about 9 km depth. Maximum slip, reaching more than 2 meters in both events, is concentrated in the upper crust, from the surface to 5-6 km depth. (3) Deformation due to dynamically triggered earthquakes on the Reykjanes Peninsula, about 80 km to the east of the main event in the SISZ (June 17, 2000 Mw 6.5 earthquake). Inverse modeling of the InSAR data estimates the deformation to originate from a Mw 5.8 and a Mw 5.3 event, when assuming uniform slip on two simple rectangular fault patches. (4) Subtle surface deformation signal in the vicinity of the main earthquake faults active in the June 2000 SISZ sequence have been documented in InSAR images. The deformation signals correlate well with water-level changes in geothermal wells and have been interpreted as poro-elastic rebound following the SISZ 2000 earthquakes. (5) An eruption at Hekla volcano began on February 26, 2000. Short-term precursory seismic activity was detected about one hour before the eruption started. Initially, a 6-7 km long eruptive fissure opened up along most of the Hekla ridge. Deformation due to the eruption is seen in a series of interferograms. The displacements appear to be the result of dike opening as well as subsidence due to deflation of a deep-seated magma chamber. (6) Surface inflation due to inflow of magma in the Hengill area can be seen in images spanning 1993 to 1998. The uplift signal can be explained by an expanding Mogi-source at 7 km depth, with 2-cm/year inflation rate. Persistent seismicity during 1994 to 1998 was associated with the widespread uplift. (7) Long-term subsidence in the Askja caldera has now been recognized not only by tilt and GPS, but also in InSAR images. A series of interferograms shows continuous subsidence, with the size of the deformation signal scaling well with the time span of the images. The subsidence can be partly related to cooling of a magma chamber. (8) Readjustment of the spreading segment at Krafla has been detected in InSAR images spanning 1992 to 2000. Subsidence occurs above an inferred shallow magma chamber, which fed events during the 1975 to 1984 rifting period. The subsidence is elongated along the spreading axis, which is interpreted to be due to cooling contraction and ductile flow of material away from the spreading axis. A wide-spread uplift signal of about 1 cm/yr has however been recognized to the north, and appears to be due to recharging of magma into a deep seated source. All the studies have benefited from images contributed by ESA PI contracts.
G51B-0077 0800h
Four-Component Borehole Strain Meter: Observation and in-situ Calibration
Borehole strain meters are a key component of some important geo-scientific projects, such as PBO, to monitor seismic and aseismic tectonic strain phenomena. Observation using a four-component borehole strain meter, namely Ouyang borehole strain meter, has been kept continuous at Changping station, Beijing, for years. The plane strain changes are obtained at the depth of 120m and from 4 horizontal measurements, spaced 45 degrees apart, of the radial deformation of the borehole in which the instrument is installed. The challenge is that, according to the theory of elasticity, the sum of any two measurements perpendicular to each other should be the same as related to areal strain. The observation at Changping agrees pretty well with this rule and, with a relative in-situ calibration correction to the transducer factors based on the rule, the agreements can be yet much improved. Since the transducers were arranged well in the orientations of North, East, North West and North East, respectively, instrument shear strains can be simply given as the differences of the two correspondent perpendicular measurements. By applying theoretic Earth strain tide as a reference signal, in-situ absolute calibration can be carried out and the proportionality constants c and d, and the orientation error as well, can be calculated separately. Fore-component borehole strain meter has the advantages of giving more accurate and more reliable data for Earth strain and of easier processing as compared to three-component borehole strain meter.
G51B-0078 0800h
Terrain Change Detection Using ASTER Optical Satellite Imagery Along the Kunlun fault, Tibet
Terrain changes are manifested in satellite images as pixel offsets, which represent the apparent difference in the position of corresponding pixels in two time-separated images of the same portion of the Earth's surface. We present terrain change detection results using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imagery. The change detection methods employed are Fourier analysis, image window cross-correlation ("imageodesy"), and a wavelet analysis. These methods were applied to the detection of seismic displacement due to the November 14, 2001 Kokoxilli earthquake. During this Ms = 8.1 event, the Kunlun fault experienced a maximum of 16.3 m of displacement. Three ASTER image pairs along the Kunlun fault were used, each with different time separation windows. Each time separation window represents a different time interval, from two years to two months. Our results show that terrain change detection was most successful using the Fourier and wavelet techniques. The Fourier analysis detected left-lateral slip of 4.5 m along a fault oriented $270\deg$ in the proximal area of the Kunlun fault. These results are in good agreement with field observations. Wavelet analysis was very effective at delineating fault scarps caused by the 2001 Kokoxili earthquake.
http://www.geo.utep.edu/pub/schiek/Thesis.pdf
G51B-0079 0800h
Ambiguity Resolution Constraints In The Estimation Of Very Long Baselines By GPS In The Global Network Solution
A new global network solution was adopted in the estimation of very long baseline lengths from Hyderabad IGS Permanent GPS Station to other select IGS stations in and around Indian Plate. As part of on-going study on Indian Plate Kinematics, very long baseline lengths were estimated using the data from IGS select stations, including Hyderabad, for the time spanning 9 years from September 1995 to May 2004. Since some of the estimated baseline lengths are more than 6000km, it is a common knowledge that the ambiguity parameters have to be estimated as real integer values, instead of being `fixed' to integer values. Use of ionosphere-free linear combination of two frequencies has helped to remove the first order ionospheric noise. But this results in an accentuation of the non-dispersive noise. The lengths of the baselines of our network, that are between 2000 and more than 6500 km, make ambiguity fixing impossible. All the solutions presented in this study leave the ambiguity non-fixed. In the data analysis for long-term precision of continental scale interstation vectors measured with GPS, the L3 ionosphere-free combination was used with wide-lane ambiguity fixing for baseline lengths up to 2000km.When it is extended to the baseline lengths beyond this and more than 6500km, evidently the level of accuracy deteriorates, as the ambiguity parameters have large aposteriori rms errors. The strategy adopted, when measuring very long baseline lengths to pre-eliminate the ambiguity parameters estimated as real numbers and the normal equation matrix inversion, are discussed in this presentation. The length dependent accuracy deterioration is also discussed and shown for the entire data set.
G51B-0080 0800h
SLR Observations of ICESat
Precision orbit determination (POD) for ICESat is performed primarily using GPS data from on-board instrumentation. However, SLR observations provide important verification of GPS-based results. Additionally, SLR operations allow the testing of the logistics of target-specific observing restrictions, in cooperation with the International Laser Ranging Service (ILRS). With some missions, target specific restrictions on SLR observations become an important issue for routine laser ranging operations. For SLR observations of ICESat, SLR stations must not shoot "up the barrel", with the possibility of harming on-board instrumentation. Several ILRS stations, notably MLRS, Zimmerwald and the MOBLAS stations, have automatic elevation-initiated laser cut-off software. They have been invited to range to ICESat under the restriction that ranging not be performed when ICESat has an elevation greater than 70 degrees, as seen from a station. Further, ICESat, at times, performs off-nadir pointing. Thus, even though ICESat may be at an elevation less than 70 degrees as seen from a station, it might still be possible for it to shoot "up the barrel". Communications must exist between the ICESat operations center and cooperating stations to assure that ranging is not performed when ICESat may be pointed in the direction of any particular station. Finally, because of the "spottiness" of the potential SLR data set for ICESat, based upon operational outages, and the fact that only a sub-set of the SLR network is used for ICESat ranging, predictions that are based only upon previously obtained SLR data might possibly not satisfy accuracy and precision requirements. To that end, we prepare standard SLR predicts using the data from ICESat's on-board GPS navigation files. In this poster we will expand upon all of these points, present some of the pit-falls encountered, review the SLR data obtained, and assess the successes.
G51B-0081 0800h
Orbit and Gravity Determinations Using ROCSAT3/COSMIC GPS Data: Status 2004
The ROCSAT3/COSMIC (RC) mission is scheduled to be launched in late 2005 and contains a geodetic element in the mission. Each of the six satellites of RC is equipped with a POD GPS antenna which yields data for precise orbit and gravity determinations. In view of the large number of satellites and orbital planes, simple satellite's simple geometry (cylindrical) and a long life span (expected 5 years), the geodetic results from RC are particularly suited for static and time-varying gravity research. This paper reports the status of our geodetic research related to the RC mission as of 2004. A computer program package, called CTODS, is developed for precise orbit and gravity determination. In CTODS, satellite perturbing force models are based on the IERS2000 standards and the results are validated using the results from NASA/GSFC's GEODYN II program. A one-step method, based on a GPS-preprocessing package and GEODYN II, was used to determine CHAMP orbit and gravity. In a two-step approach, one year of CHAMP precise positions, which were determined using a pure kinematic method, were used as satellite tracking data to compute weekly gravity harmonic coefficients. Simulation results using an analytical orbit theory show that RC-recovered gravity contains prominent gravity changes during the 1997-1998 El Niño event.
G51B-0082 0800h
The Campaign GPS Component of the Plate Boundary Observatory (PBO): New Tools, New Strategies and New Opportunities to Support EarthScope Investigations
The UNAVCO Facility is charged with implementing the campaign GPS component of the Plate Boundary Observatory (PBO) to support EarthScope investigators through a pool of approximately one hundred mobile GPS systems. In contrast to the PBO continuous GPS network, the PBO campaign systems are designed for temporary deployments with periods ranging from several minutes to several months per site. This allows researchers to conduct spatially and temporally focused investigations into a wide range of phenomena, including volcano monitoring, post-seismic deformation monitoring, and ground control for airborne LIDAR surveys. A standard PBO campaign system consists of a Topcon GB-1000 dual-frequency GPS receiver, a Topcon PG-A1 compact GPS antenna, an 18 Ah battery, cabling, a portable and waterproof Pelican case enclosure, and a Tech 2000 GPS antenna mast or tripod and tribrach. Available ancillary equipment includes solar panels, additional batteries, enclosures and mounting hardware. Communications equipment such as radio modems and cellular modems are also available to allow remote data retrieval during longer term deployments. We present an overview of the PBO campaign equipment available to investigators, technical specifications of the system, examples of current and planned EarthScope research projects utilizing the campaign equipment, and a hands-on demonstration of a PBO campaign system.
http://pbo.unavco.org/faqs/Campaign_Equipment_PBO_FAQ.html
G51B-0083 0800h
Subsidence induced by ground-water withdrawels across the Wasatch Front, Salt Lake Valley, Utah
Interferometric Synthetic Aperture Radar (InSAR) imagery of the Salt Lake Valley shows a northwest-trending, 12- x 17-km elongate subsidence bowl, centered on Salt Lake City, that has an annual subsidence rate of of 12 mm/year and seasonal uplift of ~30 mm. Radar imagery from the European Space Agency's ERS satellites (1992-2000) shows that the subsidence has been persistent over this period, with >100 mm of cumulative line-of-sight range change in the valley. On the basis of water-well records and radar imagery, the onset of the subsidence likely predates the 1992 launch of the ERS-1 satellite. The seasonal uplift has been observed in a few fall interferograms, is confined to the southern portion of the basin, and has a maximum magnitude of 30 mm. The western, southern, and eastern margins of the deforming bowl, as observed in the interferograms, are distinctly linear and presumably indicate impermeable or semi-permeable barriers to ground-water flow across faults in the Wasatch fault system. A preliminary evaluation of ground-water levels throughout the Salt Lake Valley region suggests a correlation between the seasonal and annual deformation and the location and timing of ground-water withdrawels. Subsidence of this magnitude will produce both seasonal and long-term human-induced horizontal strain gradients that will need to be taken into account when assessing seismic hazard associated with the low slip rates along the heavily populated Salt Lake segment of the Wasatch Front.
G51B-0084 0800h
Precise positioning of VSOP2 satellite by delta-VLBI method
Following the success of the VLBI Space Observatory Program (VSOP), a next generation space VLBI mission, currently called VSOP2, is being planned. For VSOP-2, higher observing frequencies (8GHz, 22GHz and 43GHz), cooled receivers, increased bandwidths and a larger telescope diameter will result in gains in resolution and sensitivity by factors of 10 over the VSOP mission. The possibility of including a rapid slewing capability for the spacecraft is also being pursued, so that observations using the phase-referencing technique will enable the sensitivity to be improved even further. For phase-referencing observations, orbit accuracy of about 3 cm is required. VSOP2 will have a highly elliptical orbit with apogee altitude of 25000 km. Orbit determination of few-cm accuracy could be achieved by using GPS receivers inside the GPS satellite orbits. Delta-VLBI method could connect position and velocity within the required accuracy over period of time when GPS positioning are unable to provide good solution. Delta-VLBI positioning system and error estimation are shown in this paper.
G51B-0085 0800h
The Hazard Analysis of Debris Flow by a Neural Network and Digital Terrain Model: A Case Study in Taiwan
Taiwan is a narrow island. Due to the movement of the plate tectonics, the mountain ranges are almost in N - S direction. On the island, there are a lot of mountains, but few plains. Because of the rapid development on economies, the plains are nearly used-up. So people are trying to develop the mountainous land. However, when the typhoon, heavy rain, or earthquake occurred, there triggers the catastrophic events, such as the landslide and debris flow. Among these catastrophes, the debris flow is the most horrified and it happens frequently year after year. Thus, how to prevent the debris flow and pass this information to warn the local residents becomes an urgent matter. The most reliable method to identify the hazardous debris flow is to investigate in the field. Because the change of the factors, the debris flow may happen. So it will need a long-term monitoring system. The requirement of the manpower and financial resources will increase significantly. Although there are much studies on applying the GIS to the debris flow problem, but it's still difficult to become a practical tool due to the data gathering and law limitation. If a fast-accurate and self-recognized computer model is available, this will save the time and efforts. In this study of debris flow by using the neutral network and digital terrain model, we select the Chen-Yu-Lan River in Nantou (middle of Taiwan) as an area for study. The debris flow caused in 2001 right after the TORAJI typhoon. Using the GIS software, the MapInfo, which is much simple to get the numerical data from digital terrain model. We have firstly used the 15 factors to start the training. We obtain a successful ratio of about 88%. There are some areas can't be explained. We believed it is caused by the other factors of debris flow that weren't included. The geoscientific factors are important. However, because of the resolution of present-available geological data don't reach the standard of this study. Therefore, they are skipped. Other relative data, such as the area of tumble, and density of vegetation etc. are not available at the present database.
G51B-0086 0800h
A Geometrical Geodesy Package for {\it Mathematica}
We have developed a geometrical geodesy library suite written in {\it Mathematica}. This suite contains functions defining geodetic datums, geodetic reference ellipsoids, linear and angle units found in surveying and geodesy, four major coordinate systems (geodetic, Earth-Centered Earth-Fixed Cartesian, local Cartesian, and projected) and the transformations between them. Also defined are functions for measurement reductions, the forward and inverse geodesy problems, and the major cartographic projections. We believe this package to be the most complete and extensive geometrical geodesy package that exists. It comes with full documentation and is free of charge. This presentation will introduce {\it Mathematica}, provide an overview of the library suite, and present several demonstrations of its use.
G51B-0087 0800h
Reconstructing 3-D Ship Motion for Synthetic Aperture Sonar Processing
We are investigating the feasibility of coherent ping-to-ping processing of multibeam sonar data for high-resolution mapping and change detection in the deep ocean. Theoretical calculations suggest that standard multibeam resolution can be improved from 100 m to ~10 m through coherent summation of pings similar to synthetic aperture radar image formation. A requirement for coherent summation of pings is to correct the phase of the return echoes to an accuracy of ~3 cm at a sampling rate of ~10 Hz. In September of 2003, we conducted a seagoing experiment aboard R/V Revelle to test these ideas. Three geodetic-quality GPS receivers were deployed to recover 3-D ship motion to an accuracy of +- 3cm at a 1 Hz sampling rate [Chadwell and Bock, GRL, 2001]. Additionally, inertial navigation data (INS) from fiber-optic gyroscopes and pendulum-type accelerometers were collected at a 10 Hz rate. Independent measurements of ship orientation (yaw, pitch, and roll) from the GPS and INS show agreement to an RMS accuracy of better than 0.1 degree. Because inertial navigation hardware is susceptible to drift, these measurements were combined with the GPS to achieve both high accuracy and high sampling rate. To preserve the short-timescale accuracy of the INS and the long-timescale accuracy of the GPS measurements, time-filtered differences between the GPS and INS were subtracted from the INS integrated linear velocities. An optimal filter length of 25 s was chosen to force the RMS difference between the GPS and the integrated INS to be on the order of the accuracy of the GPS measurements. This analysis provides an upper bound on 3-D ship motion accuracy. Additionally, errors in the attitude can translate to the projections of motion for individual hydrophones. With lever arms on the order of 5m, these errors will likely be ~1mm. Based on these analyses, we expect to achieve the 3-cm accuracy requirement. Using full-resolution hydrophone data collected by a SIMRAD EM/120 echo sounder we are applying the 6 components of ship motion to correct the phase center of each hydrophone. Successive pings will be analyzed for phase coherence.
G51B-0088 0800h
Radar Interferometry Reveals Underground Salt Leaching of Anthropogenic Origin in a Saharan Oilfield
Local to regional-scale ground subsidence due to underground disturbances of anthropogenic origin, such as oil or water pumping or mine collapse, represent significant environmental hazards. Radar interferometry has proven to be an essential tool for identifying and monitoring such processes. Here, we report on a case of ground subsidence at an oil field in Algeria (Ouargla area) following a well accident. In 1986, a 250 m-wide ground collapse appeared at the abandoned OKN32 oil-well near the town of Ouargla in the Sahara desert. It is hypothesized that a break in the well casing allowed for deep artesian water to reach a subsurface salt layer, which lead to salt dissolution, the formation of an underground cavity, and intense pollution of a shallow aquifer used by the local population for irrigation and drinking. We used 22 ERS images spanning from 1992 to 2000 to investigate the temporal and spatial evolution of the ground subsidence associated with this process. In particular, we aimed at quantifying the size of the underground cavity and whether or not it still continues to grow. Although no information was available on the location of the accident (or on any of its characteristics), we found a circular subsidence area clearly correlated with the OKN32 oil field. Its diameter spreads from 900 m in 1993 to about 1300 m in 1996, with a total subsidence of up to 20 cm over that time period. The subsidence rate decreases gradually from 1993 to 1996 and stops after that date, suggesting that the process has healed at depth. Preliminary calculations indicate that about 80,000 cubic meters of salt have been leached and transported to the shallow aquifer.
G51B-0089 0800h
Long Baseline Tilt Meter Array to Monitor Cascadia's Slow Earthquakes
Five biaxial Michelson tilt meters are currently being installed in the Puget Lowlands near Seattle to monitor dynamic tilt changes accompanying episodic slow earthquakes that occur at 20-40 km depth. Each tilt meter consists of a 1-2 m deep, 500-m-long, 15-cm diameter, horizontal, half-filled water-pipe, terminated by float sensors with sub-micron water-level resolution, similar to those that have operated unattended for the past decade within the Long Valley caldera. The sensors measure water height relative to the base of a pile driven to 10 m depth. A wide-body LVDT attached to this pile outside the reservoir, senses the motion of the core attached to the float within. The voltage indicating the position of the core is sampled 16 times a second, and digitally filtered before transmission via radio modem for storage as 1-minute samples in a remote computer. The computer gathers 16-bit water height, vault temperature, air pressure and various housekeeping data once per minute using remote telemetry. Installed during 2004, the first of the tilt meters, installed in 2004, float sensors at each end, and one in the center of each pipe, permit us to examine tilt signal coherence and local noise. Each adjacent pair of sensors has a tilt resolution of 2e-9 and a range of 8 microradians. We anticipate tilt signals with durations of 0.3-30 days, and amplitudes of less than 0.1 microradian associated with slow earthquakes. Anticipated noise levels in the tilt meters are 10-1000 times lower that these expected signals, similar to or better than signal-to-noise levels from planned strain meters of the PBO array.
http://www.geodesy.cwu.edu
G51B-0090 0800h
Time Series Interferometry: Toward Weekly Observations
We present a method for using ScanSAR-SAR interferometry to obtain more frequent observations than is possible with current strip mode mapping. Envisat's repeat orbit time (35 days) and 5 ScanSAR sub-swaths can potentially generate weekly observations over very large areas, due to overlap between ScanSAR images. Our goal is to quantify slow deformation rates with a denser time series from a combination of Envisat's ASAR wide swath and image modes. We work on ScanSAR-SAR interferometry primarily because timing issues with the currently operating satellites prevent exploiting the full potential of direct ScanSAR-ScanSAR interferometry. However wide swath (ScanSAR) images have lower resolution than strip mode images, and eventual fringes have more speckle noise. For a resolution of 150 m, the speckle noise phase error can range from 0.65 rad to 1.4 rad, for terrain correlation values of 0.3 to 0.8 respectively. We simulate ScanSAR-SAR data processing with small "bursts" of ERS data (50 to 70 pulses) in accordance with Envisat's ScanSAR mode bursts, and process the bursts with a modified SPECAN algorithm [Lanari et al., 1998]. We find matching bursts by searching the strip mode image for a section whose Doppler frequency range matches the simulated ScanSAR burst Doppler frequencies. We evaluate the utility of the ScanSAR-SAR interferometry approach using the ERS data simulation. Depending on Envisat's data availability we will also present Envisat ScanSAR-SAR interferograms.
G51B-0091 0800h
Geological Features Extraction and Fusion Using Wavelet Transform of ASTER Images: Examples from the Neoproterozoic Allaqi-Heiani Suture, Southeastern Egypt
Redundant wavelet transform (RWT) and discrete wavelet transform (DWT) are applied to the Advanced Spaceborne Thermal Emission and Reflectance Radiometer (ASTER) data to trace along strike continuation of geological structures in the E-W trending Neoproterozoic Allaqi-Heiani Suture in southern Egypt. Geological structures in the Allaqi-Heiani Suture are in the form of S-verging fold and thrust belt that constitute three nappes defined by distinctive lithological units specially ophiolite components including talc schist, serpentinite, and gabbro. Ophiolite components are distinctive from the surrounding rock types and they can be separated on the basis of their spectral characteristic in ASTER data using the RWT and DWT. The separated structural and lithological information is further fused together while the spectral information of their surrounding rock types is suppressed. Our results indicate that the lower nappes in the suture can be traced for the entire length of the suture whereas the upper nappes are folded about N-S trending axis.