G53B-0634
Hyperscale Morphological Models of Braided Rivers: Multi-scale retrievals with Terrestrial Laser Scanning
In the last decade, advances in topographic survey and digital elevation modelling have enabled a revolution in the study of river morphology and fluvial processes. Prior to the late 1990s, the analysis of channel form and dynamics was typically restricted to inferences from cross-sections and planform mapping. Since then, advances in survey instrumentation (e.g., Brasington et al., 2000) and remote sensing (Westaway et al., 2000; Brasington et al., 2003; Charlton et al., 2003) have enabled the collection of dense topographic data and the opportunity to build high-resolution, precision DEMs, ideally suited to morphometric analysis, sediment budgeting and as boundary models for fluid simulations. Continuing developments in survey technology are now poised to reset the parameters of this field once again through the recent emergence of ruggedized, terrestrial laser scanners. Based on time-of-flight or phase-based laser ranging, these instruments are capable of acquiring unprecedented volumes of survey-grade observations at operating frequencies of between 5-500 kHz and over ranges 25-1000 m. This new technology offers the potential to acquire rapidly, reach-scale datasets which record topographic information at the resolution of bed grain-scale upwards. This hitherto unprecedented data-stream presents new opportunities for river science, but also creates significant challenges particularly associated with: data management; regularization of resolution; visualization; and data assimilation with parallel models and data- products. In this paper we present a new methodology designed to analyze large 3d point clouds generated by terrestrial laser scanning. Specifically, the approach generates multi-resolution gridded terrain products from scan data whilst retaining the sub-grid scale information as key statistical attributes. We apply the method to a 1 km reach of the River Feshie, Scotland which was scanned in 2007 and evaluate the results through a comparison with independently acquired, spatially dense, GPS surveys of the study reach. The results reveal significant differences in the topographic signatures recorded by the two methods and reveal the value of the enhanced spatial resolution for representing complex morphologies and highlight the potential to retrieve grain-scale sorting patterns from the statistical attributes of the TLS data. Keywords: Terrestrial Laser Scanning, DEM, multi-resolution models, grain-scale, reach-scale, River Feshie
G53B-0635
Terrestrial Laser Scanning Study of Gully Erosion at West Bijou Creek, Arapahoe County, Colorado: An Investigation on Field Acquisition and Data Processing
Terrestrial laser scanning (TLS) or ground based LiDAR (light detection and ranging) is a relatively new technology that digitally maps geological outcrops at a (mm-cm) resolution. This paper reports the results of a trial TLS project that has two main aims: collecting scans for monitoring gully erosion and conducting a survey to connect field methods of TLS with geomorphology. The site of the TLS survey was located at Arapahoe County, Colorado and data collection consisted of a three-day campaign. This project focus is applying a new approach to analyzing and measuring deformation and erosion in gully dominated landscapes. Our approach to make the survey consisted of going to the field with an Optech scanner to acquire the data, searching for different field acquisition strategies, practicing with data processing and making a web page of the project for the scientific community. A preliminary terrain model is made in Polyworks software using only twenty percent of the scans and giving us an insight of how the landscape model can look in the future. The long-term goal of this research is to keep track of the changes in the morphology of the gullies located at the West Bijou Creek in Colorado using Real Time Kinematic GPS (RTK- GPS) and Terrestrial Laser Scanning (TLS). Because applications of TLS in geology and geophysics are evolving rapidly, in this project a web page including a forum is made to provide the scientific community with a summary of current field acquisition practices for sharing ideas and discoveries.
G53B-0636
Extraction of Features from High-resolution 3D LiDaR Point-cloud Data
Airborne and tripod-based LiDaR scans are capable of producing new insight into geologic features by
providing high-quality 3D measurements of the landscape. High-resolution LiDaR is a promising method for
studying slip on faults, erosion, and other landscape-altering processes. LiDaR scans can produce up to
several billion individual point returns associated with the reflection of a laser from natural and engineered
surfaces; these point clouds are typically used to derive a high-resolution digital elevation model (DEM).
Currently, there exist only few methods that can support the analysis of the data at full resolution and in the
natural 3D perspective in which it was collected by working directly with the points. We are developing new
algorithms for extracting features from LiDaR scans, and present method for determining the local curvature
of a LiDaR data set, working directly with the
individual point returns of a scan. Computing the curvature enables us to rapidly and automatically identify
key features such as ridge-lines, stream beds, and edges of terraces. We fit polynomial surface patches via
a moving least squares (MLS) approach to local point neighborhoods, determining curvature values for each
point. The size of the local point neighborhood is defined by a user. Since both terrestrial and airborne LiDaR
scans suffer from high noise, we apply additional pre- and post-processing smoothing steps to eliminate
unwanted features. LiDaR data also captures objects like buildings and trees complicating greatly the task of
extracting reliable curvature values. Hence, we use a stochastic approach to determine whether a point can
be reliably used to estimate curvature or not. Additionally, we have developed a graph-based approach to
establish connectivities among points that correspond to regions of high curvature. The result is an explicit
description of ridge-lines, for example. We have applied our method to the raw point cloud data collected as
part of the GeoEarthScope B-4 project on a section of the San Andreas Fault (Segment SA09). This section
provides an excellent test site for our method as it exposes the fault clearly, contains few extraneous
structures, and exhibits multiple dry stream-beds
that have been off-set by motion on the fault.
http://www.keckcaves.org
G53B-0637
Rockfall Measurements in Alpine Catchments by Using Terrestrial Laserscanning
The main goals of the investigation are to quantify rockfall from rock faces and to improve rockfall models. Up to now quantification of rockfall was done by indirect measurements on the rockfan, for example by nets. These methods were error-prone and did not consider for example lithological differences on the rock faces. So a differentiation between primary (weathering) and secondary rock fall (fluvial erosion) was not possible. So without this dif-ferntiation an exact quantification of erosion by weathering on rock faces is not feasible. In the presented research project a high resolution Terrestrial Laserscanner (Riegl LMS Z420ii) is used to quantify weathering on rock faces by multitemporal measurements (twice to thrize a year). Aditionally the rockfans are scanned too. So the runout distance of rocks can be determined. These measurements are done in three alpine catchments, which are situated in the northern (Wettersteinmountains near Garmisch Partenkirchen, Germany), the central (Oetztal, Austria) and the southern part (Villnoesstal, Italy) of the alps. The three catchments have different climatic and lithologic conditions (Limestone, gneiss, dolomite). Beside the quantification of rockfall activity the measurements can help to develop rockfall models and to improve existing rockfall models. With the high reolution spatiotemporal data the disposition for rockfall activity can be modelled and so active areas on a rock face can be differentiate from inactive areas. By knowing the starting areas of rock fall and knowing the runout distances of rocks on rock fans, existing process models which predict runout distances, can be improved. The submitted poster presentation should show first analyses and results of the project which started in fall 2007.
G53B-0638
Velocity Field Estimation Using Terrestrial LiDAR 3D Point Cloud Data
Three dimensional point cloud data from Terrestrial Laser Scanners (TLS) has the capability of monitoring ground displacements. In particular, TLS is better suited than InSAR to estimate ground displacement of small spatial extent (eg. Landslides). Problems arise, however, when characterizing the velocity field from the TLS data set as a unique position of points in the point cloud time series is undefined. In this study, a technique is presented to calculate the velocity field using temporal point cloud data acquired from ILRIS 3D TLS. A two-dimensional grid surface is generated with pixel value representing the third dimensional value taken as the target range from the TLS unit. The interpolated 2D image then contains 3D spatial position. A gradient based motion estimation technique then is applied to constrain the velocity field at each image pixel. Finally, the motion constraints are convolved with a Gaussian window function in order to calculate a smooth velocity field. This technique is applied to synthetic data, the TLS data from a controlled experiment and data from active Pu'u Oo volcanic vent. Synthetic data and controlled experimental data were used to demonstrate that the accuracy of the technique is of the order of centimeters. In addition, the implementation of the technique to characterize ground motion associated with other geological processes such as a landslide and some practical considerations of the technique are presented.
G53B-0639
Kinematic GPS Profiles to monitor surface deformation
GPS kinematic measurement consists in placing a GPS rover receiver that registers its position on a moving
vehicule with a high frequency. The frequency of the data acquisition is chosen according to the number of
points and the precision needed to characterize the rover trajectory. The position of the rover receiver can
be determined with respect to another GPS reference station with a precision of a few centimeters.
Consequently different kinematic profiles on trajectories can be realized in different contexts (volcano slopes,
active faults,...).
We first studied the correlation between different profiles on the same trajectory in the absense of any
particular event. Then different individual profiles are interpolated and a single profiles is generated which we
refer to as "tube". We also studied and analyzed the impact of different parameters such as the baseline
length, the atmospheric errors and the number of individual profiles on the precision of the obtained tube.
We present results of experimentations that were performed in Chili, Reunion Island and Greece and we
show how the results can be influenced by the baselines lengths and topographies.
In case of event (Earthquakes, volcanoes eruptions, landslides,...) this technique can be used to assess the
amplitude of ground deformation. We estimate the thresholds (in term of amplitude and spatial extension) of
detectable signals.
G53B-0640
Hydrology-Induced Tilt Deformation: a case Study on a Karst System on the Larzac Plateau (France)
The aim of this study is to bring new information on water storage dynamics on karst systems from tiltmeter measurements. Newly developped long base tiltmeters are installed at two sites on the Larzac plateau (France) in a karst aquifer of ~100 km2 recharge area. Each site is located below the surface within a karstic cave where two tilt directions are monitored with a 2 mn sampling rate. The first site, installed in July 2006 at 50 m depth at the center of the aquifer, consists of 11 m and 23 m baselines of respectively N011° and N094° directions. The second site is installed in June 2007 at 15m depth and monitors the N111° and N326° directions with respectivelly 4.5 and 9 m baselines. It is located in the South of the recharge area, furthest away from the outlet. Significant reversible tilt deformation is observed at both sites consecutive to each heavy rain ( more than 100 mm of water). The reversible tilt signal reaches amplitudes of 10-6 and 10-5 radians and has 20 days and 100 days time constant for respectivelly the deep and shallow site. The maximum tilt signal has a fixed direction regardless of the rainfall event. Because ground-based gravity studies have recently demonstrated that most water storage variations occur in the shallow part of the aquifer, we attempt to link tilt deformation at both sites to water storage variations in the uppermost weathered zone known as epikarst. Mechanisms responsible for the observed tilt can be the following: differential water storage repartition leading to differential elastic loading or water pressure induced fracture deformation. In order to discriminate between these two mechanisms, an experiment in which the shallowest tiltmeter site was loaded at its surface by up to 25 tons of weight (using tractors) at strategic locations was conducted. An elastic halfspace model accounts for all but one of the observed tilts, and elastic parameters for the medium are determined. We argue that pressure effect in fractures seem to be the dominant mechanism responsible for observed deformation for at least one of the studied site.
G53B-0641
4D Absolute Gravity, Surface to Depth Gravity and Microgravity Measurements: Application to Groundwater Monitoring in a Karst System in the Larzac Plateau (France)
In this study we attempt to understand the water storage variations in a karst aquifer on the Larzac Plateau (South of France) using ground-based gravimetry. Surface to 60 m depth gravity measurements are performed three times a year since 2006 down a pothole, in complement to monthly absolute gravity (AG) measurements at three sites. Absolute gravity variations are explained with a mass balance model taking into account precipitation, evapotranspiration and spring discharge. Preferential water storage is observed at the south AG site, in agreement with geomorphological interpretation of that area. The time variations of the surface to depth gravity differences are compared to the absolute gravity variations. Using a simple Bouguer plate model, we find that surface to depth (STD) gravity differences are very similar to absolute gravity variations. We argue that AG and STD differences monitor water storage variations in the uppermost zone of the karst known as epikarst. We discuss the geological and hydrological reasons for such a dominant water storage variation of the epikarst. To complement AG and STD measurements, microgravity surveys including 40 stations covering the karst recharge area are performed twice a year during wet and dry seasons. The comparison of the gravity field obtained for each survey period delineates areas of high and low water storage on the recharge area. The average gravity value on the recharge area for each survey period compares favorably to the mass balance model. The joint use of time-lapse AG, microgravity surveying and surface to depth gravity measurements is an efficient method to quantify groundwater storage variation in space and in time in karst areas where classical hydrological methods have severe limitations.
G53B-0642
A study on the relationship between tropospheric delay and GPS post-kinematic positioning
The positioning accuracy of the Global Positioning System (GPS) has been studied extensively and used widely. It is still limited due to errors from sources such as the ionospheric effect, orbital uncertainty, antenna phase center variation, signal multipath and tropospheric disturbance. For GPS static and kinematic positioning, its accuracy has been significantly improved over the past few years with the advanced technology. Since the typical practice of GPS positioning ignores the natural inhomogeneity of atmospheric water vapor, high precision positioning is limited, especially in its vertical component. The first step to reduce, if not eliminate, the influence of the presence of tropospheric delay shall be understood and modeled. This investigation addresses the tropospheric effect on the GPS post-kinematic positioning determination. The impact will be examined quantitatively using data acquired from permanent GPS stations along with meteorological measurements. Computations based on independent baseline as well as networking will be simultaneously investigated and analyzed. It is expected the accuracy of GPS post-kinematic positioning determination will be increased especially in the vertical component.
G53B-0643
Lake Chabot GPS deformation network. From tectonic deformation monitoring to calibration network.
The Lake Chabot is located less than 5 km east of the Hayward Fault and might constitute a network able to constrain the slip distribution along the southern Segment of the Hayward Fault during the next seismic event. Additionally, this network will be able to document the displacement in near-field during the next large magnitude rupture. This network is composed of ten monuments located around the lake. This network allows us to survey the deformation of the ground around the lake using multiple techniques (GPS, Total station, LASER, etc.). This innovative concept will allow the GPS user, in collaboration with EBMUD, EBRPD and UCB to test and calibrate their instruments periodically, enabling new field techniques (RTK using PBO sites) as well as updating its processing capabilities with other users using a realistic network (multipath, masks, etc.). We present here displacement field inferred from synthetic models and rupture models expected in order to test the sensitivity of this small scale GPS network. As various activities are completed on a daily basis by participating institution in this area, this displacement field is over layered by various information already available and relevant to the deformation of the area.
G53B-0644
The final year of GPS Installations in the Alaska Region of the Plate Boundary Observatory
The Plate Boundary Observatory (PBO) is the geodetic component of the National Science Foundation funded Earthscope Project. The final PBO GPS network will comprise 1100 continuously operating GPS stations installed throughout the Western US and Alaska. The Alaska region is an important area of study because of the major crustal deformation and high volcanic activity associated with the subduction of the Pacific Plate beneath the North American Plate. The PBO network will provide data to help better understand these earth processes. In the fifth and final year of the PBO installation phase, we built 31 GPS Stations and installed 8 tilt meters in Alaska. These installs completed the PBO network in Alaska which comprises 135 GPS stations and 12 tilt meters. We also completed maintenance visits to GPS stations installed during earlier years of the five year project. In the 2008 field season we faced some of our most difficult logistical challenges with installations in remote areas, islands and volcanoes. Highlights include boat-based helicopter supported installs in the Shumagin Islands on Chernabura, Nagai and Popof; and 13 GPS stations and 8 tiltmeters installed on Unimak Island to monitor Westdahl and Shishaldin volcanoes. The Unimak installations were completed in a four week period and were carried out in cooperation with scientists from the Alaska Volcano Observatory. We also installed the remaining stations monitoring the Denali fault and integrated the Denali earthquake response stations built by University of Alaska Fairbanks into the PBO network. Now that the installations are completed, the PBO network will be operated and maintained by UNAVCO engineers for the next 10 years. Data from all of the PBO stations are available from the UNAVCO archive.
G53B-0645
GPS Installation Progress in the Northern California Region of the Plate Boundary Observatory
The Plate Boundary Observatory (PBO) is the geodetic component of the National Science Foundation (NSF) funded Earthscope Project. The final PBO GPS network will comprise 1100 continuously operating GPS stations installed throughout the Western US and Alaska. There are 448 Stations planned for California with 231 of these in Northern California (NCA). This poster will present a progress report and highlights of GPS installations in NCA over the past year up until the end of the five year project. In the fifth year of the project (beginning 10/1/2007 and ending 10/1/2008), we installed 40 additional stations for a total of 231 stations. The stations installed include; 8 station installed at Lassen Volcanic National Park, 2 additional stations built around Mount Shasta (8 total), 3 stations built in Yosemite National Park, 2 in the Mendocino National Forest, and 2 stations in Tahoe National Forest. The higher elevations stations required modification for use in areas of high snow load and high wind. Data from these stations are available from the UNAVCO archive. In addition to the installations, there was a gradual shift of resources from installation to the operation and maintenance aspects of the growing GPS network. Telemetry priorities moved from individual stations telemetry solutions to grouped telemetry solutions to increase efficiency and reduce costs.
G53B-0646
Support of EarthScope GPS Campaigns at the UNAVCO Facility
In order to support portable GPS deployments funded by the NSF's EarthScope Science panel, PBO has purchased 100 campaign GPS systems. Based Topcon GB-1000 equipment, the systems have been designed for stand-alone temporary or semi-permanent deployment that will be used for densifying areas not sufficiently covered by continuous GPS, and responding to volcanic and tectonic crises. UNAVCO provides support for all aspects of these projects, including proposal and budget development, project planning, equipment design, field support, and data archiving. Ten of the 100 systems have been equipped with real-time kinematic (RTK) capability requiring additional radio and data logging equipment. RTK systems can be used to rapidly map fault traces and profile fault escarpments and collect precise position information for GIS based geologic mapping. Each portable self-contained campaign systems include 18 Ah batteries, a regulated 32 watt solar charging system, and a low-power dual frequency GPS receiver and antenna in a waterproof case with security enhancements. The receivers have redundant memory sufficient for storing over a year's worth of data as well as IP and serial communications capabilities for longer-term deployments. Monumentation options are determined on a project-by-project basis, with options including Tech2000 masts, low-profile spike mounts, and traditional tripods and optical tribrachs. Drilled-braced monuments or masts can be installed for "semi- permanent" style occupations. The systems have been used to support several projects to date, including the University of Washington's 30-unit deployment to monitor the Episodic Tremor and Slip event in November, 2005 and the ongoing Rio Grande Rift experiment, run by the Universities of Colorado, Utah State, and New Mexico, which has seen the construction of 25 permanent monuments in 2006 and 2007 and a 26-site campaign reoccupation in 2008.