Showing papers by "Geophysical Survey published in 2010"

Data Analysis Techniques for GPR Used for Assessing Railroad Ballast in High Radio-Frequency Environment

Abstract: Railroad ballast supports heavy rail loading, prevents track deformation, and provides drainage of water from the track structure. However, over time, ballast is fouled by the breakdown of ballast aggregate and/or the infiltration of fines, which undermine the ballast functions and affect the railroad track structural capacity. Ground penetrating radar (GPR) provides a rapid, effective, and continuous way to assess railroad track substructure condition; especially ballast. However, the GPR system faces some challenges during field surveys including high radio-frequency interference from railroad communication and automation, and strong reflections from rails. In this study, appropriate techniques were used to remove the interference and reduce the strong clutter from rails to obtain clear GPR data of railroad substructure. A time-frequency method, short-time Fourier transform, was then applied to extract ballast fouling condition over depth. A field survey using multiple sets of 2-GHz air-horn antennae was conducted during summer 2007 at the Transportation Technology Center, Inc. in Pueblo, Colo. Compared to ground-truth excavation and ballast gradation analysis results, GPR was found to be an effective technique to assess railroad track ballast substructure condition.

Optimization of antenna configuration in multiple-frequency ground penetrating radar system for railroad substructure assessment

Abstract: This paper discusses the use of ground penetrating radar (GPR) to rapidly, effectively, and continuously assess railroad track substructure conditions, especially ballast. To overcome the limited electromagnetic waves penetration for high-frequency antennae and the low resolution of low-frequency antennae, this study uses a multiple-frequency GPR system to assess railroad substructure conditions. High-frequency antennae were used to detect the scattering pattern, which is related to air void volume in railroad ballast, and low-frequency antennae are used to assess deeper substructure conditions. Considering the scattering energy attenuation is highly frequency and material dependent, a time–frequency method based on tracking the frequency spectrum and energy change over depth can be used to extract ballast fouling conditions. From GPR field collected data, ground-truth observation, and ballast gradation analysis, the multiple-frequency GPR system demonstrates a promising capability to assess railroad track substructure condition.

Development of a time–frequency approach to quantify railroad ballast fouling condition using ultra-wide band ground-penetrating radar data

Abstract: This paper discusses the use of ground-penetrating radar (GPR) to assess railroad track substructure conditions. An ultra-wide band (UWB) GPR system, having a centre frequency at or higher than 2 GHz, can be used to detect the scattering pattern and to predict air void volume in railroad ballast. A time–frequency technique was implemented to characterise the signal in time and frequency domains simultaneously. Because electromagnetic energy attenuation is highly frequency dependent, the frequency sub-bands of the reflected UWB GPR signal can be analysed separately to quantify the fouling material and quantify moisture content. Additionally, to validate the GPR system capability, a ground truth field survey was conducted. Using ballast samples collected from the field for validation, this paper shows that a time–frequency analysis may provide a new method to measure the thickness of clean ballast, detect the trapped water and assess the ballast fouling and moisture content along the track.

CRInSAR for landslide deformation monitoring: A case in threegorge area

Abstract: Landslide in threegorge area is a severe geohazard threatening many people. Conventional differential SAR interferometry (DInSAR) and Persistent Scatterers for SAR interferometry (PSInSAR) technique are unsuitable for landslide deformation monitoring in this area due to temporal and lack of natural phase stable point targets. The method of DInSAR using corner reflectors (CRInSAR) is a powerful tool in the vegetation area. The procedure of DInSAR using corner reflectors (CRInSAR) used by this paper is briefly introduced. Using ENVISAT ASAR time series data, the deformation of 12 corner reflectors (CR) in Shuping landslide are analyzed. As to the CR with slow creep deformation, the CRInSAR results are reliable. But as to the CR with nonlinear accelerated deformation, our CRInSAR method still needs to be enhanced.

A method for InSAR baseline refinement and its application

Abstract: Interferometric baseline plays a very important role in InSAR data processing, and it will directly affect the accuracy of interferometric result. In this article, three classical baseline estimation methods were described. By comparing and combining three methods, a new baseline estimation method and its flow were listed. RADARSAT-2 satellite image data and grid digital elevation model ASTER GDEM (30m resolution) in Kailuan area are used as sample data. By analyzing the differential interferometric results generated with different baseline estimation methods, it can be concluded that the new method used by this article is correct and feasible.

Detection of land subsidence in Beijing, China, using Interferometric Point Target Analysis technique

Abstract: Land subsidence in Beijing is supposed to be caused by over-exploitation of ground water, which is leading to a rapid decline of water levels, drying out clay layers that finally result in land subsidence.

Specialized seismic noise registration station “Nachiki” in the geophysical monitoring system of Kamchatka

Abstract: The specialized station of high-frequency seismic noise registration “Nachiki” is described arranged on Kamchatka in 1987. The instrument-methodical aspects of registration are considered, as well as history of observations development. New principal experimental results of surveys are represented. The results of use of high-frequency seismic noises are summarized to reveal strong earthquake precursors in the online mode in 1996–2008.

Experimental approach for determining the received pattern of a Rascan holographic radar antenna

Abstract: Because of the nature of image formation for holographic radar, the role and relevance of antenna radiation pattern are different than for impulse radar, and thus have not been studied. We determine theoretical Rascan radiation patterns for different dielectric media, and compare simulations to experimental data from an antenna scanned across a spherical metal target at various ranges/depths. Positions at which the received signal (phase difference between object and reference beams) are the same within a single scan, and across scans at different depths provide a 3-D approximation of the effective radiation pattern that closely agrees with the simulations.

Application of Combined Spectra of Mixed Minerals to Mapping Altered Minerals:A Case Study in the Yunnan Region Based on Hyperion Data

Abstract: In nature,coexistence and combination of minerals have definite rules.Thus the combination and subdivision of altered minerals are more important than single ones in geological mapping and survey.Based on such rules and geological purposes,some minerals,that are not easy or necessary to distinguish,can be identified as one set of minerals.And they are calculated as an end member in decomposition of mixed spectra.This is another approach to solve mixed spectra of minerals.In this work we use the Hyperion spectral data in the Xiangelila area,Yunnan province to identify the mineral combination of limonite and sericite.Then we obtain and analyze the data of altered rocks in high-elevation areas of Yunnan and prepare maps of remote sensing alternation.And we conducted field investigations at the sites where alternation anomalies were extracted from the map.The identification result shows that the study area has mountains over 4000 m,little vegetation and many outcrops.Although the interferences are large,information extraction has attained satisfactory results.With help of other data,this method can be used to delineate prospective mineralization and target areas.

Seasonal Changes in Vibroseismic Monitoring Experiments in Siberia

Abstract: We present the results of a long-term experiment involving vibroseismic monitoring of the Earth’s crust, which began in 1997 in the Thom’-Kolyvan’ fold zone. Two vibrators of 100- and 40-ton force were used as excitation sources. One three-component (3C) sensor was placed 3 m under the source platform, while another 3C sensor was located at the Novosibirsk Seismological Station, 49 km from the vibrators. Data were collected periodically during several years. The seasonal variations in the frequency characteristic of the vibrator radiation have been investigated. Freezing and thawing of the ground was found to have an effect on vibrator radiation, such that there are distinct winter and summer radiation patterns generated by the vibrator (as well as transition periods in between). The seismograms from the remote zone also reveal cyclical changes in winter and summer. Travel-time wave attributes do not vary with freezing or thawing of the ground, while the dynamic behavior of recorded traces has a pronounced correspondence with freezing or thawing for different years. More detailed research has found that the freezing and thawing of the ground affect not only the radiation spectrum, but also the directional diagram of the source.

DInSAR for land subsidence monitoring using high resolution COSMO-SKYMED SAR Data: Preliminary results compared with ASAR

Abstract: DInSAR can map ground deformation phenomena over tens-of-kilometers-wide area with centimeter-scale accuracy level, and has been considered as a powerful tool. Because of the data availability, previous DInSAR applications were mainly base on ERS, JERS, ENVISAT ASAR, and RADARSAT-1 data with resolution coarser than 10m. Nowadays, several kinds of high resolution SAR data are available for DInSAR and there are high expectations for the application of these data. In this paper, COSMO-SkyMed SAR data and grid digital elevation model ASTER GDEM (30m resolution) are used as research data. COSMO-SkyMed SAR data are preliminary processed by DInSAR technique for land subsidence mapping of Tianjin and Beijing area. Meanwhile, the DInSAR results from COSMO-SkyMed and ASAR data are preliminary compared. COSMO images are more suitable to extract high-precision ground deformation information than ASAR images in civil application given precise orbit data. While COSMO data are suitable for deformation monitoring in a relatively small and important area, ASAR data are fit for regional survey.

A study on different PS-like methods for subsidence in Tianjin, China

Abstract: In this paper, the methods, primary PS-like method and Stanford Method for PS (StaMPS) are both studied and used to monitor the subsidence in Tianjin area.

The analysis on parameters of the payload on hyperspectral satellite

Abstract: This paper focuses on the analysis and selection of space-borne hyperspectral sensor parameters, through the simulation of the entire data acquisition process and the applications using simulated hyperspectral data. Aiming at the alteration mineral identification and mapping, we used the simulated space-borne hyperspectral data with different payload parameters including the spatial resolution, spectral resolution and Signal-to-Noise-Rate (SNR) from HyMAP air-borne hyperspectral data in Dongtianshan area in Xinjiang Province of China to identify and map the alteration minerals, so that we could analyze and compare these results to find the optimal combination of payload parameters. A combination of the parameters of 30m spatial resolution, 10 - 20nm spectral resolution and 200:1 (VNIR) / 150:1 (SWIR) SNR was evaluated to possess the strongest ability for the mineral identification and mapping. This technology can also be promoted by the other payload parameter analysis and selection.