• 한국지구물리탐사학회:학술대회논문집
• /
• 2007.12a
• /
• pp.31-42
• /
• 2007

Dc resistivity monitoring has been increasingly used in order to understand the changes of subsurface conditions in terms of conductivity. The commonly adopted interpretation approach which separately inverts time-lapse data may generate inversion artifacts due to measurement error. Eventually the contaminated error amplifies the artifacts when reconstructing the difference images to quantitatively estimate the change of ground condition. In order to alleviate the problems, we defined the subsurface structure as four dimensional (4-D) space-time model and developed 4-D inversion algorithm which can calculate the reasonable subsurface structure continuously changing in time even when the material properties change during data measurements. In this paper, we discussed two case histories of resistivity monitoring to study the ground condition change when the properties of the subsurface material were artificially altered by injecting conductive materials into the ground: (1) dye tracer experiment to study the applicability of electrical resistivity tomography to monitoring of water movement in soil profile and (2) the evaluation of cement grouting performed to reinforce the ground. Through these two case histories, we demonstrated that the 4-D resistivity imaging technique is very powerful to precisely delineate the change of ground condition. Particularly owing to the 4-D inversion algorithm, we were able to reconstruct the history of the change of subsurface material property.

• Geomechanics and Engineering
• /
• v.35 no.2
• /
• pp.109-119
• /
• 2023

Ground subsidence in urban areas due to excessive development and degraded underground facilities is a serious problem. Geophysical surveys have been conducted to estimate the distribution and scale of cavities and subsidence. In this study, electrical resistivity tomography (ERT) was performed near an area of road subsidence in an urban area. The subsidence arose due to groundwater leakage that carried soil into a neighboring excavation site. The ERT survey line was located between the main subsidence area and an excavation site. Because ERT data are affected by rapid topographic changes and surrounding structures, the influence of the excavation site on the data was analyzed through field-scale numerical modeling. The effect of an excavation should be considered when interpreting ERT data because it can lead to wrong anomalous results. A method for performing 2D inversion after correcting resistivity data for the effect of the excavation site was proposed. This method was initially tested using a field-scale numerical model that included the excavation site and subsurface anomaly, which was a loosened zone, and was then applied to field data. In addition, ERT data were interpreted using an existing in-house 3D algorithm, which considered the effect of excavation sites. The inversion results demonstrated that conductive anomalies in the loosened zone were greater compared to the inversion that did not consider the effects of excavation.

• Proceedings of the KSRS Conference
• /
• 2008.10a
• /
• pp.33-36
• /
• 2008

This paper presents soil moisture retrieval from measured polarimetric backscattering coefficients of a vegetated surface. Based on the analysis of the quite complicate first-order radiative transfer scattering model for vegetated surfaces, a simplified scattering model is proposed for an inversion algorithm. Extraction of the surface-scatter component from the total scattering of a vegetation canopy is addressed using the simplified model, and also using the three-component decomposition technique. The backscattering coefficients are measured with a polarimetric L-band scatterometer during two months. At the same time, the biomasses, leaf moisture contents, and soil moisture contents are also measured. Then the measurement data are used to estimate the model parameters for vv-, hh-, and vh-polarizations. The scattering model for tall-grass-covered surfaces is inverted to retrieve the soil moisture content from the measurements using a genetic algorithm. The retrieved soil moisture contents agree quite well with the in-situ measured soil moisture data.

• Clean Technology
• /
• v.6 no.1
• /
• pp.51-60
• /
• 2000

The soil remediation by non-ionic surfactant solutions ($C_{12}H_{25}O(CH_2CH_2O)_5H$ and Triton X-100) was studied. Depending on the amounts and use of co-surfactants, MPT(phase inversion temperature), dynamic interfacial tension, and the detergency efficiency of the surfactant solutions in soil were investigated. The oils used were kerosene, n-hexadecane, and paraffin oil. With respect to a higher detergency efficiency, a lower interfacial tension and the MPT was very important. The $C_{12}H_{25}O(CH_2CH_2O)_5H$ was better than Triton X-100 on the oil removal from the soil and the effect of oil kinds was kerosene>paraffin $oil{\geq}n-hexadecane$. The co-surfactant, n-dodecanol, reduced the MPT compared to no addition of this, whereas it did not enhance the detergent efficiency.

• Journal of Korean Society of Forest Science
• /
• v.104 no.1
• /
• pp.43-49
• /
• 2015

The production of high quality seedlings is a very important phase in silvicultural systems for successful reforestation or restoration. The purpose of this study was to quantitatively measure both growth performances and nutrient responses of Fraxinus rhynchophylla, Pinus densiflora, and Pinus koraiensis seedlings, which are commercially planted in Korea, according to the different types of soil improvement treatments. We applied soil brought (hereafter 'brought'), subsoil inversion (hereafter 'subsoil'), and mixture of brought soil with soil on nursery bed (hereafter 'mixing') in a permanent national nursery. Silt and clay contents were the highest at the subsoil treatment and organic material, soil nitrogen and phosphorus concentrations were the lowest at the brought treatment. The growth of F. rhynchophylla was the lowest at the subsoil treatment, but there were no significant differences among treatments. There were significant differences in only root nutrient concentrations of F. rhynchophylla among treatments: nitrogen, phosphorus, and potassium concentrations were the lowest at the subsoil or brought treatment. Mixing treatment increased N contents with deduction of N concentrations ('dilution') because of more dry weight increase compared with the amount of N uptake. This study suggested mix of brought soil with soil on a nursery bed in a permanently used nursery can economically be an effective technique to improve soil quality.

• Proceedings of the KSRS Conference
• /
• 2005.10a
• /
• pp.737-740
• /
• 2005

Soil moisture, through its dominance in the exchange of energy and moisture between the land and atmosphere, plays a crucial role in influencing atmospheric circulation. To identify the crucial role, it is a common agreement that knowledge of land surface processes and development of remote sensing techniques are of great important scientific issues. This research uses TRMM satellite C band (10.65 GHz) data to retrieve soil moisture on the Tibetan Plateau in Mainland China. Two retrieval schemes that are implemented include the t-(J) model and the R model. The latter one is developed based on a land surface process and radiobrightness (R) model for bare soil and vegetated terrain. Compared with the in situ ground measurements, the soil moisture retrieved from the R model and the t-(J) model with vegetation information obviously appear more accurate than that derived from bare soil model. Retrieved soil moisture contents from the two inversion models, R model and t-(J) model, have a similar trend, but the former appears to be superior in terms of correlation coefficient and bias compared with in situ data. In the future, we will apply the R model with the TRMM 10.65 GHz brightness temperature to monitor long-term soil moisture variation over Tibet Plateau.

• Geophysics and Geophysical Exploration
• /
• v.8 no.1
• /
• pp.26-33
• /
• 2005

Inversion of multi-mode surface-wave phase velocity for shallow engineering site investigation has received much attention in recent years. A sensitivity analysis and inversion of both synthetic and field data demonstrates the greater effectiveness of this method over employing the fundamental mode alone. Perturbation of thickness and shear-wave velocity parameters in multi-modal Rayleigh wave phase velocities revealed that the sensitivities of higher modes: (a) concentrate in different frequency bands, and (b) are greater than the fundamental mode for deeper parameters. These observations suggest that multi-mode phase velocity inversion can provide better parameter discrimination and imaging of deep structure, especially with a velocity reversal, than can inversion of fundamental mode data alone. An inversion of the theoretical phase velocities in a model with a low velocity layer at 20 m depth can only image the soft layer when the first higher mode is incorporated. This is especially important when the lowest measurable frequency is only 6 Hz. Field tests were conducted at sites surveyed by borehole and PS logging. At the first site, an array microtremor survey, often used for deep geological surveying in Japan, was used to survey the soil down to 35 m depth. At the second site, linear multichannel spreads with a sledgehammer source were recorded, for an investigation down to 12 m depth. The f-k power spectrum method was applied for dispersion analysis, and velocities up to the second higher mode were observed in each test. The multi-mode inversion results agree well with PS logs, but models estimated from the fundamental mode alone show f large underestimation of the depth to shallow soft layers below artificial fill.

• Proceedings of the KSRS Conference
• /
• 2007.10a
• /
• pp.468-470
• /
• 2007

This paper is to present an approach for generating coarse resolution (MODIS data) fraction images of forested region in Korea peninsula using forest type area fraction derived from high resolution data (ASTER data) in regional forest area. A 15-m spatial resolution multi-spectral ASTER image was acquired under clear sky conditions on September 22, 2003 over the forested area near Seoul, Korea and was used to select each end-member that represent a pure reflectance of component of forest such as different forest, bare soil and water. The area fraction of selected each end-member and a 500-m spatial resolution MODIS reflectance product covering study area was applied to a linear mixture inversion model for calculating the fraction image of forest component across the South Korea. We found that the area fraction values of each end-member observed from high resolution image data could be used to separate forest cover in low resolution image data.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.17 no.8
• /
• pp.536-543
• /
• 2016

The installation of grounding systems is important for the safe operation of power systems, and the soil resistivity is an important design consideration for such systems. It varies markedly with the soil type, moisture content and temperature. The Jeju geological structure is formed in a multi-layered structure characteristic of volcanic areas and, and the geological ground resistance values can appear even constructed the same areas ground system different from the soil structure. In this study, a mock-up system using representative soil from Jeju was constructed to analyze the variation of the grounding resistance. The mock-up system was configured using the Gauss-Newton algorithm inversion method to analyze the model numerically using the Wenner method through the soil resistivity measurements used to create the ground model. Also, we analyzed the change in the general ground resistance characteristics of the copper rod, copper pipe, and carbon rod that are used for grounding. The variation of the grounding resistance with the hydration status was found to be $2.9[{\Omega}]$, $16.5[{\Omega}]$ and $20.1[{\Omega}]$ for the copper rod, copper pipes, and carbon rod, respectively, and the influence of the ground moisture resistance of the carbon rod was found to be the lowest with a value of $141[{\Omega}]$.

• Geophysics and Geophysical Exploration
• /
• v.6 no.4
• /
• pp.207-214
• /
• 2003

To analyze soil properties with depth in rice field, we compared resistivity distributions obtained from soil analysis with one dimensional inversion of small loop electromagnetic (EM) data. Although it didn't show consistency exactly between the two resistivity distributions, low resistivity zones in soil analysis, appeared to agree with low resistivity zones in EM result. Therefore, small loop EM method can be applied to obtain rapidly the soil properties such as salt accumulation in a rice field. If research on soil property and EM responses of unsaturated zone would be conducted consistently, small loop EM method can be used effectively to detect salt accumulated zone in agricultural area.