• Geophysics and Geophysical Exploration
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• v.25 no.1
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• pp.14-25
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• 2022

The passive surface wave method measures seismic signals from ambient noises or vibrations of natural phenomena without using an artificial source. Since passive sources are usually in lower frequencies than artificial ones being able to ensure the information on deeper geological structures, the passive surface wave method can investigate deeper geological structures. In the passive method, frequency dispersion curves are obtained after data acquisition, and the dispersion curves are analyzed by assuming 1D-layered earth, which is like the method of active surface wave survey. However, when computing dispersion curves, the passive method first obtains and analyzes coherence curves of received signals from a set of receivers based on spatial autocorrelation. In this review, we explain how passive surface wave methods measure signals, and make data processing and interpretation, before analyzing field application cases.

• Geophysics and Geophysical Exploration
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• v.17 no.4
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• pp.187-201
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• 2014

Compared with the separated inversion of electromagnetic (EM) and seismic data, a joint inversion using both EM and seismic data reduces the uncertainty and gives the opportunity to use the advantage of each data. Seismic fullwaveform inversion allows velocity information with high resolution in complicated subsurface. However, it is an indirect survey which finds the structure containing oil and gas. On the other hand, marine controlled-source EM (mCSEM) inversion can directly indicate the oil and gas using different EM properties of hydrocarbon with marine sediments and cap rocks whereas it has poor resolution than seismic method. In this paper, we have developed a joint EM inversion algorithm using a cross-gradient technique. P-wave velocity structure obtained by full-waveform inversion using plane wave encoding is used as structure constraints to calculate the cross-gradient term in the joint inversion. When the jointinversion algorithm is applied to the synthetic data which are simulated for subsea reservoir exploration, images have been significantly improved over those obtained from separate EM inversion. The results indicate that the developed joint inversion scheme can be applied for detecting reservoir and calculating the accurate oil and gas reserves.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.05a
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• pp.281-286
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• 2005

This paper presents sensitivity analysis of generalized rapid relaxation inversion (GRRI) algorithm for inverting controlled-source audio-frequency magnetotelluric (CSAMT) data. The algorithm was originally developed by modifying the RRI algorithm to recover a two-dimensional (2-D) conductivity structure of the Earth from MT data, but can be extended to include CSAMT data if it is combined with 2.5-D forward modeling. These GRRI approximate sensitivities are validated by comparison with exact 1-D and 2.5-D sensitivities. The comparison shows that the GRRI sensitivity is a good approximation to the exact sensitivity and has about half magnitude of the RRI sensitivity. Although the magnitude of the GRRI sensitivity is still slightly larger than that of the 2.5-D sensitivity, both sensitivities are broadly similar in shape when source-receiver offsets are greater than one skin depth on the Earth.

• Geophysics and Geophysical Exploration
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• v.3 no.3
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• pp.83-87
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• 2000

The noise prediction filter using a local/remote reference was developed to obtain a high quality data from seismic surveys over the area where seismic transmission power is limited. The method used in the noise prediction filter is a 3-layer neural network whose algorithm is backpropagation. A NRF (Noise Reduction Factor) value of about 3.0 was obtained with appling training and test data to the trained noise prediction filter. However, the scaling technique generally used for minimizing EM noise from electric and electromagnetic data cannot reduce seismic noise, since the technique can allow only amplitude difference between two time series measured at the primary and reference sites.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.310-310
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• 2023

기상레이더는 강우의 공간분포를 관측하고 강우장 이동특성을 예측하여 집중호우, 태풍 등에 대비할 수 있는 시간을 확보하기 위하여 운용되고 있다. 기상레이더는 전파를 송신하고 대기 중의물체(수상체, 건물 등)에 부딪혀 되돌아오는 신호를 수신하여 강우의 양, 분포, 이동방향 등을 산정할 수 있으며 세부적으로 입체관측(volume scan)을 반복하여 고도각 별로 거리와 방위각에 따라 다양한 합성영상을 산출할 수 있는 특성이 있다. 본 연구는 구름의 수평적 분포를 파악하는데 용이하여 기존에 널리 사용된 CAPPI 합성영상과 최근 현업에서 복잡한 지형으로 인한 오차를 해소하고자 광범위하게 사용되고 있는 다중 고도각 기반 레이더 강수량(hybrid surface rainfall, HSR) 합성영상을 취득하여 수문해석을 위한 유역단위 면적강수량의 추정오차를 검토하였다. HSR 합성영상은 우리나라와 같이 산악지형이 많이 존재하는 경우 지형의 영향을 받지 않아 지면에 가장 가까운 고도각의 관측자료를 사용하므로 지상관측소 강수량과 비교한 결과에서 기존의 CAPPI 합성영상 레이더 강수량과 통계적 효율 기준을 산정하여 레이더 강수의 품질이 개선되는 것을 확인하였다. 최근 환경부에서 추진하고 있는 인공지능(AI) 홍수예보 및 가상모형(Digital Twin)을 활용하여 홍수정보를 생산 및 전달하는 과정에서 유역의 지형적 특성을 현실적으로 고려한 레이더 강수량을 사용함으로 기후변화에 따라 국지적으로 발생하는 집중호우 대응 및 과학적 홍수관리를 실현할 수 있을 것으로 판단된다.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.06a
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• pp.279-284
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• 2007

The cultural noise sources in magnetotellurics were localized using the source localization method. Conventional beamforming techniques are not applicable for electromagnetic source localization. In this study, the matched field processing and genetic algorithm are used to localize an electromagnetic source and estimate the polarization direction. The source localization using MT field data shows the characteristics of estimated source distribution related to the strength of cultural noise.

• Proceedings of the Korea Information Processing Society Conference
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• 2022.11a
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• pp.344-346
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• 2022

본 논문에서 거푸집의 가장취약 부분인 접합부위에 로드센서를 부착하여 실시간 콘크리트 측압을 측정 할 수 있으며, 관리자는 모니터링을 통하여 확인 할 수 있도록 하며 LORA의 저전력 장거리 통신망을 사용하는 디바이스를 개발하여 로드센서에 측정한 값을 데이터변경, 웹 기반의 클라우드 서비스로 발송하여 PC 및 Mobile로 확인 할 수 있는 시스템을 구축하였다. 여러가지 센서로부터 데이터를 수신하여 모바일로 송신해 주는 무선송수신기의 개발을 원하고 있으며, 하중센서, 경사도센서, 풍향센서 등 다중 데이터값을 수신할 수 있어야 한다. 이렇게 구성된 센서와 데이터의 수신을 통해서 콘크리트 타설시 발생하는 측압을 측정하고 공사기간 동안 별도의 전원 공급 없이 작동이 유지될 수 있는 시스템을 구축하였다. 수요자가 Application과 호환이 이루어져야 하며 또한 MEMS센서를 이용하여 상태를 모니터링 하고 임계값을 지정하여 이상 신호 발생시 위험상황에 대해서 인공지능기법을 이용하여 관리자에게 알림을 주어 효과적으로 사용할 수 있는 시스템을 개발하였다.

• Journal of Advanced Navigation Technology
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• v.28 no.2
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• pp.193-200
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• 2024

This paper describes the design and development of a transmit receiver module(TRM) for mounting on X-band SAR of the NEXTSat-2. The TRM generates the chirp signal with required bandwidth through the DDS in X-band and performs frequency conversion, combination for the signal to transmit and be received and frequency synthesis. Tx path of the TRM produces signals of total 28 bandwidths up to 96.8 MHz and has output signal level of more than + 9.37 dBm. Rx path of the TRM has minimum noise figure of 15.7 dB. The measurement results show that required requirements are satisfied. The TRM is installed on the NEXTSat-2 flight model(FM), launched by KSLV-II(Nuri) on May 23, 2023 and currently operational.

• Geophysics and Geophysical Exploration
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• v.17 no.3
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• pp.163-170
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• 2014

Development of a modeling technique for accurately interpreting electromagnetic (EM) data is increasingly required. We introduce finite difference (FD) and finite-element (FE) methods for three-dimensional (3D) frequency-domain EM modeling. In the controlled-source EM methods, formulating the governing equations into a secondary electric field enables us to avoid a singularity problem at the source point. The secondary electric field is discretized using the FD or FE methods for the model region. We represent iterative and direct methods to solve the system of equations resulting from the FD or FE schemes. By applying the static divergence correction in the iterative method, the rate of convergence is dramatically improved, and it is particularly useful to compute a model including surface topography in the FD method. Finally, as an example of an airborne EM survey, we present 3D modeling using the FD method.

• Geophysics and Geophysical Exploration
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• v.6 no.1
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• pp.13-22
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• 2003

TSP (Tunnel Seismic Profiling) survey is a technique for imaging and characterizing geological structures ahead of a tunnel face. The seismic modeling algorithm and the synthetic data could be helpful for TSP surveys. However, there is few algorithm to describe the propagation of the elastic waves around the tunnel. In this study, existing 2-dimensional seismic modeling algorithm using finite element method was modified to make a suitable algorithm for TSP modeling. Using this algorithm, TSP modeling was practiced in some models. And the synthetic data was analyzed to examine the propagation characteristics of the elastic waves. First of all, the modeling for the homogeneous tunnel model was practiced to examine the propagation characteristics of the direct waves in the vicinity of the tunnel. And the algorithm was applied to some models having reflector which is perpendicular or parallel to the excavation direction. From these, the propagation characteristics of the reflected waves were examined. Furthermore, two source-receiver arrays were used in respective models to investigate the properties of the two arrays. These modeling algorithm and synthetic data could be helpful in interpreting TSP survey data, developing inversion algorithm and designing new source-receiver arrays.