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All Journal Indonesian Journal of Geography Jurnal Matematika & Sains Journal of Mathematical and Fundamental Sciences Journal of Engineering and Technological Sciences Indonesian Journal of Physics (IJP)
Doddy Sutarno
Earth Physics And Complex System Research Group, Faculty Of Mathematics And Natural Sciences, Institut Teknologi Bandung
Astronomy Chemistry Computer Science & IT Earth & Planetary Sciences Electrical & Electronics Engineering Energy Engineering Mathematics Physics

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Pemodelan Magnetotellurik 2D Menggunakan Metode Elemen Batas Imran Hilman Mohammad; Wahyu Srigutomo; Doddy Sutarno
Jurnal Matematika & Sains Vol 16, No 2 (2011)
Publisher : Institut Teknologi Bandung

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Abstract

Dalam permasalahan elektromagnetik untuk aplikasi geofisika, rangkaian persamaan Maxwell dapat disederhanakan menjadi persamaan Helmholtz, sehingga dapat dicari solusi permasalahan menggunakan berbagai skema numerik. Metode elemen batas merupakan metode numerik untuk memecahkan persamaan diferensial parsial yang telah dikembangkan dalam beberapa dekade ini untuk memecahkan berbagai permasalahan medan elektromagnet. Metode ini memiliki keunikan dibandingkan metode numerik lain untuk memecahkan persamaan diferensial parsial, karena hanya membutuhkan diskretisasi pada bidang-bidang batas domain pemodelan. Solusi pada batas domain dapat digunakan untuk mencari solusi pada seluruh  domain pemodelan, membuat metode ini memiliki algoritma numerik yang sangat efisien. Dalam makalah ini, metode elemen batas digunakan untuk menghitung respon magnetotellurik 2D dalam bentuk resistivitas semu dan fasa impedansi modus TE (transverse electric). Pemodelan elemen hingga digunakan sebagai pembanding hasil pemodelan elemen batas yang dikembangkan. Kata kunci : Metode elemen batas, Magnetotelurik 2D.   2D Magnetotelluric Modelling using Boundary Element Method Abstract In most formulations of electromagnetic methods in geophysics, the set of Maxwell’s equations can be simplified into Helmholtz’s equation which leads to possibility of solving electromagnetic problems using various numerical schemes. The boundary element method is a numerical method for solving partial differential problems which in the last several decades has been applied in electromagnetic problems. The method poses unique advantage in comparison to other methods; it requires discretization only on the boundaries of the modeling domain.  Solutions in the boundaries can be used to find solutions on the entire modeling domain, which makes the boundary element method a highly efficient numerical method. This paper will discuss 2D magnetotelluric (MT) modeling using boundary element method. The method is applied to calculate 2D MT responses, expressed in apparent resistivity and phase of impedance, for transverse electric (TE) mode.  The results obtained by the method are compared to those calculated by analytical solution and finite element modeling to show the accuracy of boundary element method. Keywords: Boundary-element method, 2D magnetotelluric.
Global Inversion of Grounded Electric Source Time-domain Electromagnetic Data Using Particle Swarm Optimization Cahyo Aji Hapsoro; Wahyu Srigutomo; Acep Purqon; Warsa warsa; Doddy Sutarno; Tsuneomi Kagiyama
Journal of Engineering and Technological Sciences Vol. 53 No. 1 (2021)
Publisher : Institute for Research and Community Services, Institut Teknologi Bandung

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5614/j.eng.technol.sci.2021.53.1.1

Abstract

Global optimization inversion of grounded wire time-domain electromagnetic (TDEM) data was implemented through application of the particle swarm optimization (PSO) algorithm. This probabilistic approach is an alternative to the widely used deterministic local-optimization approach. In the PSO algorithm, each particle that constitutes the swarm epitomizes a probable geophysical model comprised by subsurface resistivity values at several layers and layer thicknesses. The forward formulation of the TDEM problem for calculating the vertical component of the induced magnetic field is first expressed in the Laplace domain. Transformation of the magnetic field from the Laplace domain into the time domain is performed by applying the Gaver-Stehfest numerical method. The implementation of PSO inversion to the TDEM problem is straightforward. It only requires adjustment of a few inversion parameters such as inertia, acceleration coefficients and numbers of iteration and particles. The PSO inversion scheme was tested on synthetic noise-free data and noisy synthetic data as well as to field data recorded in a volcanic-geothermal area. The results suggest that the PSO inversion scheme can effectively solve the TDEM 1D stratified earth problem. 
Interpretation of 1D Vector Controlled-Source Audio-Magnetotelluric (CSAMT) Data Using Full Solution Modeling Imran Hilman Mohammad; Wahyu Srigutomo; Doddy Sutarno; Prihadi Sumintadiredja
Journal of Mathematical and Fundamental Sciences Vol. 45 No. 2 (2013)
Publisher : Institute for Research and Community Services (LPPM) ITB

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5614/j.math.fund.sci.2013.45.2.7

Abstract

In conventional controlled-source audio-magnetotelluric (CSAMT) prospecting, scalar CSAMT measurement is usually performed because of its simplicity and low operational cost. Since the structure of earth's conductivity is complex, the scalar CSAMT method can lead to a less accurate interpretation. The complex conditions need more sophisticated measurements, such as vector or tensor CSAMT, to interpret the data. This paper presents 1D vector CSAMT interpretation. A full solution 1D CSAMT forward modeling has been developed and used to interpret both vector and scalar CSAMT data. Occam's smoothness constrained inversion was used to test the vector and scalar CSAMT interpretations. The results indicate the importance of vector CSAMT to interpret CSAMT data in complex geological system.
Direct Method Solution of 3-D Magnetotelluric Modeling Using Vector Finite Element Method Rudy Prihantoro; Doddy Sutarno; Nurhasan Nurhasan
Journal of Mathematical and Fundamental Sciences Vol. 51 No. 1 (2019)
Publisher : Institute for Research and Community Services (LPPM) ITB

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5614/j.math.fund.sci.2019.51.1.7

Abstract

As exploration is forced into more difficult areas with complex three-dimensional (3-D) structural environments, the importance of 3-D magnetotelluric (MT) modeling is essential for the correct interpretation of MT data. To reduce the complexity of the calculations introduced by 3-D models, iterative forward calculation of MT response functions is used as basis for inversion of 3-D MT data. This paper proposes an alternative procedure for making reliable 3-D MT modeling codes for forward calculation that is not only effective but also accurate. This is accomplished by using a direct method to solve the linear systems arising from the discretization process in the vector finite element approach. The vector finite element method is known for its capability of overcoming difficulties in modeling caused by possible jumps of normal components across discontinuities of material properties. Meanwhile, by using a direct method rather than an iterative method, the process of solving the linear equations does not suffer from slow convergence. Here, we present a comparison between our modeling codes and codes based on a different approach. In the resulting 3-D MT responses it was found that the proposed method has high accuracy.
Development of Robust Magnetotelluric Impedance Estimation : a Riview Doddy Sutarno
Indonesian Journal of Physics Vol 16 No 3 (2005): Vol. 16 No. 3, July 2005
Publisher : Institut Teknologi Bandung

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (414.419 KB)

Abstract

Robust magnetotelluric (MT) response function estimators are now in standard use by the induction community. Properly devised and applied, these have ability to reduce the influence of unusual data (outliers). The estimators always yield impedance estimates which are better than the conventional least square (LS) estimation because the 'real' MT data almost never satisfy the statistical assumptions of Gaussian distribution and stationary upon which normal spectral analysis is based. This paper reviews the development and application of robust estimation procedures which can be classified as M-estimators to MT data. Starting with the description of the estimators, extensions to MT data analyses are discussed, including utilization of remote reference (RR) sites and the Hilbert Transform (HT) operation on causal MT impedance functions. A recent development of a bounded-influence robust MT impedance estimation is also discussed. The developments are illustrated using synthetic as well as real MT data.
VLF Data Analysis Through Transformation Into Resistivity Value: Application tTo Synthetic and Field Data Wahyu Srigutomo; Asep Harja; Doddy Sutarno; Tsuneomi Kagiyama
Indonesian Journal of Physics Vol 16 No 4 (2005): Vol. 16 No. 4, October 2005
Publisher : Institut Teknologi Bandung

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (917.556 KB)

Abstract

Transformation of VLF-EM signals, which are approximated as the real and imaginary components of the ratio between the vertical and the horizontal components of magnetic fields was carried out in this study to improve the quantitative interpretation aspect of VLF analysis. The transformation filter has been tested using synthetic data generated by a two-dimensional finite element algorithm that provides VLF responses for several models typically encountered in VLF surveys. The transformed apparent resistivity profiles show good agreement in value and pattern to those modeled by the finite element algorithm. The transformation was applied to the field data and further analysis was conducted by inverting the recorded original VLF-EM signals and the transformed apparent resistivity into a two-dimensional resistivity-depth section. From the comparison with the dc-resistivity-depth section obtained previously, the resulted resistivity section revealed the general features of the subsurface structure.
Robust M-Estimation of CSAMT Impedance Functions Doddy Sutarno; Ibnu Fatrio
Indonesian Journal of Physics Vol 18 No 3 (2007): Vol. 18 No. 3 July 2007
Publisher : Institut Teknologi Bandung

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (269.982 KB)

Abstract

Accurate estimation of impedance functions is essential for the correct interpretation of Controlled Source Audio Magnetotelluric (CSAMT) measurements. Noise is inevitably encountered when CSAMT observations are conducted and, consequently, impedance estimates are usually based on least-squares (LS) approximation. Least squares ultimately assume simple Gaussian statistics. However, estimation procedure based on LS would not be statistically optimal, as outliers (abnormal data) are frequently superimposed on a normal ambient CSAMT noise field, which is approximately Gaussian. In this situation, the estimation can be seriously misleading. It is then essential to use statistical procedures that are robust in the sense of being resistant or insensitive to the presence of the outliers. This paper proposes an alternative CSAMT estimation procedure based on M-estimators that is robust and efficient in nature. Like the LS estimate, the M-estimate minimizes the difference between prediction and observation, but differs from the LS estimate in that it defines the measure of misfit in a way that does not allow a few bad points to dominate the estimate. Starting with the description of this estimate, several algorithms for computation are discussed and applied to estimate CSAMT impedance. Using noisy synthetic data, it is shown that the proposed method can produce usable CSAMT impedance functions even under condition of severe noise contamination.
Resistivtiy Structure in Kamojang Geothermal Field Derived from CSAMT Data Enjang Jaenal Mustopa; Wahyu Srigutomo; Doddy Sutarno; Umar Fauzi
Indonesian Journal of Physics Vol 22 No 1 (2011): Vol. 22 No. 1, January 2011
Publisher : Institut Teknologi Bandung

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (307.747 KB) | DOI: 10.5614/itb.ijp.2011.22.1.4

Abstract

Controlled-source audio frequency magnetotelluric (CSAMT) survey consisting of 60 soundings has been carried out in the Kamojang geothermal field to delineate resistivity structure correlated to the present geothermal reservoir. The transmitter site was located about 3 − 5 km in the south-west of the survey area. The sounding sites were distributed irregularly and the distance between each of them varied from 200 to 500 m, covering the Kamojang Geothermal area. The two dimensional (2D) inversion scheme was applied to interpret the CSAMT data. The results show that the subsurface resistivity structures in the Kamojang geothermal field consists of three types of resistivity features correlated to the existing geothermal reservoir in the area, that is, the overburden (first layer) having resistivity value of 30 – 150 ohm.m and thickness of 30 to 100 m overlaying the intermediate (second) layer which has an extremely low resistivity of 3 – 10 ohm.m with 500 – 1200 m thick. This low resistivity layer can be considered as a hydrothermal alteration zone comprising the impermeable layer or sealing cap rock. Finally, the third layer which is relatively more resistive than the second layer with resistivity of 30 − 100 ohm-m. From the 3D view of the low resistivity anomaly (<10 ohm.m) considered as a hydrothermal alteration zone, it is obtained that altered zone is deep in the south-west and becomes shallow in the north-east of the area.
Resistivity Imaging of Mataloko Geothermal Field By Mise-Á-La-Masse Method Enjang Jaenal Mustopa; Wahyu Srigutomo; Doddy Sutarno
Indonesian Journal of Physics Vol 22 No 2 (2011): Vol. 22 No. 2, April 2011
Publisher : Institut Teknologi Bandung

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (616.313 KB) | DOI: 10.5614/itb.ijp.2011.22.2.3

Abstract

Mise-á-la-masse (MAM) measurement has been carried out in the Mataloko geothermal field, Flores, East Nusa Tenggara. The survey was conducted along 16 survey lines in a radial configuration to collect 176 sounding sites. The purpose of the measurement is to image a promising reservoir zone and to correlate the results with the previous geosciences surveys for locating the best drilling target. Three-dimensional (3D) inversion scheme was applied to interpret MAM data. The subsurface resistivity structure obtained from 3D inversion result shows that a low resistivity (1 − 10 ohm.m) structure is widely distributed in the southwest and northeast of the well MT-3/MT-5 at the depth 0 − 100 m. On the other hand, in the deeper part of the survey area, it is recognized that a resistivity in the western part is lower than in the eastern part of the area. The fluid flow tests of well MT-5 produced dry saturated steams of 19.3, 12.6 and 17.4 ton/h at wellhead pressures of 4.0, 6.0, and 5.0 kscg, respectively. Furthermore, the fluid has high enthalpies whose values are 2746, 2755, 2763, 2768, and 2771 kJ/kg at wellhead pressure of 4.0, 5.0, 6.0, 7.0, and 7.5 kscg, respectively. The incorporation of MAM data analyses results with the geosciences data makes it possible to recommend the location of the best target for the drilling site.
Groundwater Vulnerability Comparison Using DRASTIC and GOD Methods in Surakarta City Koesuma, Sorja; Ramelan, Ari Handono; Sutarno, Doddy
Indonesian Journal of Geography Vol 56, No 1 (2024): Indonesian Journal of Geography
Publisher : Faculty of Geography, Universitas Gadjah Mada

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.22146/ijg.87232

Abstract

Demographic growth, urbanization, economic development, agriculture, and consumption per capita have increased the demand for water resources. The population density of Surakarta affects the city’s ability to fulfil its residents’ clean water requirements. As an urban region, Surakarta may be impacted by development activities that degrade the quality and quantity of groundwater. This growing demand should be balanced against effective management of water source regions. This research aims to investigate groundwater vulnerability in Surakarta City. We employed the DRASTIC and GOD methods and compared both results. These methods used the overlay and indexing approaches using GIS based on field data and secondary data such as drill, rainfall, and topographic data. The results of DRASTIC show three types of vulnerability: high (0.21%; 9.87 ha), moderate (94.22%; 4,355.98 ha), and low (5.56%; 257.25 ha), while GOD method results in high (7.03%; 324.96 ha), moderate (52.90%; 2,445.84 ha), low (38.69%; 1,788.81 ha), and negligible (1.37%; 63.49 ha). Based on both methods, we identified Banjarsari district as a location with high groundwater vulnerability. The correlation coefficient between the two methods is 0.511. This value shows that the correlation criteria are acceptable and comparable. This research can be used by local authorities and policymakers to manage groundwater resources. 
Co-Authors Acep Purqon Acep Purqon Ari Handono Ramelan Asep Harja Enjang Jaenal Mustopa Enjang Jaenal Mustopa Fauzi, Umar Hapsoro, Cahyo Aji Ibnu Fatrio Imran Hilman Mohammad Koesuma, Sorja Nurhasan Nurhasan Rudy Prihantoro Sumintadireja, Prihadi Tsuneomi Kagiyama Tsuneomi Kagiyama Wahyu Srigutomo Warsa warsa