Hendra Grandis
Graduate Program in Geophysical Engineering, Institut Teknologi Bandung Jalan Ganesha 10, Bandung, 40132, Indonesia Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung Jalan Ganesha 10, Bandung, 40132, Indonesia

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Quasi-2D Resistivity Model from Inversion of Vertical Electrical Sounding (VES) Data using Guided Random Search Algorithm

Journal of Mathematical and Fundamental Sciences Vol 47, No 3 (2015)
Publisher : ITB Journal Publisher, LPPM ITB

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Abstract

Vertical electrical sounding (VES) data are usually interpreted in terms of a 1D resistivity model using linearized inversion. The local approach of a non-linear inverse problem has fundamental limitations, i.e. the necessity of a starting model close to the solution and possible convergence to a local rather than a global minimum solution. We studied the application of a global search approach for non-linear inversion using the guided random search method to model VES data. A quasi-2D resistivity model can be created by stitching 1D models obtained from VES data along a profile. Both vertical and lateral resistivity variations are minimized to incorporate a 2D smoothness constraint. The proposed method was applied to invert synthetic VES data as well as field data from a sedimentary environment. Both synthetic and field data inversions resulted in models that correlated well with the known synthetic model and with the geology of the study area, respectively.

Aplikasi Metode Inversi Damped Least-square untuk Pemodelan 1-D Data TEM

Jurnal Lingkungan dan Bencana Geologi Vol 6, No 2 (2015)
Publisher : Badan Geologi

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Abstract

ABSTRAKMetode TEM (transient electromagnetic) merupakan metode alternatif yang dapat digunakan untuk mencari sumber air tanah selain metode geolistrik. Prinsip metode TEM adalah menginduksikan energi elektromagnetik ke dalam tanah dengan menggunakan transmitter loop dan receiver koil yang merekam respon bawah permukaan ketika transmitter dalam keadaan mati (tidak ada medan primer). Pemodelan data TEM pada umumnya masih menggunakan model 1-D. Penelitian ini akan membahas mengenai metode Inversi damped least-square untuk pemodelan inversi 1-D dari data TEM. Metode damped least-square membutuhkan parameter model awal untuk selanjutnya dilakukan inversi damped least-square menggunakan teknik SVD (Singular Value Decomposition). Metode ini diaplikasikan terhadap tiga data sintetik. Data sintetik I menunjukkan nilai resistivitas semakin kecil seiring bertambahnya kedalaman. Data sintetik II menunjukkan nilai resistivitas semakin besar seiring dengan bertambahnya kedalaman. Data sintetik III merupakan respon model yang mewakili daerah prospek airtanah, memperlihatkan lapisan konduktif diapit oleh lapisan resistif dan sebaliknya. Metode damped least-square juga diaplikasikan pada data lapangan daerah karst Kabupaten Tuban. Hasil pemodelan data sintetik memperlihatkan kesesuaian yang optimum antara data resistivitas semu observasi dan perhitungan. Sedangkan, hasil pemodelan data lapangan memerlihatkan kesesuaian model dengan kondisi geologi setempat.Kata kunci: metode damped least-square, singular value decomposition dan transient electromagnetic.ABSTRACTTransient electromagnetic (TEM) sounding method is an alternative method other than the geoelectrical method that can be used for groundwater exploration purposes. The principle TEM method is done by the induction of electromagnetic fields at the surface within a transmitter loop and record the subsurface response in the receiever coil when the absence of the primary field (transmitter off). TEM data are usually interpreted in term of 1-D model. The damped least-square method is presented in this paper. The damped least-square method needs an initial model parameter and employs the damped least-square solution with Singular Value Decomposition (SVD) technique. This methods have been applied to three synthetic data sets. The first synthetic data shows decreasing resistivities with depth. The second synthetic data shows increasing resistivities with depth. The third synthetic data are a response of groundwater prospect model, consisting of a conductor layer between two resistors and resistor layer between two conductors. Damped least-square methods was also applied to field data from karst area, Tuban. The results from synthetic data inversions presented good fit between the observed and the calculated apparent resistivity data. The results from field data show models subsurface resistivity consistent with the local geology.Keyword : damped least-square method, singular value decomposition and transient electromagnetic.