Wahyu Srigutomo

Scanning electron microscopy and magnetic characterization of iron oxides in solid waste landfill leachate

Leachate sludge samples were taken from two municipal solid waste sites of Jelekong and Sarimukti in Bandung, Indonesia. Their magnetic mineralogy and granulometry were analyzed to discriminate the sources of magnetic minerals using X-ray diffraction (XRD), scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy (SEM-EDX) and rock magnetism. SEM-EDX analyses infer that the main magnetic minerals in the leachate sludge are iron oxides. In terms of their morphology, the grains from Jelekong are mostly octahedral and angular, which are similar to the general shapes of magnetic grains from the local soils. The grains from Sarimukti, on the other hand, are dominated by imperfect spherule shapes suggesting the product of combustion processes. Hysteresis parameters verify that the predominant magnetic mineral in leachate sludge is low coercivity ferrimagnetic mineral such as magnetite (Fe(3)O(4)). Furthermore, comparisons of rock magnetic parameters show that the magnetic minerals of soil samples from Jelekong have higher degree of magnetic pedogenesis indicating higher proportion of superparamagnetic/ultrafine particles than those of soil samples from Sarimukti. The plot of susceptibilities ratio versus coercive force has a great potential to be used as a discriminating tool for determining the source of magnetic minerals.

Measurement of gravitational acceleration using a computer microphone port

A method has been developed to measure the swing period of a simple pendulum automatically. The pendulum position is converted into a signal frequency by employing a simple electronic circuit that detects the intensity of infrared light reflected by the pendulum. The signal produced by the electronic circuit is sent to the microphone port and recorded as a 16-bit wave file by common software. The wave file is then processed to obtain the signal period as a function of time by timing all zero crossings. From the obtained signal period as a function of time, an average value of the period is calculated. Using the calculated average period, it was found that the gravitational acceleration is (9.77 ± 0.03) m s−2. Noting that the G-type La Coste & Romberg G928 gravimeter obtains a gravitational acceleration of 9.78 m s−2, the present method offers very good accuracy, with a percentage error of about 0.1%.

Thermal modeling and heat flow density interpretation of the onshore Northwest Java Basin, Indonesia

Studies pertaining to heat flow density distribution in Indonesian tertiary sedimentary basins have been conducted intermittently throughout more than two decades. Even so, all of these studies have always concentrated on the basic compilations of thermal gradient, thermal conductivity, and terrestrial heat flow datasets or the study of basin thermal history rather than on the investigations into their present thermal regime. In addition, syntheses on the possible causes to the observed heat flow density distribution in these basins have been largely determined only on the basis of its correlation with geological and geophysical evidences. One basin experiencing this particular problem is the onshore Northwest Java Basin, where knowledge of the present-day subsurface temperature structure is virtually absent and interpretation of heat flow distribution has been mainly qualitative. For these reasons, in this study we have attempted to quantitatively characterize the present subsurface temperature distribution and surface heat flow density of the onshore Northwest Java Basin using a simple numerical thermal modeling approach, based on the most recent heat flow datasets. Taking into account a conductive heat transfer process, the modeling exercise is aimed at deriving a 3-D subsurface temperature distribution. The temperature distribution is translated into the predicted surface heat flow distribution. The modeled temperature field reveals its dependence on the geometrical aspects of the basin’s basement. Comparison between the computed and the observed heat flow densities, taking into account the uncertainties of both, suggests that advective heat transport by groundwater flow may be present, in addition to conduction. The modeling results are thus capable of demonstrating the importance of a quantitative approach in studying the present thermal state of a sedimentary basin.

Development of alternating current transmitter of detection system for magnetic material in soil subsurface

Generally, detection system for magnetic material in soil subsurface using electromagnetic induction method consists of two parts, they are transmitter and receiver unit. A transmitter must be able to produce a continuous and stable AC current at a certain frequency, meanwhile receiver should be able to catch the secondary magnetic field of magnetic material in soil subsurface. The aim of this study was to develop a new AC current transmitter of detection system for the magnetic material in soil subsurface. This paper will describe the results of the development of AC current transmitter systems, distance characterization of the sensor detection toward horizontal solenoid positions, and characterization of magnetic material in the soil subsurface. It has successfully made the AC current transmitter system, composed of a sinusoidal signal generator, power amplifier, and a source of AC magnetic field. The output of the generator has a frequency varies: 1 kHz, 2 kHz, 5 kHz, and 10 kHz. We found that the AC c...

Location and Pressures Change Prediction of Bromo Volcano Magma Chamber Using Inversion Scheme

Bromo volcano is one of active volcanoes in Indonesia. It has erupted at least 50 times since 1775 and has been monitored by Global Positioning System (GPS) since 1989. We applied the Levenberg-Marquardt inversion scheme to estimate the physical parameters contributing to the surface deformation. Physical parameters obtained by the inversion scheme such as magma chamber location and volume change are useful in monitoring and predicting the activity of Bromo volcano. From our calculation it is revealed that the depth of the magma chamber d = 6307.6 m, radius of magma chamber α = 1098.6 m and pressure change ΔP ≈ 1.0 MPa.

2D Resistivity and Induced Polarization Measurement for Manganese Ore Exploration

2D Resistivity and Induced Polarization (IP) survey was conducted to delineate the presence of minerals containing manganese in form of manganese ore. The resistivity method concerns with resistivity (ohm.m) of rocks which indicates the electrical properties in terms of ability to resist the flow of electrical current. The presence of manganese in rocks generally lowers the resistivity. The Induced Polarization (IP) method deals with chargeability (in msec) which indicates the strength of polarization effects experienced by ions in the vicinity of metallic grains in rock. The presence of manganese in rocks increases the chargeability of the rock when measured using IP method. The low resistivity zones ( 10 msec).

High Sensitivity Fluxgate Sensor for Detection of AC Magnetic Field: Equipment for Characterization of Magnetic Material in Subsurface

A magnetic material characterization at subsurface of soil using portable controlled source electromagnetic (CSEM) methods needs a continuous signal which has frequency more than 1 kHz. This signal can be obtained from the function generator which its output was amplified by a power amplifier with a gain of 16 times. The AC output current of the power amplifier can be varied from 0.1 A 0.45 A at frequency of 5 kHz. To generate an AC magnetic field, the output of the power amplifier is then connected to the solenoid with a ferrite-core coils number of 130 and diameter of 3 cm. The AC magnetic field was detected by fluxgate sensor with high sensitivity (568 mV/μT or 1.76 nT/mV). By adjusting the excitation and phase detector frequency in the electronic circuits of fluxgate sensor, will enable this sensor work at higher frequency. The signal processing circuit of fluxgate sensor uses the 2nd-order of Butterworth filter with frequency scaling factor of 10.6 kHz. By this method fluxgate sensor can detect the AC magnetic field frequency up to 10 kHz. The output voltage of this sensor has a maximum measurement range of 0.23 2.95 V at frequency of 5 kHz. Meanwhile, the minimum detectable magnetic field is 1.5 μT; with a relative error of measurement was 2.74 %.

A complete quantitative analysis of self-potential anomaly using singular value decomposition algorithm

A new quantitative interpretation method of self potential anomaly related to geometric-shaped models such as horizontal cylinder, vertical cylinder, and sphere object has been proposed in this paper. This method is based on the concept of solving least-squares algorithm with singular value decomposition approach which is designed and implemented to calculate the depth, the electric dipole moment, the polarization angle, and the geometric shape factor of self potential anomaly. This approach uses singular value decomposition algorithm to solve non-linear inversion of self potential anomaly. The singular value decomposition algorithm was randomly tested on theoretical synthetic data which was generated by a chosen statistical distribution from a known model with different random noise level. The result shows there is a close agreement between the assumed and calculated parameters. Finally the method validity is tested on the real self potential data anomaly which is obtained from a cylindrical object that was buried at certain depth.

Resistivtiy Structure in Tangkuban Parahu Area Drived from CSAMT Data

Tangkuban Parahu is located in Bandung, West Java, one of a volcano area. Controlled-source audio frequency magnetotelluric (CSAMT) survey has been conducted in the area using transmitter located in 3-5 km from the survey area. The objective of the survey was to determine a subsurface resistivity structures that may correlate to a geothermal reservoir in unknown geothermal potential area. In the paper, we applied a two-dimensional (2D) inversion scheme to interpret of the CSAMT data to obtain several resistivity sections describing the subsurface resistivity structures. The results of 2D inversion indicated several subsurface low resistivity anomaly (1-10 ohm.m) in the depth of 1000-1500 meter that may correlate to the existing a geothermal reservoirir confirmed by several surface manifestations in the area.

1-D DC Resistivity Inversion Using Singular Value Decomposition and Levenberg-Marquardt’s Inversion Schemes

Exploration of natural or energy resources requires geophysical survey to determine the subsurface structure, such as DC resistivity method. In this research, field and synthetic data were used using Schlumberger configuration. One-dimensional (1-D) DC resistivity inversion was carried out using Singular Value Decomposition (SVD) and Levenberg-Marquardt (LM) techniques to obtain layered resistivity structure. We have developed software to perform both inversion methods accompanied by a user-friendly interface. Both of the methods were compared one another to determine the number of iteration, robust to noise, elapsed time of computation, and inversion results. SVD inversion generated faster process and better results than LM did. The inversion showed both of these methods were appropriate to interpret subsurface resistivity structure.