Noise Reduction for Transient Electromagnetic with High Cultural Noise: Case Study in Cisarua, Bandung Barat Regency

Transient Electromagnetic data acquisition was conducted in Cisarua, Bandung Barat Regency. Data are acquired using grounded dipole transmitter 500 meter spaced, with 13 A of current injected. TEM period are 40 s with 102 measurement period in total. Magnetic impedance sensor as receiver measured vertical magnetic field, located 400 meter from transmitter center point. The measurement area was located in a residential area and very close to man-made electromagnetic noise sources including power lines, radio and cellular transmitters. Periodic noise recorded along with transient signal was very strong, where the amplitude of 50 Hz noise is higher than the transient signal even at early time. This poses a challenge where a technique that capable of reducing noise and reconstructing the transient data are needed, so the data can further be processed in inversion program to create subsurface model. First technique used was statistical selection which is simple but proven effective in reducing noise in this condition without distorting the data. Data processing then continued by applying digital notch filter. After the transient signal are obtained, smoothness constrained least-square inversion are used to get the subsurface resistivity model, which shows 2 low resistivity zone. The shallower zone was supported by Electrical Resistivity Tomography data, and interpreted as shallow unconfined aquifer. The deeper zone was taught to be old volcanic products saturated with water associated with fault in the eastern area. (paper)