Perpustakaan Digital ITB

Time constant maps are widely used as a preliminary interpreting tool and effective means for data quality assessment in helicopter transient electromagnetic (HTEM) surveys. It can be used to quickly and qualitatively indicate the distribution of geological anomalies. A new time constant method, called Principal Time Constant (PTC) method, is proposed in this paperwhich directly processed the linear sampled data and can provide an unbiased estimation of time constant compared with the traditional methods, Apparent Time Constant (ATC) method and Sliding Time Constant (STC) method. In order to estimate the performance and stability of these three methods, Monte Carlo simulations have been used with different signal to noise ratios. The simulation results show that the time constant estimated by the PTC method is closer to the true value than that by the ATC and STC methods and the variance of time constant evaluated by the PTC method is closer to the Cramer-Rao Low Boundary, which shows that the PTC method has the most stable performance in the time constant estimation. To verify the effectiveness of the PTC method, a field surveywas conducted in Inner Mongolia by the HTEM system for measured data. The time constant maps, produced by different methods respectively, are consistent with the local geology of the survey area in general. However, the map produced by the PTC method has a higher contrast of the time constant value for different targets and shows better consistency with the geological map. The following quantitative insight of resistivity-depth slice also verifies the features revealed in the time constant map, which proves the effectiveness of the time constant map produced by the PTC method