关键词: 大地电磁观测, 强电磁干扰, 远参考处理, 非Robust

Abstract:

With the development of national economic construction, high-speed railway, wind power stations, and photovoltaic power stations, large-scale high voltage power grids are widely distributed. Under these strong electromagnetic interference environments, obtaining high-quality magnetotelluric(MT)observation data is a practical problem. We carried out MT observation in Yinchuan, Yuncheng, Hebi, and Zhangjiakou in the past two years, and based on the data acquisition and processing results of around 500 MT stations in these four survey areas, 45 typical MT stations under strong electromagnetic interference environments are selected. Based on the nearest interference source, we sorted out these stations into seven kinds of strong electromagnetic interference environment. The seven kinds of strong electromagnetic interference environment are high-speed railway(0.5~1km), electrified railway(1.3~3.7km), wind power station(0.1~3.7km), photovoltaic power station(2~9km), large-scale high voltage power grids(0.06~0.4km), colliery(0.15~1km), and city(0.05~0.8km). The apparent resistivity curve obtained from processing of the typical MT station’s original data shows that the electromagnetic interference near the high-speed railway, electrified railway, and photovoltaic power station is mainly near-field interference. The mid-band frequency apparent resistivity curve of MT stations under near-field interferences rises along an angle of 45° while the impedance phase curve tends to 0. The electromagnetic interference of wind power generation facilities on MT data is relatively small. Large-scale high voltage power grids, colliery, and urban integrated electromagnetic interference are reflected in the apparent resistivity curve as discrete “outlier” with single or multiple frequency points. The curve does not have a stable shape at all. For the 45 typical MT stations listed in this paper under the strong electromagnetic interference environment, the data collection time covers two nights. The use of remote reference, non-robust processing, and fine spectrum selection for the full-time time series data improves MT data quality. The process of obtaining effective spectrum data and the results show that to get effective magnetotelluric data in a strong electromagnetic interference environment, the MT data observation time should include at least two nights(41h). Secondly, when the seven types of strong electromagnetic interference cannot be avoided, the MT stations should be placed at a distance of no less than 0.5km from high-speed railways, 1.3km from electrified railways, 2km from photovoltaic power stations, 0.2km from large-scale high voltage power grids, and 0.3km from colliery. It is also recommended that the distance of MT station shall be no less than 0.2km from electric wires, no less than 0.3km from transformers, and no less than 0.5km from thermal power stations in the comprehensive urban disturbance. The wind power stations have little effect on magnetotelluric data. Finally, a high-quality remote reference shall be used in the data processing. The use of this data can effectively suppress the influence of electromagnetic near-field interference by performing remote reference processing and estimating the spectrum data with the non-robust method.

Key words: magnetotelluric observation, strong electromagnetic interference, remote-reference, non-robust