Aigner Lukas, Högenauer Philipp, Bücker Matthias, Flores Orozco Adrián
Research Unit Geophysics, Department of Geodesy and Geoinformation, Technische Universität Wien, 1040 Vienna, Austria.
Institute of Geophysics and Extraterrestrial Physics, TU Braunschweig, 38106 Braunschweig, Germany.
Sensors (Basel). 2021 Oct 5;21(19):6624. doi: 10.3390/s21196624.
Water-borne transient electromagnetic (TEM) soundings provide the means necessary to investigate the geometry and electrical properties of rocks and sediments below continental water bodies, such as rivers and lakes. Most water-borne TEM systems deploy separated magnetic transmitter and receiver loop antennas-typically in a central or offset configuration. These systems mostly require separated floating devices with rigid structures for both loop antennas. Here, we present a flexible single-loop TEM system, the light-weight design of which simplifies field procedures. Our system also facilitates the use of different geometries of the loop antenna permitting to adjust the depth of investigation (DOI) and the minimum sounding depth in the field. We measure the turn-off ramp with an oscilloscope and use the DOI to assess the minimum and maximum exploration depth of our single-loop TEM system, respectively. A reduction of the loop-antenna size improves early-time TEM data due to a reduced length of the turn-off ramp, whereas an increase of the loop-antenna size enhances the signal strength at late times, which allows to investigate deeper structures below the lake bed. We illustrate the capabilities of our system with a case study carried out at Lake Langau in Austria. Our results show that our system is capable of reaching a DOI of up to 50 m (with a maximum radius of the circular loop of 11.9 m), while it also resolves the water layer down to a minimum thickness of 6.8 m (when the radius is reduced to 6.2 m).
水上瞬变电磁（TEM）测深提供了一种必要手段，用于研究大陆水体（如河流和湖泊）下方岩石和沉积物的几何形状及电学性质。大多数水上TEM系统采用分离式磁发射器和接收器环形天线，通常呈中心或偏移配置。这些系统大多需要为两个环形天线配备带有刚性结构的分离式漂浮装置。在此，我们展示一种灵活的单环TEM系统，其轻量化设计简化了野外作业流程。我们的系统还便于使用不同几何形状的环形天线，从而能够在野外调整探测深度（DOI）和最小测深深度。我们用示波器测量关断斜坡，并分别使用DOI来评估我们单环TEM系统的最小和最大勘探深度。减小环形天线尺寸会因关断斜坡长度缩短而改善早期TEM数据，而增大环形天线尺寸则会增强晚期信号强度，这使得能够探测湖床下方更深的结构。我们通过在奥地利朗高湖进行的一个案例研究来说明我们系统的能力。我们的结果表明，我们的系统能够达到高达50米的DOI（圆形环的最大半径为11.9米），同时还能分辨出最小厚度为6.8米的水层（当半径减小到6.2米时）。
