Drone-towed controlled-source electromagnetic (CSEM) system for near-surface geophysical prospecting: on instrument noise, temperature drift, transmission frequency, and survey set-up

IF 1.8 4区地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY

Geoscientific Instrumentation Methods and Data Systems Pub Date : 2022-12-08 DOI:10.5194/gi-11-435-2022

Tobias Bjerg Vilhelmsen, A. Døssing

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引用次数: 1

Abstract

Abstract. Drone-borne controlled-source electromagnetic (CSEM) systems combine the mobility of airborne systems with the high subsurface resolution in ground systems. As such, drone-borne systems are beneficial at sites with poor accessibility and in areas where high resolution is needed, e.g. for archaeological or subsurface pollution investigations. However, drone-borne CSEM systems are associated with challenges, which are not observed to the same degree in airborne or ground surveys. In this paper, we explore some of these challenges based on an example of a new drone-towed CSEM system. The system deploys a multi-frequency broadband electromagnetic sensor (GEM-2 uncrewed aerial vehicle, UAV), which is towed 6 m below a drone in a towing-bird configuration together with a NovAtel GNSS–IMU (global navigation satellite system–inertial measurement unit) unit, enabling centimetre-level position precision and orientation. The results of a number of controlled tests of the system are presented together with data from an initial survey at Falster (Denmark), including temperature drift, altitude vs. signal, survey mode signal dependency, and the effect of frequency choice on noise. The test results reveal the most critical issues for our system and issues that are likely encountered in similar drone-towed CSEM set-ups. We find that small altitude variations (± 0.5 m) along our flight paths drastically change the signal, and a local height vs. signal correlation is needed to correct near-surface drone-towed CSEM data. The highest measured impact was −46.2 ppm cm−1 for a transmission frequency of 91 kHz. We also observe a significant increase in the standard deviation of the noise level up to 500 % when going from one transmission frequency to five. We recommend not to use more than three transmission frequencies, and the lowest transmission frequencies should be as high as the application allows it. Finally, we find a strong temperature dependency (up to 32.2 ppm∘C-1), which is not accounted for in the instrumentation.

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近地表地球物理勘探用无人机拖曳可控源电磁系统:仪器噪声、温度漂移、传输频率和测量设置

摘要无人机控制源电磁（CSEM）系统将机载系统的机动性与地面系统的高地下分辨率相结合。因此，无人机携带的系统在可达性差的地点和需要高分辨率的地区是有益的，例如用于地质或地下污染调查。然而，无人机携带的CSEM系统与挑战有关，在空中或地面调查中没有观察到同样程度的挑战。在本文中，我们以一个新型无人机拖曳CSEM系统为例，探讨了其中的一些挑战。该系统部署了一个多频宽带电磁传感器（GEM-2无人机），该传感器被拖曳6 m以下的无人机，采用拖曳鸟配置，以及NovAtel GNSS–IMU（全球导航卫星系统-惯性测量单元）单元，实现厘米级的位置精度和定向。该系统的一系列受控测试结果与Falster（丹麦）的初步调查数据一起提供，包括温度漂移、海拔高度。信号，调查模式信号相关性，以及频率选择对噪声的影响。测试结果揭示了我们系统最关键的问题，以及在类似的无人机拖曳CSEM设置中可能遇到的问题。我们发现小的海拔变化（± 0.5 m）沿着我们的飞行路线，信号发生了巨大变化，需要进行局部高度与信号的相关性，以校正近地面无人机拖曳的CSEMdata。测得的最高冲击为−46.2 ppm cm−1，传输频率为91 kHz。我们还观察到噪音水平的标准偏差显著增加，最高可达500 % 当从一个传输频率变为五个时。我们建议不要使用超过三个传输频率，最低传输频率应尽可能高。最后，我们发现温度依赖性很强（高达32.2 ppm∘C-1），这在仪器中没有考虑。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Geoscientific Instrumentation Methods and Data Systems GEOSCIENCES, MULTIDISCIPLINARYMETEOROLOGY-METEOROLOGY & ATMOSPHERIC SCIENCES

CiteScore

3.70

自引率

0.00%

发文量

审稿时长

37 weeks

期刊介绍： Geoscientific Instrumentation, Methods and Data Systems (GI) is an open-access interdisciplinary electronic journal for swift publication of original articles and short communications in the area of geoscientific instruments. It covers three main areas: (i) atmospheric and geospace sciences, (ii) earth science, and (iii) ocean science. A unique feature of the journal is the emphasis on synergy between science and technology that facilitates advances in GI. These advances include but are not limited to the following: concepts, design, and description of instrumentation and data systems; retrieval techniques of scientific products from measurements; calibration and data quality assessment; uncertainty in measurements; newly developed and planned research platforms and community instrumentation capabilities; major national and international field campaigns and observational research programs; new observational strategies to address societal needs in areas such as monitoring climate change and preventing natural disasters; networking of instruments for enhancing high temporal and spatial resolution of observations. GI has an innovative two-stage publication process involving the scientific discussion forum Geoscientific Instrumentation, Methods and Data Systems Discussions (GID), which has been designed to do the following: foster scientific discussion; maximize the effectiveness and transparency of scientific quality assurance; enable rapid publication; make scientific publications freely accessible.