## 1 Introduction  
In recent years, the coal industry has undergone significant consolidation and restructuring, resulting in the closure of numerous small coal mines lacking safe production conditions. Many of these mines lack proper geological data and have abandoned areas, posing a serious safety hazard to coal mining operations. Therefore, the timely identification of accumulated water within the coal mining area is crucial for ensuring safe coal production [1]. The transient electromagnetic method (TEM) is the preferred technique for hydrogeological exploration in coal mines due to its ability to detect low-resistivity anomalies effectively. It is commonly employed to delineate water-rich zones in coal seam aquifers, assess the conductivity and water content of geological structures, and identify water-rich areas and channels in goat regions. During field operations, two main types of devices are utilized: the central loop and the large fixed transmitter. The central loop device exhibits a strong coupling with geological formations, yielding optimal detection results despite lower operational efficiency. Conversely, the large fixed source device offers higher efficiency and greater detection depth but may not couple with geological formations as effectively as the central loop device [2]. In the mineral-rich western regions of China characterized by rugged terrain, traditional TEM surveys using loop sources face challenges. The proliferation of dense vegetation due to environmental restoration efforts limits the space for loop source construction. Moreover, rapid rural development introduces additional noise and interference, necessitating enhanced convenience and reliability in TEM field operations [3]. Small-loop devices in TEM surveys typically employ square loops ranging from several to dozens of meters in size as emission sources. To maintain the excitation energy of the primary field, multiple turns, varying from several to dozens, are commonly utilized. Their construction flexibility and adaptability to different sites have garnered increasing attention in recent years [3]. The small-loop device can be categorized into mine TEM and shallow TEM based on the working environment. This study primarily focuses on shallow TEM applications in ground exploration. Notably, this device has demonstrated significant achievements in coal mine old kiln detection, mineral exploration, reservoir leakage detection, geotechnical engineering investigations, and shallow karst development identification [4; 5; 6; 7; 8; 9]. In 1994, [PERSON] and colleagues from Xi'an Research Institute Co. Ltd. (Xi'an, China) and China Coal Technology and Engineering Group Corp (CCTGE, Xi'an, China) conducted old kiln detection tests in Mentougou, Beijing using small-loop TEM [10]. The results indicated successful detection up to approximately 150 m, effectively revealing the spatial position of the old kiln [10]. Subsequently, the device was employed in a Xinjiang coal mine to detect old kilns and coal seam combustion areas up to 200 m deep, yielding satisfactory detection outcomes and confirming the feasibility of deep detection with small-loop devices [11]. However, there was a scarcity of relevant research on shallow small-loop TEM until [PERSON] et al. utilized a 10 m \(\times\) 10 m high-current emission wire frame for bauxite exploration in 2007, validating its applicability in this context [5]. In the following year, [PERSON] et al. conducted a successful exploration in the Dachang gold prospecting area and Suolagou silver ore area in Qinghai Province using a 5 m \(\times\) 5 m emission line frame, highlighting the high lateral resolution advantage of small-loop TEM [6]. Over the past decade, shallow small-loop TEM has found widespread application in coal mine goat exploration. Researchers have employed various configurations, such as a 16-turn 4 m \(\times\) 4 m small-loop TEM device, in Inner Mongolia to delineate coal mine accumulated goats up to 136 m deep [2].