A Unique Long-term Monitoring Transient Electromagnetic Dataset

We present the first long-term monitoring dataset collected using a transient electromagnetic (TEM) instrument specifically designed for geophysical monitoring applications. The dataset consists of 762 measurements acquired between January 19^th, 2023, and September 05^th, 2025, from the island of Falster, southwestern part of Denmark, an area where saltwater intrusion is a recurring issue. The dataset displays a high consistency throughout the period, which is the foundation for a reliable interpretation over time. The dataset provides a valuable opportunity for researchers to test and validate advanced TEM inversion algorithms, including deterministic, Monte Carlo or probabilistic inversion algorithms, thereby contributing to the advancement of time-lapse studies using TEM methods.