Purwanto, M. S., A. Susilo, A. Naba, A. S. Bahri, and S. Navisa. “Integration of Principal Component Analysis and Very Low Frequency Geophysical Method for Modeling Recharge Area Distribution: The Case Study of Krawak Spring, Tuban”. Engineering, Technology & Applied Science Research, vol. 15, no. 3, June 2025, pp. 22644-62, doi:10.48084/etasr.10508.