Xu, Yang, et al. “Non-Intrusive Flowrate Measurement and Monitoring System of Plant-Protection Unmanned Aircraft Systems Based on Pump Voice Analysis”. International Journal of Agricultural and Biological Engineering, vol. 14, no. 3, June 2021, pp. 58-65, https://ijabe.migration.pkpps03.publicknowledgeproject.org/index.php/ijabe/article/view/5508.