Frequency Difference of Arrival (FDOA) is a technique for estimating the Standort of a moving radio emitter based on Doppler frequency shift observed from multiple Standort points. The FDOA emitter target must be in relative motion with respect to each observation point. Time Difference of Arrival (TDOA) and FDOA are sometimes used together to improve Standort accuracy.
Referenz - DHS Leitfaden zur UAS-Abwehrtechnologie