Frequency Difference of Arrival (FDOA) techniques rely on which characteristics?

• A. Doppler difference; collection sensor in motion; creates ISODOP; 2 sensors yield 1 ISODOP, 3 yield 2; Best when sensor velocities similar
• B. Time difference yields an isochrone
• C. Requires stationary sensors
• D. Is independent of carrier frequency

Answer: (A)

FDOA relies on the Doppler difference observed when receivers are in motion relative to the transmitter. Each moving sensor sees a different Doppler shift depending on its velocity along the line of sight to the source, so the difference between the Doppler measurements across sensors defines an isodoppler locus on the surface where the source could lie. With two sensors you get one ISODOP; with three sensors you obtain two independent ISODOP curves, and their intersection helps pinpoint the source more accurately. This approach depends on sensor motion, so stationary sensors don’t produce the same Doppler-difference geometry. It also tends to work best when the sensors have similar velocities, because large disparities can distort the Doppler differences and make the locus harder to interpret.