1. Method for determining a navigation speed of a carrier by a hybridization device ( 1 ) including a Kalman filter ( 3 ) developing a hybrid navigation speed (V ref ) from inertial measurements calculated by a virtual platform ( 2 ) estimating a speed of the carrier ({circumflex over (V)}) and frequency measurements outputted by a Doppler radar ( 4 ) having a multi-lobe antenna built therein such that a Doppler frequency (F 1 , F 2 , F 3 , F 4 ) is associated with each of the lobes, wherein said method includes the following steps: estimating, from the estimated speed ({circumflex over (V)}), frequencies ({circumflex over (F)} 1 ,{circumflex over (F)} 2 ,{circumflex over (F)} 3 ,{circumflex over (F)} 4 ) corresponding to each of the Doppler frequencies (F 1 , F 2 , F 3 , F 4 ) outputted by the radar, determining a group of observations where each observation represents an estimation deviation on the Doppler frequency associated with a lobe, calculating, by the Kalman filter ( 3 ), a speed correction (ΔV) to be applied to the estimated speed ({circumflex over (V)}) on the basis of the group of observations.