This paper presents expansion and the behavior of the radar Doppler signals. As the experimental basis for this research work measurement results of the Federal Physical Engineering Bureau, Germany are used. The exposed problem is analyzed from the metrological and the identification point of view, taking the vehicle as the small velocity target under the scope. The comparative analysis of the Doppler signal orthogonal transformations is also presented, comparing the spectrums of different vehicles moving in the electromagnetic field of the Doppler radar with proposed velocities, under strictly defined circumstances. The short time spectrums are related to the photographic picture series taking the optical lenses with the same space angle as the Doppler radar main lob space angle.