A vehicle radar sensor unit (2) arranged to acquire a plurality of radar detections, and including an antenna arrangement (3), a transmitter unit (4), a receiver unit (5) and a processing unit (6). The antenna arrangement (3) has at least two transmitter antennas (7, 8) and at least two receiver antennas (9, 10, 11, 12), where two transmitter antennas (7, 8) have a vertical spacing (h) between their respective phase centers (17, 18) that exceeds half the free-space wavelength of the transmitted signal. The processing unit (5) is arranged to determine a first radial velocity of each radar detection by tracking the change of radial distance (r) to each radar detection for a plurality of radar cycles; determine a second radial velocity that best matches the first radial velocity; track a plurality of measured heights (z) as a function of radial distance (r); and to choose a measured height (zGT) among the tracked measured heights (z) that has a minimal change from radar cycle to radar cycle.