With an apparatus according to the invention it is possible to detect an object's velocity transverse to the direction of propagation of an interacting field. Such transverse movement is detected by applying a field that oscillates spatially in the transverse direction. The method used in the apparatus is applicable where wave energy is used to sense or detect an object by its scattering properties when using either sound waves or electro-magnetic waves. The movement can be detected according to the field properties. The field represented by the sampling pulse must feature a spatial oscillation in the directions, where the velocity components are of interest. Such a transversely oscillating field is e.g. generated by using apodization on individual transducer elements and a special focusing scheme. The apparatus uses waves of either sound or electro-magnetic radiation. The temporal characteristics are determined by the setup of the emitter (1). The spatial characteristics are determined by the transmitter array configuration (3) and the receiver array configuration (5) and the respective beam formers (2) and (6a, 6b, 6c). The transmit array consists of $i(N) elements and the receive array consists of $i(M) elements. The transmit beam former and the receive beam former are configured to obtain the spatially oscillating field. The signal received from the interacting objects (4) is processed by the velocity estimator processor (7) for calculation of the velocity vector components by estimating the shift in position as a function of time and the velocity is derived herefrom.