As one illustrative embodiment, a first calculator obtains a first power value, which is the sum of the absolute value of a plurality of data obtained by a plurality of transmissions. A velocity-vector calculating unit obtains the velocity vector based on a plurality of data. A second calculator obtains a second power value, which is the absolute value of the velocity vector. A post-filter processor comprises one or more post-filter processes to determine the power value, and in the one or more post-filter processes, a power value other than the power value used in obtaining the threshold value for determination is selected as the power value at each observation point and the selected power value is determined based on the threshold value for determination.
