A Doppler radar detects precipitation targets via the reflected radar signal (providing information on precipitation location and intensity) and measures the Doppler frequency shift of the returned signal to determine the radial velocity component of targets moving toward or away from the radar antenna (along the direction of the radar beam); however, because Doppler radar can only measure the velocity component along the radar beam (the radial component), it cannot detect wind or precipitation motion that is purely perpendicular to the beam direction (i.e., blowing tangentially, parallel to the antenna's line of sight direction at a given azimuth), since such motion produces no radial velocity component and therefore no Doppler shift.