Systems and methods for measuring flow velocities, including ultrasound systems, are provided. A Doppler angle between a direction of ultrasound signals and an axis of a flow may be estimated to improve the accuracy of the flow velocity estimation that is based on Doppler effects. A sensor may be mounted on or in an ultrasound probe to obtain a reference orientation of the ultrasound probe and an orientation of the ultrasound probe relative to the reference orientation when the ultrasound probe is moved to other positions. The Doppler angle may be estimated based on the orientation of the ultrasound probe.
