  We consider the matterwave interferometric measurement of atomic velocities,
which forms a building block for all matterwave inertial measurements. A
theoretical analysis, addressing both the laboratory and atomic frames and
accounting for residual Doppler sensitivity in the beamsplitter and recombiner
pulses, is followed by an experimental demonstration, with measurements of the
velocity distribution within a 20 $\mu$K cloud of rubidium atoms. Our
experiments use Raman transitions between the long-lived ground hyperfine
states, and allow quadrature measurements that yield the full complex
interferometer signal and hence discriminate between positive and negative
velocities. The technique is most suitable for measurement of colder samples.
