Abstract: There is provided a scintillometer for the measurement of the structure function constant and the inner scale of atmospheric refractive index fluctuations including a transmitter unit with a source emitting radiation. Included in the transmitter unit is a piece of birefringent material which splits the radiation into two displaced orthogonally polarized components. A receiver unit which substantially contains two detectors receives the two components of the radiation. The detectors are combined with polarizers in such a way that at least one detector has a preferred sensitivity to one polarization component and the apparent distance of the detectors in the plane perpendicular to the propagation direction approximately equals the beam displacement produced at the transmitter.