| abstract |
A velocimeter having: a source of coherent radiation directed to irradiate a surface from which the relative velocity is to be measured; a receiver for the resulting reflection of coherent radiation from said surface, the receiver including a receiving aperture and a photodetector responsive to the reflected radiation passing through the aperture; a drive to translate the aperture, and; circuitry to indicate the frequencies of the signals generated by the photodetector when the aperture is stationary in relation to the photodetector and when the aperture is translated in relation to said photodetector. The velocimeter determines the magnitude and the direction of the velocity vector it measures. A navigation velocimeter, using the described velocimeter, is disclosed for use in an aircraft to determine the direction and magnitude of the velocity vector of the aircraft with respect to the ground. The aperature hereinabove mentioned is preferably a plurality of slits, alternately transparent and opaque, such as in a transmission type optical diffraction grating. |