Abstract

When an object is illuminated by a laser radar, the scattered light interferes with itself and forms a speckle pattern. If the object rotates by a small angle, the entire speckle pattern that surrounds it will also rotate about the same axis and in the same direction. To a monostatic radar, this rotation appears as a translation of the speckle pattern in a direction ϕ that is perpendicular to the projected axis of rotation. Thus, small changes in an object’s viewing angle can be sensed, and its angular motion can be characterized by observing the time dependent ϕ(t). For a circularly symmetric, spinning, and precessing object, this method allows the coning half angle, angular momentum aspect angle, instantaneous radar aspect angle, and precession period to be determined. With sufficient resolution, the wobble arising from a mass imbalance can also be obtained. In cases where internal or external forces disturb the free-body motion, the resulting perturbation can be measured, so that with appropriate models, either the disturbing forces or properties of the object, such as its mass, can be estimated. We demonstrate the speckle tracking technique by placing target models in a positioning system that simulates spin and precession. The resulting speckle motion is observed with a CCD array, and ϕ(t) is extracted using either a streaking or a cross-correlation algorithm. The measured ϕ(t) is then fitted to the theoretical model, and the coning half angle and momentum aspect angles are extracted to within a fraction of a degree.

© 1991 Optical Society of America