Geo Light Imaging National Testbed (GLINT) - past, present, and future

Object identification in deep space is a surveillance mission critical to our national defense. Satellite health / status monitoring is another important space surveillance task with both military and civilian applications. Deep space satellites provide challenging targets for ground-based optical sensors due to the extreme range imposed by gee-stationary and geosynchronous orbits. The Air Force Research Laboratory, in partnership with Trex Enterprises and our other contractor partners, will build a new ground-based sensor to address these deficiencies. The Geo Light imaging National Testbed (GLINT) is based on an active imaging concept known as Fourier telescopy. In this technique, the target satellite is illuminated by two or more laser sources. The corresponding fields interfere at the satellite to form interference fringes. These fringes may be made to move across the target by the introduction of a frequency shift between the laser beams. The resulting time-varying laser backscatter contains information about a Fourier component of the target reflectivity and may be collected with a large solar heliostat array. This large unphased receiver provides sufficient signal-to-noise ratio for each Fourier component using relatively low power laser sources. A third laser source allows the application of phase closure in the image reconstruction software. Phase closure removes virtually all low frequency phase distortions and guarantees that the phases of all fringes are relatively fixed. Therefore, the Fourier phase associated with each component can be recovered accurately. This paper briefly reviews the history of Fourier telescopy, the proposed design of the GLINT system, and the future of this research area.