We describe our Innovative Multi Aperture Gimbaless Electro-Optical (IMAGE) testbed which uses coherent detection
of the complex field reflected off a diffuse target with seven hexagonally arranged apertures. The seven measured
optical fields are then phased with a digital optimization algorithm to synthesize a composite image whose angular
resolution exceeds that of a single aperture. This same post-detection phasing algorithm also corrects aberrations
induced by imperfect optics and a turbulent atmospheric path. We present the coherent imaging sub-aperture design
used in the IMAGE array as well as the design of a compact range used to perform scaled tests of the IMAGE array. We
present some experimental results of imaging diffuse targets in the compact range with two phase screens which
simulates a ~7[Km] propagation path through distributed atmospheric turbulence.
Developments in imaging technology for aircraft-based systems are moving in the direction of sparse, dis-
tributed aperture arrays which are conformal to the shape of the air vehicle. These modular arrays can provide
resolution capabilities similar to large monolithic telescope apertures without the associated weight and required
aircraft structural modications. A key challenge of such a system is to accomplish the imaging function without
requiring an elaborate optical relay system to bring the receive channels together on a single focal plane array
(FPA). To overcome this challenge, phased array imaging systems rely on coherent imaging through holographic
detection of the complex optical eld such as spatial-heterodyne imaging, which requires a digital processor to
synthesize the combined imagery. This approach also allows atmospheric compensation to be included digitally
in the image synthesis processing thereby eliminating any latencies due to phase modulation hardware in the
subaperture module. To support testing of phased array imaging systems, we have constructed a GPU-based
image processor capable of real-time (1 kHz) image synthesis including low-order atmospheric compensation.
Using this processor and the IMAGE testbed at UD/LOCI, we demonstrate the eectiveness of our processor
and phasing algorithm during scaled testing of a Hex-7 aperture array. We show image synthesis and compensa-
tion results from laboratory testing where atmospheric turbulence eects have been induced with phase wheels
at varying positions along the propagation path.
We present and analyze experimental results of lab-based open-loop turbulence simulation utilizing the Adaptive Aberrating Phase Screen Interface developed by ATK Mission Research, which incorporates a 2-D spatial light modulator manufactured by Boulder Nonlinear Systems. These simulations demonstrate the effectiveness of a SLM to simulate various atmospheric turbulence scenarios in a laboratory setting without altering the optical setup. This effectiveness is shown using several figures of merit including: long-term Strehl ratio, time-dependant mean-tilt analysis, and beam break-up geometry. The scenarios examined here range from relatively weak (<i>D/r<sub>o</sub></i> = 0.167) to quite strong (<i>D/r<sub>o</sub></i> = 10) turbulence effects modeled using a single phase-screen placed at the pupil of a Fourier Transforming lens. While very strong turbulence scenarios result long-term Strehl ratios higher than expected, the SLM provided an accurate simulation of atmospheric effects for conventional phase-screen strengths.