Laboratory and field experimental demonstration of a Fourier telescopy imaging system

Fourier telescopy (FT) is an active imaging technique that is a good candidate for high resolution imaging systems that can be used to obtain satellite images out to geosynchronous target ranges. Fourier telescopy uses multiple beams that illuminate the target with a fringe pattern that sweeps across it due to frequency differences between beams. In this way the target spatial frequency components are encoded in the temporal signal that is reflected from the target. The FT receiver can then be composed of a large area "light bucket" collector, since only the integrated temporal signal is necessary to reconstruct the target image. The GEO Light Imaging National Testbed (GLINT) system was previously designed to obtain satellite images at geosynchronous ranges by using this technique. Laboratory experiments by several groups have demonstrated the validity of this technique to produce images from simulated targets. In this paper we expand upon these previous experiments to present results from both a FT laboratory and field experimental setup that simulated realistic photon noise, speckle noise, and atmospheric turbulence that will be encountered in an actual FT imaging system. To obtain the scaling for the FT experiment, we have used the GLINT system design parameters for our experimental setup. We will also discuss the phase closure process used to eliminate the random phase differences between the beams from the target spatial frequency measurements and the basic reconstruction algorithm used to produce the target image. Results will also be given that demonstrate the phase closure variance is reduced by averaging a small number of high SNR measurements together, as compared to averaging a larger number of low SNR measurements. Target reconstruction improvements obtained by "unbiasing" the average of the individual low SNR phase closure measurements will also be discussed.