Proc. SPIE. 7323, Laser Radar Technology and Applications XIV
KEYWORDS: Signal to noise ratio, Optical imaging, Optical transfer functions, Point spread functions, Imaging systems, Spatial frequencies, Signal attenuation, Image resolution, Numerical simulations, Modulation transfer functions
Sparse aperture imaging systems are capable of producing high resolution images while maintaining an overall light
collection area that is small with respect to a fully filled aperture yielding the same resolution. However, conventional
sparse aperture systems pay the penalty of reduced contrast at
mid-band spatial frequencies.
The modulation transfer function (MTF), or normalized autocorrelation, provides a quantative measure of both the
resolution and contrast of an optical imaging system. Numerical MTF calculations were thus used to examine mid-band
contrast recovery through the systematic increase of autocorrelation redundancy in a Golay-9 sparse array.
In a Golay-9 sparse aperture arrangement, three sets of three
sub-apertures can be shown to lie at unique radii from the
center of the array. In order to increase the mid-frequency contrast we then have two options. The first, and most
influential, is to increase the size of the sub-apertures located at the intermediate radius from the array origin. This
directly increases autocorrelation redundancy at mid-band frequencies. The second option, though less effective, is to
increase the relative mid-band frequency response by attenuating the outer most sub-apertures.
We will demonstrate that by increasing the diameters of the mid-radii sub-apertures, mid-band contrast can be increased
by over 45%, compared to uniform sub-aperture diameter arrays. We will also demonstrate that attenuating the outer
most sub-apertures can further increase mid-band contrast recovery, but only by less than 1%. The effects on array fill
factor will also be discussed.