Browsing by Author "Brady, David J"

Now showing 1 - 10 of 10
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    Adaptive millimeter-wave synthetic aperture imaging for compressive sampling of sparse scenes.
    (Opt Express, 2014-06-02) Mrozack, Alex; Heimbeck, Martin; Marks, Daniel L; Richard, Jonathan; Everitt, Henry O; Brady, David J
    We apply adaptive sensing techniques to the problem of locating sparse metallic scatterers using high-resolution, frequency modulated continuous wave W-band RADAR. Using a single detector, a frequency stepped source, and a lateral translation stage, inverse synthetic aperture RADAR reconstruction techniques are used to search for one or two wire scatterers within a specified range, while an adaptive algorithm determined successive sampling locations. The two-dimensional location of each scatterer is thereby identified with sub-wavelength accuracy in as few as 1/4 the number of lateral steps required for a simple raster scan. The implications of applying this approach to more complex scattering geometries are explored in light of the various assumptions made.
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    Analytic-domain lens design with proximate ray tracing.
    (J Opt Soc Am A Opt Image Sci Vis, 2010-08-01) Zheng, Nan; Hagen, Nathan; Brady, David J
    We have developed an alternative approach to optical design which operates in the analytical domain so that an optical designer works directly with rays as analytical functions of system parameters rather than as discretely sampled polylines. This is made possible by a generalization of the proximate ray tracing technique which obtains the analytical dependence of the rays at the image surface (and ray path lengths at the exit pupil) on each system parameter. The resulting method provides an alternative direction from which to approach system optimization and supplies information which is not typically available to the system designer. In addition, we have further expanded the procedure to allow asymmetric systems and arbitrary order of approximation, and have illustrated the performance of the method through three lens design examples.
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    Coded aperture compressive temporal imaging.
    (Opt Express, 2013-05-06) Llull, Patrick; Liao, Xuejun; Yuan, Xin; Yang, Jianbo; Kittle, David; Carin, Lawrence; Sapiro, Guillermo; Brady, David J
    We use mechanical translation of a coded aperture for code division multiple access compression of video. We discuss the compressed video's temporal resolution and present experimental results for reconstructions of > 10 frames of temporal data per coded snapshot.
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    Compressive holography of diffuse objects.
    (Appl Opt, 2010-12-01) Choi, Kerkil; Horisaki, Ryoichi; Hahn, Joonku; Lim, Sehoon; Marks, Daniel L; Schulz, Timothy J; Brady, David J
    We propose an estimation-theoretic approach to the inference of an incoherent 3D scattering density from 2D scattered speckle field measurements. The object density is derived from the covariance of the speckle field. The inference is performed by a constrained optimization technique inspired by compressive sensing theory. Experimental results demonstrate and verify the performance of our estimates.
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    Compressive sensing and adaptive sampling applied to millimeter wave inverse synthetic aperture imaging
    (Optics Express, 2017-02-06) Zhu, Ruoyu; Richard, Jonathan T; Brady, David J; Marks, Daniel L; Everitt, Henry O
    © 2017 Optical Society of America.In order to improve speed and efficiency over traditional scanning methods, a Bayesian compressive sensing algorithm using adaptive spatial sampling is developed for single detector millimeter wave synthetic aperture imaging. The application of this algorithm is compared to random sampling to demonstrate that the adaptive algorithm converges faster for simple targets and generates more reliable reconstructions for complex targets.
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    Compressive video sensors using multichannel imagers.
    (Appl Opt, 2010-04-01) Shankar, Mohan; Pitsianis, Nikos P; Brady, David J
    We explore the possibilities of obtaining compression in video through modified sampling strategies using multichannel imaging systems. The redundancies in video streams are exploited through compressive sampling schemes to achieve low power and low complexity video sensors. The sampling strategies as well as the associated reconstruction algorithms are discussed. These compressive sampling schemes could be implemented in the focal plane readout hardware resulting in drastic reduction in data bandwidth and computational complexity.
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    Generalized sampling using a compound-eye imaging system for multi-dimensional object acquisition.
    (Opt Express, 2010-08-30) Horisaki, Ryoichi; Choi, Kerkil; Hahn, Joonku; Tanida, Jun; Brady, David J
    In this paper, we propose generalized sampling approaches for measuring a multi-dimensional object using a compact compound-eye imaging system called thin observation module by bound optics (TOMBO). This paper shows the proposed system model, physical examples, and simulations to verify TOMBO imaging using generalized sampling. In the system, an object is modulated and multiplied by a weight distribution with physical coding, and the coded optical signal is integrated on to a detector array. A numerical estimation algorithm employing a sparsity constraint is used for object reconstruction.
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    Identification of fluorescent beads using a coded aperture snapshot spectral imager.
    (Appl Opt, 2010-04-01) Cull, Christy Fernandez; Choi, Kerkil; Brady, David J; Oliver, Tim
    We apply a coded aperture snapshot spectral imager (CASSI) to fluorescence microscopy. CASSI records a two-dimensional (2D) spectrally filtered projection of a three-dimensional (3D) spectral data cube. We minimize a convex quadratic function with total variation (TV) constraints for data cube estimation from the 2D snapshot. We adapt the TV minimization algorithm for direct fluorescent bead identification from CASSI measurements by combining a priori knowledge of the spectra associated with each bead type. Our proposed method creates a 2D bead identity image. Simulated fluorescence CASSI measurements are used to evaluate the behavior of the algorithm. We also record real CASSI measurements of a ten bead type fluorescence scene and create a 2D bead identity map. A baseline image from filtered-array imaging system verifies CASSI's 2D bead identity map.
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    Imaging through turbulence using compressive coherence sensing.
    (Opt Lett, 2010-03-15) Wagadarikar, Ashwin A; Marks, Daniel L; Choi, Kerkil; Horisaki, Ryoichi; Brady, David J
    Previous studies have shown that the isoplanatic distortion due to turbulence and the image of a remote object may be jointly estimated from the 4D mutual intensity across an aperture. This Letter shows that decompressive inference on a 2D slice of the 4D mutual intensity, as measured by a rotational shear interferometer, is sufficient for estimation of sparse objects imaged through turbulence. The 2D slice is processed using an iterative algorithm that alternates between estimating the sparse objects and estimating the turbulence-induced phase screen. This approach may enable new systems that infer object properties through turbulence without exhaustive sampling of coherence functions.
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    Millimeter-wave compressive holography.
    (Appl Opt, 2010-07-01) Cull, Christy Fernandez; Wikner, David A; Mait, Joseph N; Mattheiss, Michael; Brady, David J
    We describe an active millimeter-wave holographic imaging system that uses compressive measurements for three-dimensional (3D) tomographic object estimation. Our system records a two-dimensional (2D) digitized Gabor hologram by translating a single pixel incoherent receiver. Two approaches for compressive measurement are undertaken: nonlinear inversion of a 2D Gabor hologram for 3D object estimation and nonlinear inversion of a randomly subsampled Gabor hologram for 3D object estimation. The object estimation algorithm minimizes a convex quadratic problem using total variation (TV) regularization for 3D object estimation. We compare object reconstructions using linear backpropagation and TV minimization, and we present simulated and experimental reconstructions from both compressive measurement strategies. In contrast with backpropagation, which estimates the 3D electromagnetic field, TV minimization estimates the 3D object that produces the field. Despite undersampling, range resolution is consistent with the extent of the 3D object band volume.