Jean J. Dolne

Analysis of time-resolved data for tomographical image reconstruction of opaque phantoms and finite absorbers in diffusive media

Experimental time-resolved data was used for direct reconstruction of images of laboratory phantoms in highly scattering media. Using different time zones of the temporal profiles, computed images were calculated by solving a one-step linear perturbation equation derived from transport theory. In nearly all cases tested, high quality reconstructions were obtained even for highly undermined problems.

Cramer-Rao lower bound and object reconstruction performance evaluation for intensity interferometry

This paper addresses the fundamental performance limits of object reconstruction methods using intensity interferometry measurements. It shows examples of reconstructed objects obtained with the FIIRE (Forward-model Interferometry Image Reconstruction Estimator) code developed by Boeing for AFRL. It considers various issues when calculating the multidimensional Cramér-Rao lower bound (CRLB) when the Fisher information matrix (FIM) is singular. In particular, when comparing FIIRE performance, characterized as the root mean square difference between the estimated and pristine objects with the CRLB, we found that FIIRE performance improved as the singularity became worse, a result not expected. We found that for invertible FIM, FIIRE yielded lower root mean squared error than the square root of the CRLB (by a factor as large as 100). This may be due to various regularization constraints (positivity, support, sharpness, and smoothness) included in FIIRE, rendering it a biased estimator, as opposed to the unbiased CRLB framework used. Using the sieve technique to mitigate false high frequency content inherent in point-by-point object reconstruction methods, we also show further improved FIIRE performance on some generic objects. It is worth noting that since FIIRE is an iterative algorithm searching to arrive at an object estimate consistent with the collected data and various constraints, an initial object estimate is required. In our case, we used a completely random initial object guess consisting of a 2-D array of uniformly distributed random numbers, sometimes multiplied with a 2-D Gaussian function.

Shadow imaging of GEO satellites

Analyses show that astronomical occultation methods may be used to determine the silhouettes of satellites at geostationary distances, a result few other techniques can achieve. Specifically, an array of photon-counting detectors is positioned in the path of the target shadow from one star. Reduction of the received star intensity vs. time can yield silhouette resolution of less than a meter. In this paper, we address the critical issues of a) the limited density of useable stars, b) positioning of the detector array into the path of the shadow, and c) undoing the effects of diffraction. A conceptual design for an imaging station is presented.

Information theoretic bounds of phase diversity for diversity polynomials and noise statistics

Information theoretic bounds on the estimated Zernike coefficients for various diversity phase functions are analyzed in this paper. We will show that, in certain cases, defocus diversity may yield higher Cramer-Rao lower bound (CRLB) than some other diversity phase functions. Evaluating the performance of the phase diversity algorithm using simulated images, we find that for an extended scene and defocus diversity, the phase diversity algorithm achieves the CRLB for known objects and approaches the CRLB by about a factor of two for unknown objects.

Time..resolved imaging in dense scattering media

The ability to image at optical frequencies objects embedded in a dense scattering medium has been experimentally evaluated using a previously described Progressive Expansion (PE) algorithm. Optical backscatter measurements were performed in a limited raster-type scan using a colliding pulse modelocked (CPM) femtosecond laser operating at 620 nm and streak camera. Data were collected in the presence and absence of the embedded absorber (3 mm diameter bead) located at a depth not visible from the surface, smoothed and evaluated between - - 200 ps in steps of 36 ps, using an overlapping approach contained in the PE algorithm, which is based on a linear perturbation model. Results obtained demonstrate the sensitivity of reconstructed images to variations in source and detector locations in relation to the subsurface location of the absorber.

Wavefront Sensing, Imaging, and Image Enhancement: introduction to the feature issue

This special issue explores various technologies related to wavefront estimation, wavefront compensation for imaging and laser beam projection, and image postprocessing. It covers topics ranging from fundamental system evaluation to system design concepts using field data.

Fundamental performance bounds of phase diversity blind deconvolution algorithm for various diversity polynomials, noise statistics, and scene size

In this paper, we will present information theoretic bounds on the estimated Zernike coefficients for various diversity phase functions. We will show that, in certain cases, defocus diversity may yield higher Cramer-Rao lower bound (CRLB) than some other diversity phase functions. Evaluating the performance of the phase diversity algorithm using simulated images, we find that for an extended scene and defocus diversity, the phase diversity algorithm achieves the CRLB for known objects and approaches the CRLB by about a factor of two for unknown objects.

Optical synthetic aperture radar imaging and phase-error compensation

We present results from simulation of an Optical Synthetic Aperture radar system(OpSAR) using a wave optics propagation model. This model allows phase and amplitude errors to be introduced anywhere along the propagation path. We show the effects of uncompensated phase errors caused by atmospheric turbulence. We demonstrate azimuth phase error compensation using a sharpness metric based on entropy minization.

Front Matter: Volume 8520

This PDF file contains the front matter associated with SPIE Proceedings Volume 8520, including the Title Page, Copyright Information, Table of Contents, and the Conference Committee listing.

Front Matter: Volume 7094

This PDF file contains the front matter associated with SPIE Proceedings Volume 7094, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.