77 research outputs found
An Objective Evaluation of Four SAR Image Segmentation Algorithms
Because of the large number of SAR images the Air Force generates and the dwindling number of available human analysts, automated methods must be developed. A key step towards automated SAR image analysis is image segmentation. There are many segmentation algorithms, but they have not been tested on a common set of images, and there are no standard test methods. This thesis evaluates four SAR image segmentation algorithms by running them on a common set of data and objectively comparing them to each other and to human segmentors. This objective comparison uses a multi-metric a approach with a set of master segmentations as ground truth. The metric results are compared to a Human Threshold, which defines performance of human se mentors compared to the master segmentations. Also, methods that use the multi-metrics to determine the best algorithm are developed. These methods show that of the four algorithms, Statistical Curve Evolution produces the best segmentations; however, none of the algorithms are superior to human segmentors. Thus, with the Human Threshold and Statistical Curve Evolution as benchmarks, this thesis establishes a new and practical framework for testing SAR image segmentation algorithms
Exploring scatterer anisotrophy in synthetic aperture radar via sub-aperture analysis
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2001.Includes bibliographical references (p. 189-193).Scattering from man-made objects in SAR imagery exhibits aspect and frequency dependencies which are not always well modeled by standard SAR imaging techniques based on the ideal point scattering model. This is particularly the case for highresolution wide-band and wide-aperture data where model deviations are even more pronounced. If ignored, these deviations will reduce recognition performance due to the model mismatch, but when appropriately accounted for, these deviations from the ideal point scattering model can be exploited as attributes to better distinguish scatterers and their respective targets. With this in mind, this thesis develops an efficient modeling framework based on a sub-aperture pyramid to utilize scatterer anisotropy for the purpose of target classification. Two approaches are presented to exploit scatterer anisotropy using the sub-aperture pyramid. The first is a nonparametric classifier that learns the azimuthal dependencies within an image and makes a classification decision based on the learned dependencies. The second approach is a parametric attribution of the observed anisotropy characterizing the azimuthal location and concentration of the scattering response. Working from the sub-aperture scattering model, we develop a hypothesis test to characterize anisotropy. We start with an isolated scatterer model which produces a test with an intuitive interpretation. We then address the problem of robustness to interfering scatterers by extending the model to account for neighboring scatterers which corrupt the anisotropy attribution.(cont.) The development of the anisotropy attribution culminates with an iterative attribution approach that identifies and compensates for neighboring scatterers. In the course of the development of the anisotropy attribution, we also study the relationship between scatterer phenomenology and our anisotropy attribution. This analysis reveals the information provided by the anisotropy attribution for two common sources of anisotropy. Furthermore, the analysis explicitly demonstrates the benefit of using wide-aperture data to produce more stable and more descriptive characterizations of scatterer anisotropy.y Andrew J. Kim.Ph.D
Bayesian super-resolution with application to radar target recognition
This thesis is concerned with methods to facilitate automatic target recognition using images generated from a group of associated radar systems. Target
recognition algorithms require access to a database of previously recorded or
synthesized radar images for the targets of interest, or a database of features
based on those images. However, the resolution of a new image acquired under
non-ideal conditions may not be as good as that of the images used to generate
the database. Therefore it is proposed to use super-resolution techniques to
match the resolution of new images with the resolution of database images.
A comprehensive review of the literature is given for super-resolution when
used either on its own, or in conjunction with target recognition. A new superresolution algorithm is developed that is based on numerical Markov chain
Monte Carlo Bayesian statistics. This algorithm allows uncertainty in the superresolved image to be taken into account in the target recognition process. It
is shown that the Bayesian approach improves the probability of correct target
classification over standard super-resolution techniques.
The new super-resolution algorithm is demonstrated using a simple synthetically generated data set and is compared to other similar algorithms. A variety
of effects that degrade super-resolution performance, such as defocus, are analyzed and techniques to compensate for these are presented. Performance of the
super-resolution algorithm is then tested as part of a Bayesian target recognition
framework using measured radar data
Evidence for Reduced Specific Star Formation Rates in the Centers of Massive Galaxies at z = 4
We perform the first spatially-resolved stellar population study of galaxies
in the early universe (z = 3.5 - 6.5), utilizing the Hubble Space Telescope
Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS)
imaging dataset over the GOODS-S field. We select a sample of 418 bright and
extended galaxies at z = 3.5 - 6.5 from a parent sample of ~ 8000
photometric-redshift selected galaxies from Finkelstein et al. (2015). We first
examine galaxies at 3.5< z < 4.0 using additional deep K-band survey data from
the HAWK-I UDS and GOODS Survey (HUGS) which covers the 4000A break at these
redshifts. We measure the stellar mass, star formation rate, and dust
extinction for galaxy inner and outer regions via spatially-resolved spectral
energy distribution fitting based on a Markov Chain Monte Carlo algorithm. By
comparing specific star formation rates (sSFRs) between inner and outer parts
of the galaxies we find that the majority of galaxies with the high central
mass densities show evidence for a preferentially lower sSFR in their centers
than in their outer regions, indicative of reduced sSFRs in their central
regions. We also study galaxies at z ~ 5 and 6 (here limited to high spatial
resolution in the rest-frame ultraviolet only), finding that they show sSFRs
which are generally independent of radial distance from the center of the
galaxies. This indicates that stars are formed uniformly at all radii in
massive galaxies at z ~ 5 - 6, contrary to massive galaxies at z < 4.Comment: Accepted to ApJ, 20 pages, 15 figure
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