Intelligent Hearing Aid Research
Aug. 2001 – Spring 2005
Phonak Hearing Systems, Urbana-Champaign
Most of this research is confidential to Phonak LLC
Part of doctoral research, and the main subject of
postdoctoral research
Jan. 2000 - Aug. 2001
University of
Airborne lidar provides an effective method for detection and localization of underwater objects, where the transmitted laser beam can penetrate the air-water interface and illuminate the scatterers within the water column, and the optical field generated by this scattering can be collected and processed. We consider the use of lidar data collected from different observation angles of a particular water volume to image objects of interest. Interpreting the lidar returns as tomographic projections of a 3-D reflectivity field, we formulate the problem as a 3-D tomographic image reconstruction problem. For our reconstructions, we have worked with real and synthetic data sets. The real data is obtained by a prototype airborne lidar system designed by Lockheed-Sanders for the U.S. Navy. For producing synthetic data, we have developed a model and associated computer software for airborne lidar returns by using an accurate statistical model that incorporates multiple scattering and absorption in water. For our lidar return model, we have derived lidar equations for a bistatic geometry where the transmitter and receiver can be at different locations looking in different directions. The bistatic lidar equations are the generalized form of monostatic lidar equations, where the receiver is boresighted to the transmitter and is positioned at the same location with the transmitter.
About the developed software: Used for producing synthetic data and 3-D tomographic reconstructions. Written in Matlab (ver. 5.3.1 and above) under Unix at a Sun Sparc station. Some parts written in C in the form of Matlab executable (mex) files.
Journal and conference publications: [3, 4, 7, 8].
See also UIUC Lidar Imaging Group's home page.
Part of doctoral research
Fall 1998 - Jan. 2000
University of
We consider the problem of high-resolution synthetic aperture radar (SAR) imaging of a runway and environs from an aircraft approaching for landing. We show that traditional plane-wave approximation, which leads to a simple and fast inversion scheme, is not accurate enough for this scenario and that the geometry of data collection requires the incorporation of the wavefront into the processing for high-resolution. Wavenumber-domain SAR inversion methods, such as omega-k algorithm, successfully take into account the curvature of the wavefront. It has been shown for the broadside and slightly squinted cases that the omega-k method outperforms the polar-format processing. In the highly squinted case of runway imaging, due to the severe geometric distortions the omega-k algorithm shows certain aberrations depending on the accuracy of the wavenumber-domain interpolation. In this study, we investigate the feasibility of using the omega-k algorithm, for runway imaging. We characterize the aberrations that occur when the squint angle is close to 90 degrees and show that the performance of the omega-k method can be improved by increasing the accuracy of the interpolation, and that this can be done by increasing the number of temporal frequency samples of the radar spectrum. We compare the results of the omega-k algorithm with those of a more general SAR inversion method which also can model the wavefront curvature. We also provide a solution for the left-right ambiguity for the runway imaging scenario by using interferometric SAR processing.
About the developed software: Used for point target simulation and image formation using the omega-k algorithm and the general SAR inversion method. Written in C and Matlab (ver. 5.3.1 or above) using graphical user interface (GUI) and Matlab executable (mex) files.
Journal and conference publications: [1, 2, 9,
10].
Part of doctoral research
Fall 1996 - Fall 1998
We demonstrate an acoustic system for high-resolution imaging of objects
buried in soil. Primary purpose of this system is to image cultural artifacts
in order to assess the historical significance of a potential construction
site. The system incorporates a single element acoustic source transducer and a
receiver array. Experimental data collection is performed in a controlled
volume of soil, where small objects can be buried. We have developed a
mathematical model and associated computer software to simulate the signals
acquired by the actual experimental system. We also applied the
strip-mapping synthetic aperture radar (SAR) theory to this particular
problem. We have modified the conventional correlation-based strip-mapping SAR
algorithm for bistatic acoustic data collection, along with compensation for
signal attenuation. The bistatic SAR-type reconstruction algorithm,
however, suffers from shifts and smears for near-field objects, since the
employed assumption of plane-wave propagation is not accurate enough in the
near field. On the other hand, the omega-k SAR algorithm, which takes
wavefront curvature into account, can provide more accurate results for
near-field objects. We, therefore, have formulated the image reconstruction
problem for the 3-D omega-k algorithm.
About the developed software: Written in C++ under Unix at a Sun Sparc station for synthetic data simulation and image formation by using SAR-type reconstruction algorithm.
Journal and conference publications: [5, 12, 13].
Intern
Summer 1998
Schlumberger-Doll Research,
Worked on inverse problems in the evaluation of formations around boreholes. Some of the topics included in this research were array signal processing, wavelets, and robust statistics for detection and estimation.
Software: Used wavelet toolbox WaveLab written for Matlab, under Unix at a Sun Sparc station. Wrote software for simulation of synthetic data in Matlab.
Conference publication: [11].
M.S. Study
Fall 1994 - Aug. 1996
Bilkent University,
In many areas such as sonar, radar, radio-astronomy, seismology and imaging,
reception data acquired by an array of sensors are processed to obtain
information about the source locations and the characteristics of the emitted
signals. In this study, we are concerned with the direction of arrival
estimation of superimposed wide-band signals within the maximum likelihood (ML)
estimation criterion by using the Expectation Maximization (EM) algorithm which
is an iterative method for finding ML estimates. We have worked out a thorough
derivation of the EM algorithm for the case of estimating direction of arrivals
of unknown deterministic wide-band signals incident from different directions
onto a passive array. For the required signal estimation, alternative regularized
least squares estimation techniques are proposed with significant improvement
over the standard least squares techniques. Also, for the angle of arrival
estimation of a large number of signals, a tree structured EM algorithm is
proposed and compared with the conventional EM approach. Extensive simulation
results are presented for comparison of the proposed algorithms with the
current high-resolution methods of wide-band direction finding. In order to
handle efficiently the case of available parametric prior models on the
received waveforms, the required modifications are also indicated.
About the developed software: Written in C++ under Unix at a Sun Sparc station.
Used various library routines written in Fortran and incorporated into the C++
code. Also, developed a matrix library, which achieved higher execution
speeds compared to Matlab.
Journal and conference publications: [6, 14, 15,
16].
Senior project II
Spring 1994 semester
Worked in a project of European Cooperation for Scientific and Technical Research (COST) related to object based image coding for fast tansmission of video phone images with very low bit rates.
About the developed software: Written in C for object extraction from a given video sequence.
Conference publication: [17].
Senior project I
Fall 1993 semester
Worked on modeling and analysis of bird sounds for identification of bird species. The analysis was on the time-frequency distribution of the sound data. We wrote a spectrogram software in Turbo Pascal to efficiently display the time-frequency content of a given sound pattern.
Conference publication: [18].
To see a complete list of journal and conference publications, theses, reports, posters and other presentations, click here.
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