Calendar

Current Events

3.30

Creating a Sustainable Society

3.16

Sustainable Energy Engineering

2.28

National Science Foundation Day

2.17

Reformulation-Based Approaches to Query Optimization

2.15

FREEDM Day

2.10

WEST: Cloning Data Cache Behavior using Stochastic Traces

2.09

Computer Vision and Image Analysis in the Study of Art

2.08

GSA Social

2.03

Skewed functional processes and their applications

Time-frequency Propagation Structure for Active Sonar Tracking

Abstract:

The acoustic pressure received from a moving source in a shallow underwater channel is highly variable and its structure depends critically on characteristics of the channel such as bathymetry, sound speed, and bottom properties - which are often poorly known. This has motivated the desire to identify aspects of the field structure that are invariant to small perturbations in the propagation environment. The concept of an invariance principle was introduced by Brekhovkikh several years ago to explain the spatial interference patterns resulting from the coherent addition of propagating normal modes. The waveguide invariant is a scalar parameter that has been used extensively in passive sonar to interpret features such as intensity maxima in lofargrams.

For active bistatic geometries, the transmitted broadband pulse travels between source-to-receiver and receiver-to-target, with each of these paths introducing channel multipath structure. We recently suggested that the resulting structure as observed in a spectrogram can be described in terms of an invariant time-frequency structure similar to that used in passive sonar. We demonstrated the existence of these active striation patterns with data obtained from a reverberation experiment that was conducted in the Malta Plateau. Ongoing work in this area is the use of this structure in an extended tracker formulation which augments the kinetics in the state-space representation with physics-based time-frequency structure to limit false alarms and constrain the tracker.

 This presentation will provide an overview of underwater sonar signal processing challenges and the specific physics-based approach described above.

 Bio: Dr. Lisa M. Zurk received her Bachelor’s degree in Computer Science at University of Massachusetts, Amherst in 1985, the Master’s in Electrical and Computer Engineering at Northeastern University in 1991, and her PhD in Electrical Engineering at the University of Washington in 1985. She spent four years in industry in biomedical instrumentation and another nine years at MIT Lincoln Laboratory where she conducted research in understanding the physics of electromagnetic and acoustic wave propagation through modeling and measurement in order to devise advanced, physics-based signal processing techniques. For the 2000-2001 academic year, she was on sabbatical from MIT to teach and conduct research as a visiting Fulbright Professor in the University Helsinki Math Department. In January 2005 she joined the Electrical and Computer Engineering Department at Portland State University and subsequently founded the Northwest Electromagnetics and Acoustics Research (NEAR) Laboratory, of which she is the Director.