SAM Research Areas

SAM processing in radar is concerned with detection and estimation problems resulting from the transmission and reception of electromagnetic waves at antenna arrays. In our group, we specialize in radars that operate under complex multipath propagation conditions. In particular, we have a lot of experience in developing multipath signal processing methods for HF over-the-horizon (OTH) radars which "bounce" signals off the ionosphere to detect and track targets at great distances. OTH radar has been around for awhile but is experiencing a resurgence of interest because of its potential for extremely wide area surveillance at a cost which is much lower than space-based systems. Our OTH radar research concerns signal processing for next-generation systems which will be able to finding smaller and/or slower targets in more challenging ionospheric conditions. Some recent publications in this area are listed below:

1.        I. Bilik, O. Kazanci, and J.L. Krolik, “Radar clutter mitigation via space-time wavefront adaptive sensing”, Proc. of the IEEE International Conf. on Acoustics, Speech, and Signal Processing, (ICASSP '08), pages 2589 – 2592 Las Vegas, NV, April 2008.

2.        O. Kazanci, I Bilik, and J. Krolik “Wavefront adaptive raymode processing for over-the-horizon HF radar clutter mitigaiton”, Proc. of IEEE Asilomar Conference on Signals, Systems, and Computers, 4 pages, Monterey, CA. November, 2007.

3.        S. Vasudevan, R. Anderson, S. Kraut, P. Gerstoft, L.T. Rogers, and J. Krolik, "Recursive Bayesian Refractivity Estimation from Radar Sea Clutter", Radio Science, Vol. 42, No. 2, RS2014, 19 pages, April 2007.

4.        D. Ramakrishnan and J.L. Krolik, “Adaptive Radar Detection in Doubly Non-Stationary Autoregressive Doppler Spread Clutter”, accepted to the IEEE Trans. on Aerospace and Electronic Systems, December 2007 (in press).

5.        R. Anderson, S. Kraut, J.L. Krolik, “Robust altitude estimation for over-the-horizon radar using a state-space multipath fading model”, IEEE Trans. on Aerospace and Electronic Systems, January, Volume: 39 , Issue 1, pp 192-201, January, 2003.

Sonar was among the first applications of sensor array processing and the complications of multipath propagation in an underwater acoustic channel continue to challenge researchers in this area. There are two types of sonar: active and passive. Active sonars intentionally radiate sound into the water and thus have similarities to radar. Passive sonars, which only listen to sounds radiated by other sources, have the advantage of covertness. In our group, we have both passive and active sonar projects. In both areas, our objective is to exploit robust phenomenology of the multipath channel to perform better detection, estimation, and classification of underwater sources and scatterers. Some recent publications in this area are listed below:

1.        R. Goldhahn, Granger Hickman, and J.L. Krolik, “Waveguide invariant?based broadband reverberation estimation and mitigation”, to appear J. of the Acoustical Society of America, November, 2008 (in press).

2.        H. Tao and J.L. Krolik, “Waveguide Invariant Focusing for Broadband Beamforming in an Oceanic Waveguide”, J. of the Acoustical Society of America, vol. 123, no. 3, pp 1338-1346, March 2008.

3.        R. Goldhahn, G. Hickman, and J. Krolik, “Waveguide invariance reverberation mitigation for active sonar”, Proc. of IEEE Conf. on Acoustics, Speech, and Signal Processing, (ICASSP '07), 4 pages Vol. ii.941 ff., Hawaii, April 2007.

4.        H. Tao and J. Krolik “Waveguide invariant focusing for broadband adaptive beamforming in a shallow water channel”. Proc. the IEEE International Conf. on Acoustics, Speech, and Signal Processing, (ICASSP '07), 4 pages Vol. ii.981 ff., Hawaii, April 2007.

5.        V. Varadarajan and J.L. Krolik, “Joint space-time interpolation for distorted linear and bistatic array geometries”, IEEE Trans. on Signal Processing, vol. 54, no. 3, pp 848-860, March 2006.

6.        V. Varadarajan and J.L. Krolik, "Array Shape Estimation and Tracking Using Active Sonar Reverberation" IEEE Trans. on Aerospace and Electronic Systems, pp. 1073-1086, July 2004.

Traditional sensor array processing is performed on platforms whose mobility and maneuverability are not directly affected by their sensor outputs. At best, a human operator may look at processed data and then advise where the platform should go next. What the platform actually does, however, is often determined by other mission tasks. With the advent of small, relatively inexpensive unmanned vehicles, this paradigm is changing. In particular, these vehicles can be completely dedicated to a sensing mission such that what they do and where they go is completely determined by what they observe. Our group is developing sensor signal processing methods that drive vehicle behavior to optimize sensing performance without an operator in the loop. This is the essence of autonomous sensing. Our projects involve both unmanned underwater and ground based vehicles. Some recent publications in this area are listed below:

1.        S. Smith, J. Krolik, and I. Bilik, “Theoretical Passive Sonar Performance of a Cluster of UUV Towed Line Arrays Employing Orientation Diversity”, Proc. IEEE OCEANS 2007, 4 pages, Vancouver, BC. Sept 2007.

2.        I. Bilik and J.L. Krolik, “Comparative Theoretical Performance of Maneuverable Unmanned Vehicles versus Conventional Towed-Arrays for Passive Sonar”, Proc. of IEEE Oceans Conference-Europe, Aberdeen, UK, 5 pages, June 2007.

3.        G. Hickman, and J.L. Krolik “Adaptive collaborative array trajectories for optimum passive detection”, Proc. of IEEE OCEANS 2006, 4 pages, Boston MA, Sept. 2006.

4.        S. Smith and J.L. Krolik “Orientation diversity for an autonomous underwater vehicle cluster”, Proc. of IEEE OCEANS 2006, 4 pages, Boston MA Sept 2006.

5.        J.L. Krolik, J. Farrell, and A. Steinhartd “ Exploiting multipath propagation for GMTI in urban environments”, Proc. of IEEE Radar Conference, 4 pages, Verona NY, April 2006.

6.        V. Varadarajan and J.L. Krolik "Target detection using dynamically reconfigurable sensor arrays", Proc. the IEEE International Conf. on Acoustics, Speech, and Signal Processing, (ICASSP '05), Volume 4, 18-23 March 2005 pg 1009-1012.

Traditionally, adaptive signal processing at the receiver has been developed quite separately from transmit signal design. While this framework works very well in many situations, it clearly fails when unwanted signals have the same spatio-temporal characteristics as the desired signal on receive. In contrast, the multiple-input-multiple-output (MIMO) techniques we are developing can perform well even when signal and clutter components are unresolved by conventional methods provided that they have different phenomology on transmit. This happens frequently in multipath propagation environments. Our work on MIMO sensing involves the development of techniques for such applications as OTH radar, urban radar, and through-the-wall sensing. Some recent publications in this area are listed below:

1.        V.F. Mecca, D. Ramakrishnan, F.C. Robey, and J.L. Krolik, “Slow-Time MIMO Space-Time Adaptive Processing”, to appear in MIMO Radar Signal Processing, Petre Stoica and Jian Li, eds., Wiley and Sons Inc. publisher, approximately 48 pages, 2008 (in press).

2.        V.F. Mecca, J.L. Krolik, and F.C. Robey, “Beamspace slow-time MIMO radar for multipath clutter mitigation”, Proc. of the IEEE International Conf. on Acoustics, Speech, and Signal Processing, (ICASSP '08), pages 2313 - 23164 Las Vegas, NV, April 2008.

3.        V.F. Mecca and J.L. Krolik, “Slow-time MIMO STAP with improved power efficiency”, Proc. of IEEE Asilomar Conference on Signals, Systems, and Computers, pages 202 - 206, Monterey, CA. November, 2007.

4.        D. Liu, J.L. Krolik, and L. Carin, “Electromagnetic Target Detection in Uncertain Media: Time Reversal and Minimum Variance Algorithms” IEEE Trans. on Geoscience and Remote Sensing, vol. 45, no. 4, pp. 934-944, April 2007.

5.        D. Liu, S. Vasudevan, J.L. Krolik, G. Bal and L. Carin, "Electromagnetic Time-Reversal Imaging in Changing Media: Experiment and Analysis", IEEE Trans. on Antennas and Propagation, vol. 55, no. 2, pp. 344-354, February 2007.

6.        V.F. Mecca, D. Ramakrishnan, and J.L. Krolik “MIMO Radar Space-Time Adaptive Processing for Multipath Clutter Mitigation”, Proc. of Fourth IEEE Workshop on Sensor Array and Multichannel Signal Processing, pp 249-253, Boston, MA, July 2006.