3.4. Relación tributaria
3.4.2. Relación de igualdad o de subordinación 75
As a result of the maturation of subsystem technology—especially antenna and comput-ing capability—the class of targets of interest in air-to-ground radar has quickly evolved
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14 C H A P T E R 1 Overview: Advanced Techniques in Modern Radar
from large collections of vehicles to single large vehicles to personal conveyance to dis-mounts. Dismounts, as the name suggests, are walking or running humans. Chapter 16,
“Human Detection with Radar: Dismount Detection,” explores methods to detect and char-acterize human targets. It first develops a time-varying, human RCS model. This model approximates the target response as the superposition of the returns from the head, torso, upper and lower arms, and upper and lower legs. The Thalman model characterizes tar-get locomotion. The corresponding spectrogram of the dismount tartar-get is quite unique, exhibiting a time-varying sinusoidal Doppler response corresponding to the torso, with distinct, semiperiodic responses resulting from appendage reflections. The challenging aspect of the dismount response is that it is generally weak compared with typical ground vehicles. Moreover, the response time variation suggests that traditional approaches to pulse integration are not viable: as the energy smears over Doppler, a single Doppler hypothesis is inappropriate. On the positive side, though, the uniqueness of the dismount response is exploitable: the key is to employ model-based matched filters that search for plausible dismount returns in the collected radar measurements. Considering all possible dismount responses is a combinatorial challenge. Chapter 16 discusses practical matched filter strategies based on efficiently estimating dismount model parameters, which is ex-tensible to dictionary-based approaches, such as orthogonal matching pursuit.
Passive bistatic radar (PBR), or passive coherent radar (PCR) as it is sometimes called, involves exploiting transmitters of opportunity—such as those on cell phone towers, car-ried by satellites, and used for direct broadcast communications—and, generally, lower-cost receivers to detect moving targets or image fixed scenes. The vast improvements in digital signal processing technology serve as the enabler for PCR. Chapter 17, “Advanced Processing Methods for Passive Bistatic Radar Systems,” discusses such PBR signal pro-cessing strategies. These primary steps include beamforming the reference channel and surveillance channel, mitigating clutter and interference, match filtering the surveillance channel using waveform information in the reference channel, and then forming and thresh-olding a range-Doppler map. System performance is determined by a number of factors, including the two-dimensional cross-correlation function (viz., the ambiguity function) for the passive waveform. This topic is considered at length, along with comprehensive discussion of practical PBR processing strategies and issues.
1.5 COMMENTS
This text is generally organized by technical area, as described in Section 1.1 and sum-marized in Table 1-1, covering a number of contemporary topics. The topics primarily emphasize processing techniques that tend to serve as critical drivers in enhancing radar performance when combined with the appropriate measurement DoFs. Measurement DoFs set the physical limit on algorithm performance; the separation of target features, clut-ter response, and inclut-terference in the measurement domain is key to improved detection, estimation, and identification performance, thereby ultimately yielding better tracking ca-pability. Electronic protection expands on the idea of exploiting measurement DoFs to all aspects of the radar design to provide resilience to electronic attack.
As seen from Table 1-1, this text broadly covers the most important, current, and emerging radar techniques. In this regard, Principles of Modern Radar: Advanced Tech-niques will serve as an invaluable reference for the student and radar practitioner.
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1.6 References 15
TABLE 1-1 Summary of Text Organization by Technical Area and Chapter
Technical Area Chapters Topics
Waveforms and spectrum 2, 3, 4, 5 Advanced pulse compression, MIMO techniques, compressive sensing Synthetic aperture radar
(SAR)
6, 7, 8 Stripmap SAR, spotlight SAR,
interferometric SAR, imaging or coherent exploitation algorithms
Array processing and interference mitigation techniques
9, 10, 11, 12 Adaptive digital beamforming, space-time adaptive processing for clutter mitigation, space-time MIMO coded apertures for multimode radar, electronic protection Post-processing
considerations
13, 14, 15 Polarimetry, automatic target recognition, multitarget and multisensor tracking Emerging techniques 16, 17 Human or dismount detection and
characterization, passive bistatic radar processing methods
Each chapter ends with problem sets the interested reader may elect to solve. While a number of these may be solved in a traditional sense with pen and paper, many also require the use of MATLAB or another suitable programming language. With an emphasis on processing techniques, the best strategy to master the material herein is the hands-on approach.
1.6 REFERENCES
[1] Richards, M.A., Scheer, J.A., and Holm, W.A. (Eds.), Principles of Modern Radar: Basic Principles, SciTech Publishing, Raleigh, NC, 2010.
[2] Billingsley, J.B., Low-Angle Radar Land Clutter: Measurements and Empirical Models, William Andrew Publishing, Inc., Norwich, NY, 2002.
[3] Skolnik, M.I., Introduction to Radar Systems, 2d ed., McGraw Hill, New York, 1980.
[4] DiFranco, J.V. and Rubin, W.L., Radar Detection, Artech House, Dedham, MA, 1980.
[5] Johnson, D.H. and Dudgeon, D.E., Array Signal Processing: Concepts and Techniques, Prentice-Hall, Englewood Cliffs, NJ, 1993.
[6] Carara, W.G., Goodman, R.S., and Majewski, R.M., Spotlight Synthetic Aperture Radar:
Signal Processing Algorithms, Artech House, Dedham, MA, 1995.
[7] Sullivan, R.J., Microwave Radar: Imaging and Advanced Concepts, Artech House, Boston, MA, 2000.
[8] Melvin, W.L., Showman, G.A., and Guerci, J.R., “A Knowledge-Aided GMTI Detection Architecture,” Proceedings of the IEEE Radar Conference, April 26–29, 2004, Philadelphia, PA.
[9] Willis, N. and Griffiths, H. (Eds.), Advances in Bistatic Radar, SciTech Publishing, Raleigh, NC, 2007.
[10] Melvin, W.L., Hancock, R., Rangaswamy, M., and Parker, J., “Adaptive Distributed Radar,”
Proceedings of the International Radar Conference, October 2009, Bordeaux, France.
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[11] Nitzberg, R., Radar Signal Processing and Adaptive Systems, Artech House, Norwood, MA, 1999.
[12] Levanon, N., Radar Principles, John Wiley & Sons, New York, 1988.
[13] Melvin, W.L. and Guerci, J.R., “Knowledge-Aided Sensor Signal Processing: A New Paradigm for Radar and Other Sensors,” IEEE Transactions on Aerospace and Electronic Systems, July 2006, pp. 983–996.
[14] Melvin, W.L., “Space-Time Adaptive Processing for Radar,” to appear in Elsevier Electronic Reference in Signal, Image and Video Processing, Academic Press.
[15] Melvin, W.L. and Showman, G.A., “Knowledge-Aided, Physics-Based Signal Processing for Next-generation radar,” in Proceedings of the Asilomar Conference on Signals, Systems, Computers, November 2007, Pacific Grove, CA.