The detection and tracking of small slow moving targets by High Frequency Surface Wave radar are limited by the presence of a dominate sea clutter spectrum. The ocean surface behaves as a distributed source in contrast to targets that are point sources. It is shown that by mapping data to eigenspaces, the sea clutter level decreases due to its nondeterministic behaviour while point targets' levels remain unchanged. The high resolution (subspace-based or eigenspace) methods and frequency tracking method for slowly time varying frequencies are evaluated to suppress this sea clutter to enhance detection of weak signals. Experimental results verify the advantage of subspace-based methods over the traditional processing techniques. Conventional subspace methods can be utilized to enhance the detection, but they deteriorate dramatically in the presence of correlated sea clutter. In our thesis some adaptive sea clutter pre-filtering schemes are introduced which improve the threshold and accuracy of subsequent subspace methods. Both simulated and real ship targets are used to verify the effectiveness of our proposed method. Furthermore, we propose another novel subspace algorithm to estimate the directions of arrival of superimposed cisoidal radar echoes from far-field targets in the radar pulse domain. The improvement provided by this algorithm is based on the use of a state space model that more accurately represents the received Doppler radar array signal prior to spatial processing such as MUSIC. A 2-d (spatial and temporal) pre-filtering matrix is structured and applied to the received array signal, which is finally combined with the high-resolution (MUSIC) method for DOA estimation. Lower resolution threshold and estimation variance are achieved by this algorithm compared to conventional beam-space MUSIC and sensor-space MUSIC. A simplified theoretical resolution threshold is derived, and both the theory and simulations verify the effectiveness of our proposed algorithm. Results from an experiment using a simulated target superimposed on real HF radar sea clutter also confirm the algorithm.

Approved for public release; distribution is unlimited / Coherent Sidelobe Cancellation (CSLC) is a coherent processing technique that has the potential of reducing noise jamming through the antenna side lobes. Present CSLCs have the capability of reducing the noise jamming by 25 to 35 dB. The maximum number of side lobe jammers that can be handled by a CSLC is equal to the number of auxiliary antennas. The performance of CSLC is governed by nonlinear stochastic differential equations that are not solvable by analytic means. Therefore this thesis employs simulation techniques to solve these equations. The CSLC becomes saturated as the number of jammers in different directions exceeds the number of loops. Jammer multipath adds an additional degree of freedom for each multipath signal that has a direction different than that of the main jammer. The objective of this thesis was to determine the effect that these multipath or hot clutter signals have on a CSLC. It was found that hot clutter produced substantial degradations on single, double and triple CSLCs. The effect was most pronounced for single cancellers where multipath with a magnitude of 1% of the jamming signal reduced the cancellation ratio by 18 dB. Comparable numbers for double and triple cancellers were 11 dB. / Major, Turkish Air Force / Lieutenant Junior Grade, Turkish Navy

Up until the 1980s, conventional radar systems consisted primarily of analog circuits, which are costly to build and compatible only to a narrow band of operations. Modern digital technology offers increasing capabilities at a lower cost making it attractive for modern radar application. The Direct Digital Synthesizer (DDS) is one such example of digital technology that is now routinely found in newer radar system designs. The DDS characteristics that most attract radar-system designers are precision frequency tuning, phase offset control, and linear "chirp" capability. This study discusses the option of incorporating DDS for use in a digital pulsed and/or frequency modulated continuous wave (FMCW) radar, and examined the necessary adaptations such as up-converting baseband signals from DDS to a radar transmission frequency, viable transmit and receive waveforms and the synchronization problem relating to synchronizing the many radiating elements that could range from a few to possibly thousands.

An â opportunistic arrayâ is a new digital antenna concept where phased array elements are placed at available open areas over the entire length of the platform. The elements are self-standing transmit-receive modules that require no hardwire connections other than prime power. All synchronization signals and data are passed wirelessly between the elements and a central signal processor. An opportunistic array that is integrated into the hull or superstructure of the warship is called an â aperstructureâ . This research investigates a wireless local oscillator distribution in the laboratory, which is a necessary requirement for the coherent operation of the array elements. The research also investigates the digitization and synchronization of multiple receive modules with the local oscillator that will determine the viability of the opportunistic array. The wireless distribution of data and control signals between the digital beamformer and transmit/receive modules requires a low-loss, wideband, simple to implement transmission system that is integrated into the structure of the warship. This research investigates several transmission structures and compares their performances.

LIDAR data taken over the Elkhorn Slough in Central California are analyzed for terrain. The specific terrain element of interest is vegetation, and in particular, tree type. Data taken on April 12th, 2005, were taken over a 10 km x 20 km region which is mixed use agriculture and wetlands. Time return and intensity were obtained at ~2.5 m postings. Multi-spectral imagery from QuickBird was used from a 2002 imaging pass to guide analysis. Ground truth was combined with the orthorectified satellite imagery to determine regions of interest for areas with Eucalyptus, Scrub Oak, Live Oak, and Monterey Cyprus trees. LIDAR temporal returns could be used to distinguish regions with trees from cultivated and bare soil areas. Some tree types could be distinguished on the basis of the relationship between first/last extracted feature returns. The otherwise similar Eucalyptus and Monterey Cyprus could be distinguished by means of the intensity information from the imaging LIDAR. The combined intensity and temporal data allowed accurate distinction between the tree types, and task not otherwise practical with the satellite spectral imagery.

SAR has traditionally been performed using high-range resolution data. This thesis is a proof-of-concept that the imaging process can be performed using high-doppler resolution data. The system requires a simple continuous wave transmitter, and the signal returns are confined to a narrow band. High-doppler resolution data is collected along an isodoppler line for different perspectives of the target. This data, a sinogram, is equivalent to taking the Radon transform of the target. The Fourier transform of the sinogram from each perspective (at an angle eÌ ) gives a slice of the two-dimensional transform subtending an angle eÌ with the axis, with equally distributed points along the line. This results in a higher density of points near the centre. Some form of weighting is necessary. This weighting is part of the Filtered Backprojection algorithm to determine the Inverse Radon transform of the sinogram. The backprojection portion is a simple redistribution of data back along the original projection line. Images were modeled by delta functions to test the above algorithm. The main points noted were that the reconstructed image was a scaled version of the original image, and that the quality of the image improved when more perspectives of the target were taken.

This thesis explores the potential benefits of two, three, and four-node distributed radar networks with the potential to provide a received SNR proportional to n2 times that of a single-node system, where n is the number of nodes in the network. By plotting the Cassini curves for these distributed radar networks along with the Cassini curves of a monostatic radar system for the same level of received SNR, these benefits are graphically demonstrated. The SNR gains result in a much larger area of coverage for the distributed radar network compared to that of a power-equivalent monostatic radar. The impact of phase and pulse synchronization on a distributed radar network is also explored. By examining phase error and pulse error separately, and then examining their impact on the coverage areas of a two-node distributed radar network, the importance of synchronization to a distributed radar network is demonstrated. / US Marine Corps (USMC) author.

A ground-penetrating radar is being designed to find subterranean structures. This is difficult to do because of varying mediums. Having more bandwidth can help mitigate this problem. Because the frequency spectrum is so cluttered, one method to do this is to use non-contiguous orthogonal frequency division multiplexing (NC-OFDM) to occupy several free areas of the spectrum. An NC-OFDM waveform was designed and optimized with respect to peak-to-average-power ratio, orthogonality, spectral leakage and autocorrelation sidelobes. Techniques such as the use of a Zadoff-Chu sequence and a gap filling algorithm were implemented to do this. The waveform was tested in simulation to show that while computationally expensive, this may be a viable waveform for ground-penetrating radar.

Total lightning mapping, along with radar and NLDN cloud-to-ground lightning data, can be used to diagnose the severity of a storm. Analysis of the 13 October 2001 supercell event (Dallas-Fort Worth, Texas), some supercells of which were tornadic, shows that LDAR II lightning source heights (quartile, median, and 95th percentile heights) increased as the storms intensified. Most of the total lightning occurred where reflectivity cores extended upwards and within regions of reflectivity gradient rather than in reflectivity cores. A total lightning hole was associated with an intense, nontornadic supercell on 6 April 2003. This feature was nonexistent from all supercells analyzed during the 13 October case. During tornadogenesis, the radar and LDAR II data indicated updraft weakening. The height of the 30 dBZ radar top began to descend approximately 10 minutes (2 volume scans) before tornado touchdown in one storm. Total lightning and CG flash rates decreased by up to a factor of 5 to a minimum during an F2 tornado touchdown associated with this storm. LDAR II source heights all showed descent by 2-4 km during a 25 minute period prior to and during this tornado touchdown. This drastic trend of decreasing source heights was observed in two tornadic storms prior to and during tornado touchdown, but did not occur in non-tornadic supercells, suggesting that these parameters can be useful to forecasters. These observations agree with tornadogenesis theory that an updraft weakens and the mesocyclone can become divided (composed of both updraft and downdraft) when a storm becomes tornadic. LDAR II source density contours were comma-shaped in association with severe wind events within mesoscale convective systems (MCSs) on 13 October 2001 and 27 May 2002. This signature is similar to the radar reflectivity bow echo. Consistent relationships between severe weather, radar and lightning storm characteristics (i.e., lightning heights) were not found for cells within MCSs as was the case for supercells. Cell interactions within MCSs are believed to weaken these relationships as reflectivity and lightning from nearby storms contaminate the cells of interest. It is also more difficult to clearly define a cell within an MCS.

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, September 1990. / Thesis Advisor(s): Morgan, Michael A. Second Reader: Adler, Richard W. "September 1990." Description based on title screen viewed on December 17, 2009. DTIC Descriptor(s): Electromagnetism, target signatures, models, target recognition, waveforms, theses, electromagnetic scattering, finite difference theory, resonant frequency, echoes, resonance, recursive functions, acoustic scattering, transients, verification. DTIC Identifier(s): Radar scattering, sonar scattering, army models, program listings. Author(s) subject terms: Natural resonances; electromagnetic scattering; acoustic scattering; radar target identification; prony's method; ARMA model. Includes bibliographical references (p. 81-82). Also available in print.