4,646 research outputs found
Radar: Theory and Insight
Radar principles and design considerations are reviewed, using both analytical and heuristic methods. Emphasis is placed on achieving physical insight while maintaining technical rigor. Waveform properties and signal detectability maximization through matched filtering is discussed in detail. The Moving Target Indicator radar system is presented as an illustration of digital signal processing technology applied to modern radar systems
Photonic-Doppler-Velocimetry, Paraxial-Scalar Diffraction Theory and Simulation
Author Institution: Lawrence Livermore National Laborator
Acoustic Oceanographic Buoy Test during the MREA’03 Sea Trial
Rep 04/03 - SiPLAB
10/Nov/2003Environmental inversion of acoustic signals for bottom and water column properties is
being proposed in the literature as an interesting concept for complementing direct hydrographic
and oceanographic measurements for Rapid Environmental Assessment (REA).
The acoustic contribution to REA can be cast as the result of the inversion of ocean
acoustic properties to be assimilated into ocean circulation models specifically tailored
and calibrated to the scale of the area under observation. Traditional ocean tomography
systems and methods for their requirements of long and well populated receiving
arrays and precise knowledge of the source/receiver geometries are not well adapted to
operational Acoustic REA (AREA).
An innovative concept that responds to the operational requirements of AREA is being
proposed under a Saclantcen JRP jointly submitted by the the Universit´e Libre de
Bruxelles (ULB), SiPLAB/CINTAL at University of Algarve, the Instituto Hidrogr´afico
(IH) and the Royal Netherlands Naval College (RNLNC) and approved by Saclantcen
in 2003 under the 2004 SPOW. That concept includes the development of water column
and geo-acoustic inversion methods being able to retrieve environmental true properties
from signals received on a drifting network of Acoustic-Oceanographic Buoys (AOB). A
prototype of an AOB and a preliminary version of the inversion code, was tested at sea
during the Maritime Rapid Environment Assessment’2003 sea trial (MREA’03) and is
described in this report together with the results obtained.This report presents the AOB system and the results obtained during its testing in the
MREA’03 sea trial. The MREA’03 sea trial took place off the Italian coast, near Elba I.
in the period 26 May - 27 June 2003.
The authors of this report would like to thank: the SACLANT Undersea Research Centre for the opportunity for participating in
the sea trial
• the scientist in charge Dr. Emanuel Coelho; the collaboration of Saclantcen personnel; the master and crew of the R/V Alliance; the contribution of Prof. J.-P. Hermand from ULB for the discussions and pictures
shown in this report
Pseudo-Random Codes for Single-Mode and Simultaneous Multi-Mode Operation in Ultrasonic Imaging Systems
Conventional pulse-echo imaging systems used in ultrasonics can become limited in average transmit power by transmitter, transducer, and medium peak-power limitations. In addition, imaging systems which use multi-element arrays are limited in speed by the necessity to transmit sequentially when scanning in more than one direction in order to avoid interfering echoes. A new system is studied which can overcome both the speed and power limitations by using correlation receivers and pseudo-random transmit codes. First, the performance of several single-mode correlation systems are compared to conventional pulse-echo systems in the presence of clutter and moving targets. The system which uses special pseudo-random codes called Golay codes is shown to provide the best overall performance. A multi-mode correlation system is then studied which images in many different modes (e.g. scan directions) simultaneously. This multi-mode system is studied under the effects of moving targets, clutter and background receiver noise. A comparison with the operation of Conventional sequentially-scanned phased array systems is made under a variety of signal-to-noise ratio (SNR) conditions and operating speeds to determine the optimal type of imaging system. Results indicate that under many conditions, a simultaneous multi-mode system can provide improved SNR and/or speed over conventional sequential multi-mode systems. The multi-mode system which uses Golay codes is shown to provide the best overall performanc
Turn-Key Stabilization and Digital Control of Scalable, N GTI Resonator Based Coherent Pulse Stacking Systems
Coherent Pulse Stacking Amplification (CPSA) is a new time-domain coherent addition
technique that overcomes the limitations on pulse energies achievable from optical amplifiers. It
uses reflecting resonators to transform a sequence of phase- and amplitude-modulated optical
pulses into a single output pulse enabling high pulse energy for fiber lasers.
This thesis focuses on utilizing efficient algorithms for stabilization and optimization
aspects of CPSA and developing a robust, scalable, and distributed digital control system with
firmware and software integration for algorithms, to support the CPS (Coherent Pulse Stacking)
application. We have presented the theoretical foundation of the stochastic parallel gradient
descent (SPGD) for phase stabilization, discussed its performance criteria, its convergence, and its
stability. We have presented our software and hardware development for time-domain coherent
combing stabilization (specifically, an FPGA (Field Programmable Gate Array)-based Control
system with software/firmware development to support stabilization and optimization algorithms).
Analytical formulations of output stacked pulse profile as a function of input pulse train amplitudes
and phase and stacker cavity parameters have been derived so as to build up a foundation for a
GTI (Gires-Tournois-Interferometer) Cavity-based noise measurement technique. Time-domain
and frequency domain characterization techniques have been presented to analyze phase and
amplitude noise in the stacking system. Stacking sensitivity to errors in different control
parameters (stacker cavity phase, pulse amplitude, and phases) for different stacker configurations
have been analyzed. Noise measurement results using GTI cavities with different round-trip time
has have been presented and we have shown how effectively the stacking phase noise in the system
can be reduced by improving the noise performance of the mode-locked oscillator. Simulation and
Experimental results for stabilizing different stacker configurations have been presented. Finally
an algorithmic control system along with software/hardware development for optimizing
amplitudes and phases of the input burst has been implemented to increase stacking fidelity. A
complete detailed description, and simulation of the Genetic Algorithm as an alternative algorithm
for optimizing the stacked pulse fidelity has been presented. Comparison between SPGD and
Genetic Algorithm results has been done to evaluate their performance.
To summarize, this thesis provides theoretical, experimental, and implementation aspects
of controlling CPSA system by introducing efficient control algorithms and developing a turn-key
digital control system which is scalable to large number of stacker cavities.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/147664/1/msheikhs_1.pd
Bioinspired symmetry detection on resource limited embedded platforms
This work is inspired by the vision of flying insects which enables them to detect and locate a set of relevant objects with remarkable effectiveness despite very limited
brainpower. The bioinspired approach worked out here focuses on detection of symmetric objects to be performed by resource-limited embedded platforms such as micro air vehicles. Symmetry detection is posed as a pattern matching problem which is solved by an approach based on the use of composite correlation filters. Two variants of the approach are proposed, analysed and tested in which symmetry detection is cast as 1) static and 2) dynamic pattern matching problems. In the static variant, images of objects are input to two dimentional spatial composite correlation filters. In the dynamic variant, a video (resulting from platform motion) is input to a composite correlation filter of which its peak response is used to define symmetry. In both cases, a novel method is used for designing the composite filter templates for symmetry detection. This method significantly reduces the level of detail which needs to be matched to achieve good detection performance. The resulting performance is systematically quantified using the ROC analysis; it is demonstrated that the bioinspired detection approach is better and with a lower computational cost compared to the best state-of-the-art solution hitherto available
Detection of complex point targets with distributed assets in a MIMO radar system
The report explores the problem of detecting complex point target models in a MIMO radar system. A complex point target is a mathematical and statistical model for a radar target that is not resolved in space, but exhibits varying complex reflectivity across the different bistatic view angles. The complex reflectivity can be modeled as a complex stochastic process whose index set is the set of all the bistatic view angles, and the parameters of the stochastic process follow from an analysis of a target model comprising a number of ideal point scatterers randomly located within some radius of the targets center of mass. The proposed complex point targets may be applicable to statistical inference in multistatic or MIMO radar system. Six different target models are summarized here – three 2-dimensional (Gaussian, Uniform Square, and Uniform Circle) and three 3-dimensional (Gaussian, Uniform Cube, and Uniform Sphere). They are assumed to have different distributions on the location of the point scatterers within the target. We develop data models for the received signals from such targets in the MIMO radar system with distributed assets and partially correlated signals, and consider the resulting detection problem which reduces to the familiar Gauss-Gauss detection problem. We illustrate that the target parameter and transmit signal have an influence on the detector performance through target extent and the SNR respectively. A series of the receiver operator characteristic (ROC) curves are generated to notice the impact on the detector for varying SNR. Kullback–Leibler (KL) divergence is applied to obtain the approximate mean difference between density functions the scatterers assume inside the target models to show the change in the performance of the detector with target extent of the point scatterers
Perceptual Organization
Perceiving the world of real objects seems so easy that it is difficult to grasp just how complicated it is. Not only do we need to construct the objects quickly, the objects keep changing even though we think of them as having a consistent, independent existence (Feldman, 2003). Yet, we usually get it right, there are few failures. We can perceive a tree in a blinding snowstorm, a deer bounding across a tree line, dodge a snowball, catch a baseball, detect the crack of a branch breaking in a strong windstorm amidst the rustling of trees, predict the sounds of a dripping faucet, or track a street musician strolling down the road
- …