High-sensitivity detection of narrowband light in a more intense broadband background using coherence interferogram phase

This paper describes an optical interferometric detection technique,. known as the interferogram phase step shift, which detects narrowband, coherent, and partially coherent light in more intense broadband incoherent background light using changes in the phase gradient with the optical path difference of the coherence interferograin to distinguish the bandwidth or coherence of the signal from that of the background. The detection sensitivity is assessed experimentally by measuring the smallest signal-to-background ratio or signal-to-clutter ratio (SCR), which causes a detectable change in the self-coherence interferograin phase. This minimum detectable SCR (MDSCR) is measured for the multimode He-Ne laser, resonant-cavity light-emitting diode (LED), narrowband-filtered white light, and LED signal sources in a more intense tungsten-halogen-lamp white-light background. The highest MDSCRs to date, to the authors' knowledge, are -46.42 dB for coherent light and -31.96 dB for partially coherent light, which exceed those of existing automatic single-domain techniques by 18.97 and 4.51 dB with system input dynamic ranges of 19.24 and 11.39 dB, respectively. The sensitivity dependence on the signal-to-system bandwidth ratio and on the relative offset of their central wavelengths is also assessed, and optimum values are identified

Detection of coherent light in an incoherent background

The change in position of the self-coherence function minimum is used to detect the presence of a coherent source, rather than the change in strength of the self-coherence function at the reference path difference. The system uses both optical and digital signal processing with MATLAB algorithm. An experimental system was built in the visible band, employing a Michelson interferometer, an interference filter centered in the red, and a silicon photodetector. The results were averaged over up to 50 scans, depending on the relative visibility of the white light and laser fringes, to reduce the scan to scan variability. Amplifier gain was introduced to reduce quantization noise

Variable numerical-aperture temporal-coherence measurement of resonant-cavity LEDs

The first interferometric measurements of temporal-coherence length variation with numerical aperture (NA) are described for 650 nm, resonant-cavity light-emitting diodes (LEDs) agreeing with spectrally derived results. The interferometrically measured coherence length (22 mum to 32 mum) reduced by 37% for a 0.42 increase in NA. For a larger range of NA (0-1), this would give coherence lengths (10 mum-40 mum) lying in the gap between that of conventional LEDs (similar to5 mum) and superluminescent diodes (similar to60 mum)

Experimental spectral coexistence investigation for cognitive radar

Cognitive radar offers the prospect of improved performance, or alternatively, the maintenance of existing performance under more challenging conditions, by better utilising the resources the radar system has available to it. This benefit is derived from the active control of the degrees of freedom available to the radar, based on the history of previous behaviours and the associated performance achieved, knowledge of the mission and environment, and the current perception provided by received signals. Waveform diversity is one of the degrees of freedom open to cognitive radar systems. This paper describes an experimental investigation of the use of restricted bandwidth chirps, notched chirps and notched phase coded waveforms to enable a cognitive radar to coexist with a primary user of the RF spectrum

Prediction of Topside Electromagnetic Compatibility in Concept-Phase Ship Design

An approach for the prediction of topside electromagnetic compatibility in the concept phase of naval ship design is proposed and demonstrated. The approach was developed by utilizing the commercially available numerical computational package, Computer Simulation Technology, to assess the electromagnetic environment of a Royal Navy Type 22 Batch II Frigate. A number of the results of such an assessment were validated using measurements on a 1:50 scale copper model of the Type 22 Batch II Frigate. The approach was then applied to a new concept phase design study for a Future Patrol Ship, produced by UK Ministry of Defence's Naval Design Partnership. This work is expected to be useful in assessing the severity of topside EMI, using numerical modeling and simulations, in Concept-Phase Ship Design

Sparse Ground Penetrating Radar Acquisition: Implication for Buried Landmine Localization and Reconstruction

The effectiveness of the ground penetrating radar (GPR) imaging process and its capability of correctly reconstructing buried objects is strictly bounded to a correct acquisition strategy, both in terms of data density and regularity. In some GPR applications, such as landmine detection, these requirements may not be fulfiled due to logistical limitations and environmental obstacles. In the light of autonomous platform, possibly driven by a positioning device, the knowledge of the maximum affordable grid irregularity is essential. This experimental work, employing a data set acquired at a landmine test site, provides a demonstration that the same information content could be maintained even with a sparser data grid, compared to the commonly adopted requirements, mitigating the pressing demand for a precise samples positioning

Area-level deprivation and adiposity in children: is the relationship linear?

OBJECTIVE: It has been suggested that childhood obesity is inversely associated with deprivation, such that the prevalence is higher in more deprived groups. However, comparatively few studies actually use an area-level measure of deprivation, limiting the scope to assess trends in the association with obesity for this indicator. Furthermore, most assume a linear relationship. Therefore, the aim of this study was to investigate associations between area-level deprivation and three measures of adiposity in children: body mass index (BMI), waist circumference (WC) and waist-to-height ratio (WHtR). DESIGN: This is a cross-sectional study in which data were collected on three occasions a year apart (2005-2007). SUBJECTS: Data were available for 13,333 children, typically aged 11-12 years, from 37 schools and 542 lower super-output areas (LSOAs). MEASURES: Stature, mass and WC. Obesity was defined as a BMI and WC exceeding the 95th centile according to British reference data. WHtR exceeding 0.5 defined obesity. The Index of Multiple Deprivation affecting children (IDACI) was used to determine area-level deprivation. RESULTS: Considerable differences in the prevalence of obesity exist between the three different measures. However, for all measures of adiposity the highest probability of being classified as obese is in the middle of the IDACI range. This relationship is more marked in girls, such that the probability of being obese for girls living in areas at the two extremes of deprivation is around half that at the peak, occurring in the middle. CONCLUSION: These data confirm the high prevalence of obesity in children and suggest that the relationship between obesity and residential area-level deprivation is not linear. This is contrary to the 'deprivation theory' and questions the current understanding and interpretation of the relationship between obesity and deprivation in children. These results could help make informed decisions at the local level

Fusion of Deep Representations in Multistatic Radar Networks to Counteract the Presence of Synthetic Jamming

Micro-Doppler signatures are extremely valuable in the classification of a wide range of targets. This work investigates the effects of jamming on micro-Doppler classification performance and explores a potential deep topology enabling low bandwidth data fusion between nodes in a multistatic radar network. The topology is based on an array of three independent deep neural networks (DNNs) functioning cooperatively to achieve joint classification. In addition to this, a further DNN is trained to detect the presence of jamming and from this it attempts to remedy the degradation effects in the data fusion process. This is applied to real experimental data gathered with the multistatic radar system NetRAD, of a human operating with seven combinations of holding a rifle-like object and a heavy backpack which is slung on their shoulders. The resilience of the proposed network is tested by applying synthetic jamming signals into specific radar nodes and observing the networks’ ability to respond to these undesired effects. The results of this are compared with a traditional voting system topology, serving as a convenient baseline for this work

Hand gesture classification using 24 GHz FMCW dual polarised radar

All rights reserved. This paper evaluates the classification performance of a dual polarised on receive, 24 GHz Frequency Modulated Continuous Wave (FMCW) radar system to autonomously identify micro-Doppler signatures of unique hand gestures. We employ an Eigen subspace feature selection technique on the calculated signal subspace in order to classify each gesture. Measurements using the dual polarised radar, permitting simultaneous recording of both the co-pol and cross-pol returns, are evaluated with this processing technique and results are reported herein. Our analysis displays the challenges presented by the high variance in individuals gestures and the limited additional information the cross polarised returns have provided to the classifier. Classification performance comparisons are presented when co, cross and dual polarised data are provided to the classifier. With this technique we achieve autonomous classification performance of up to 84.6% when Eigenvalue derived features are used for classification