Showing papers by "Neil Gordon published in 2008"

Statistical analysis of motion patterns in AIS Data: Anomaly detection and motion prediction

Abstract: The paper is devoted to statistical analysis of vessel motion patterns in the ports and waterways using AIS ship self-reporting data. From the real historic AIS data we extract motion patterns which are then used to construct the corresponding motion anomaly detectors. This is carried out in the framework of adaptive kernel density estimation. The anomaly detector is then sequentially applied to the real incoming AIS data for the purpose of anomaly detection. Under the null hypothesis (no anomaly), using the historic motion pattern data, we predict the motion of vessels using the Gaussian sum tracking filter.

Adaptive coded aperture imaging in the infrared: towards a practical implementation

Abstract: An earlier paper [1] discussed the merits of adaptive coded apertures for use as lensless imaging systems in the thermal infrared and visible It was shown how diffractive (rather than the more conventional geometric) coding could be used, and that 2D intensity measurements from multiple mask patterns could be combined and decoded to yield enhanced imagery Initial experimental results in the visible band were presented Unfortunately, radiosity calculations, also presented in that paper, indicated that the signal to noise performance of systems using this approach was likely to be compromised, especially in the infrared This paper will discuss how such limitations can be overcome, and some of the tradeoffs involved Experimental results showing tracking and imaging performance of these modified, diffractive, adaptive coded aperture systems in the visible and infrared will be presented The subpixel imaging and tracking performance is compared to that of conventional imaging systems and shown to be superior System size, weight and cost calculations indicate that the coded aperture approach, employing novel photonic MOEMS micro-shutter architectures, has significant merits for a given level of performance in the MWIR when compared to more conventional imaging approaches

Performance evaluation of a wireless sensor network based tracking system

Abstract: In this paper, we present a comprehensive analysis of the performance of a wireless sensor network based target tracking system using the particle filter. In particular, we evaluate the effect of various network design parameters such as the number of nodes, number of generated particles, and sampling interval on the tracking accuracy and computation time of the tracking system. Based on our analysis, we also present recommendations on suitable values for the relevant network design parameters, which provide a reasonable tradeoff between accuracy and computational expense for this problem. In addition, we also analyse the theoretical Cramer-Rao bound as the benchmark for the best possible tracking performance. We demonstrate that the results from our simulations closely match the theoretical bounds. We also present initial results from experiments comprising of a 25 node wireless sensor network. Initial experimental results are promising and show that the PF based estimation is suitable for detection and tracking using inexpensive wireless sensor network devices.

A large area reconfigurable MOEMS microshutter array for coded aperture imaging systems

Abstract: Coded aperture imaging has been used for astronomical applications for several years. Typical implementations used a fixed mask pattern and are designed to operate in the X-Ray or gamma ray bands. Recently applications have emerged in the visible and infra red bands for low cost lens-less imaging systems and system studies have shown that considerable advantages in image resolution may accrue from the use of multiple different images of the same scene - requiring a reconfigurable mask. Previously we reported on the early feasibility of realising such a mask based on polysilicon micr-opto-electromechanical systems (MOEMS) technology and early results in the visible and near IR bands. This employs interference effects to modulate incident light - achieved by tuning a large array of asymmetric Fabry-Perot optical cavities via an applied voltage whilst a hysteretic row/column addressing scheme is used to control the state of individual elements. In this paper we present transmission results from the target mid-IR band (3-5μm), compare them with theory and describe the scale up from a 3x3 proof-of-concept MOEMS microshutter array to a 560 x 560 element array (2cm x 2cm chip) with the associated driver electronics and embedded control - including aspects of electronic design, addressing control and integration. The resultant microsystem represents a core building block to realise much larger reconfigurable masks using a tiled approach with further integration challenges in the future.

Results from the UK 3rd generation programme: Albion

Abstract: Following the development of 1 st Generation systems in the 1970s, thermal imaging has been in service with the UK armed forces for over 25 years and has proven itself to be a battle winning technology. More recently the wider accessibility to similar technologies within opposing forces has reduced the military advantage provided by these 1st Generation systems and a clear requirement has been identified by the UK MOD for thermal imaging sensors providing increased detection, recognition and identification (DRI) ranges together with a simplified logistical deployment burden and reduced through-life costs. In late 2005, the UK MOD initiated a programme known as "Albion" to develop high performance 3 rd Generation single waveband infrared detectors to meet this requirement. At the same time, under a separate programme supporting higher risk technology, a dual waveband infrared detector was also developed. The development phase of the Albion programme has now been completed and prototype detectors are now available and have been integrated into demonstration thermal imaging cameras. The Albion programme has now progressed into the second phase, incorporating both single and dual waveband devices, focussing on low rate initial production (LRIP) and qualification of the devices for military applications. All of the detectors have been fabricated using cadmium mercury telluride material (CMT), grown by metal organic vapour phase epitaxy (MOVPE) on low cost, gallium arsenide (GaAs) substrates and bump bonded to the silicon read out circuit (ROIC). This paper discusses the design features of the 3 rd Generation detectors developed in the UK together with the results obtained from the prototype devices both in the laboratory and when integrated into field deployable thermal imaging cameras.

Dual waveband MW/LW focal plane arrays grown by MOVPE on silicon substrates

Abstract: The use of silicon substrates has been very successful for producing large area focal plane arrays operating in the MWIR waveband using the MBE growth process. More recently, promising results have been obtained in the LWIR waveband using a MOVPE growth process on a buffered silicon substrate. The MOVPE growth process is also suitable for more complex multi-layer structures and we have now used this technique to produce our first MW/LW dual waveband focal plane arrays. In this paper we show that close to background limited performance can be achieved in both wavebands, however the main challenge with arrays grown on silicon is to obtain low defect counts. These first arrays are promising in this respect and operabilities of 99.4% and 98.2% have been achieved in the MWIR band and LWIR band respectively. The availability of dual waveband arrays allows the correlation of defects in the two wavebands to be compared. In general, we find that the correlation is low and this suggests that defect generation mechanisms which would affect both bands (such as threading dislocations) are currently not the main source of defective devices in MOVPE grown devices on silicon.

A high-speed, MWIR reference source for FPA non-uniformity correction using negative luminescence

Abstract: We have previously discussed the potential of using a Hg1-xCdxTe source as a reference plane for the non-uniformity correction of thermal imagers and which is being developed as an option for the UK 3 rd generation, high performance thermal imaging program (Albion). In this paper we will present our first results on a large area (1.5 cm x 1.5 cm) source which was grown on a silicon substrate and can simulate a range of temperatures from -10 o C to +30 o C. Due to the fast switching speed, the apparent temperature can be changed on a frame by frame basis. Also, the operation of the device can be synchronized to the integration time of the camera to reduce the mean power requirements by a factor of 10 and reduce thermal heating effects. The main applications for Hg1-xCdxTe devices as high-performance, cryogenically-cooled detectors typically require very low drive currents. The use of this material for large-area LEDs has generated new challenges to deal with the high peak currents. These are typically in the range 1-2 A/cm 2 for a MWIR waveband source and have led to a need to reduce the common impedance, reduce the contact resistances and consider the effects of current crowding.

Development of non-hybridised HgCdTe detectors for the next generation of astronomical instrumentation

Abstract: The superb image quality that is predicted, and even demanded, for the next generation of Extremely Large Telescopes (ELT) presents a potential crisis in terms of the sheer number of detectors that may be required. Developments in infrared technology have progressed dramatically in recent years, but a substantial reduction in the cost per pixel of these IR arrays will be necessary to permit full exploitation of the capabilities of these telescopes. Here we present an outline and progress report of an initiative to develop a new generation of astronomical grade Cadmium Mercury Telluride (HgCdTe) array detectors using a novel technique which enables direct growth of the sensor diodes onto the Read Out Integrated Circuit (ROIC). This technique removes the need to hybridise the detector material to a separate Silicon readout circuit and provides a route to very large monolithic arrays. We present preliminary growth and design simulation results for devices based on this technique, and discuss the prospects for deployment of this technology in the era of extremely large telescopes.