Showing papers by "Neil Gordon published in 2004"

Beyond the Kalman Filter: Particle Filters for Tracking Applications

Abstract: Part I Theoretical concepts: introduction suboptimal nonlinear filters a tutorial on particle filters Cramer-Rao bounds for nonlinear filtering Part II Tracking applications: tracking a ballistic object bearings-only tracking range-only tracking bistatic radar tracking tracking targets through blind Doppler terrain aided tracking detection and tracking of stealthy targets group and extended object tracking

Bearings-only tracking of manoeuvring targets using particle filters

Abstract: We investigate the problem of bearings-only tracking of manoeuvring targets using particle filters (PFs). Three different (PFs) are proposed for this problem which is formulated as a multiple model tracking problem in a jump Markov system (JMS) framework. The proposed filters are (i) multiple model PF (MMPF), (ii) auxiliary MMPF (AUX-MMPF), and (iii) jump Markov system PF (JMS-PF). The performance of these filters is compared with that of standard interacting multiple model (IMM)-based trackers such as IMM-EKF and IMM-UKF for three separate cases: (i) single-sensor case, (ii) multisensor case, and (iii) tracking with hard constraints. A conservative CRLB applicable for this problem is also derived and compared with the RMS error performance of the filters. The results confirm the superiority of the PFs for this difficult nonlinear tracking problem.

Particle-based track-before-detect in Rayleigh noise

Abstract: Track-before-detect (TBD) refers to a tracking scheme where detection of a target is not made by placing a threshold on the sensor data. Rather, the complete sensor data is used to detect and track a target in the absence of a data threshold. By using all of the sensor data a TBD algorithm can detect and track targets which have a lower signal power than could be detected by using a standard detection and tracking scheme. This paper presents an efficient particle filter TBD algorithm, which models the signal processing stages which may be found in a sensor such as radar. In this type of sensor the noise is modelled as the magnitude of a complex Gaussian process, which is Rayleigh distributed. This noise model and the model of the sensor signal processing is incorporated into the filter derivation. It is shown that in a simple simulation the algorithm can detect and track targets with a signal-to-noise ratio as low as 3dB.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Efficient Particle-Based Track-Before-Detect in Rayleigh Noise

Abstract: Standard target state estimation schemes typically use detections as their source of measurements, which are pro- duced by thresholding the output of a sensor's signal processing stage. This work exploits a track-before-detect (TBD) technique, which simultaneously detects and tracks a target without needing to threshold the sensor data. By removing the need for threshold- ing, TBD can potentially detect and track targets with a much lower signal-to-noise ratio (SNR) than conventional systems. The signal processing that is modelled in this work is designed to match that which might be found in a sensor such as radar. In these systems, the data used by a tracking filter is the magnitude of a complex spectrum. This gives rise to a signal in Rayleigh distributed noise. This paper presents a particle-based TBD fil- ter, operating on the output of this signal processing stage, which estimates the target state incorporating target existence, position, velocity and target signal strength. The main contributions of this work are the development of an efficient method of calculating the probability of target existence and the derivation of a TBD filter which operates in Rayleigh noise. It is shown through simulation that a target can be detected and tracked with an SNR as low as 3dB. The work of Boers and Driessen (4) develops a TBD al- gorithm similar in structure to Ristic but extended to con- sider multiple targets. The algorithm presented in this paper is based heavily on that of Ristic, with the main differences being that the likelihood function is modified to more ac- curately match radar signal processing and a more efficient method for calculating the probability of target existence is developed. In this work the simulated data used as the input to the tracker is a uniform grid, with intensities defined for each bin. The intensities are modelled as the magnitude of a complex spectrum, which corresponds to the output of sig- nal processing stages in operational sensors such as radar. The envelope of complex Gaussian noise is Rayleigh dis- tributed and the magnitude of a signal in complex Gaussian noise is Ricean distributed (5). These densities are properly incorporated into the likelihood function of the TBD filter. This paper introduces a TBD algorithm for processing data with an efficient method for calculating the probability of target existence. The algorithm simultaneously estim- ates target parameters including existence, position, velo- city and signal intensity. Section 2 sets the problem math- ematically, with a summary of the models used for target motion and the assumed signal processing model. Section 3 derives the filter, incorporating target existence, while Sec- tion 4 details the implementation of this filter using sequen- tial Monte-Carlo techniques. Section 5 gives details of the simulation used to test the filter and shows results gained from repeated simulation. The final section summarises the key contributions of this paper and offers further opportun- ities for research.

High-performance long-wavelength HgCdTe infrared detectors grownon silicon substrates

Abstract: Long-wavelength HgCdTe heterostructures on silicon (100) substrates have been grown using metal-organic vapor phase epitaxy. Test diodes have been fabricated from this material using mesa technology and flip-chip bonding. We have demonstrated excellent resistance-area product characteristics for diodes with a 10.2μm cutoff wavelength. R0A values approaching 103Ωcm2 at 80K have been measured and the resistance-area product maintained above 102Ωcm2 at 1V reverse bias. Variable temperature R0A values correspond to expected generation-recombination loss mechanisms between 60 and 120K. Current-voltage characteristics of two diodes at opposite sides of an array indicate that a very uniform imaging long-wavelength infrared array could be fabricated from this material.

Multipath track association for over-the-horizon radar using Lagrangian relaxation

Abstract: Over-the-horizon radar (OTHR) uses the refraction of high frequency radiation through the ionosphere in order to detect targets beyond the line-of-sight horizon. The complexities of the ionosphere can produce multipath propagation, which may result in multiple resolved detections for a single target. When there are multipath detections, an OTHR tracker will produce several spatially separated tracks for each target. Information conveying the state of the ionosphere is required in order to determine the true location of the target and is available in the form of a set of possible propagation paths, and a transformation from measured coordinates into ground coordinates for each path. Since there is no a-priori information as to how many targets are in the surveillance region, or which propagation path gave rise to which track, there is a joint target and propagation path association ambiguity which must be resolved using the available track and ionospheric information. The multipath track association problem has traditionally been solved using a multiple hypothesis technique, but a shortcoming of this method is that the number of possible association hypotheses increases exponentially with both the number of tracks and the number of possible propagation paths. This paper proposes an algorithm based on a combinatorial optimisation method to solve the multipath track association problem. The association is formulated as a two-dimensional assignment problem with additional constraints. The problem is then solved using Lagrangian relaxation, which is a technique familiar in the tracking literature for the multidimensional assignment problem arising in data association. It is argued that due to a fundamental property of relaxations convergence cannot be guaranteed for this problem. However, results show that a multipath track-to-track association algorithm based on Lagrangian relaxation, when compared with an exact algorithm, provides a large reduction in computational effort, without significantly degrading association accuracy.

Long-wavelength infrared focal plane arrays fabricated from HgCdTe grown on silicon substrates

Abstract: We have demonstrated the successful growth of mercury cadmium telluride (MCT) infrared detector material on silicon substrates. Growth on silicon increases the maximum achievable array size, reduces manufacturing costs, and paves the way for infrared detector growth directly on multiplexing circuits. In addition, the thermal match with multiplexing circuits eliminates the requirement for complex thinning procedures. Since the crystal lattice of MCT is not matched to that of silicon, an intermediate buffer layer is required. We have developed a buffer layer technique that is compatible with MCT grown by Metal Organic Vapour Phase Epitaxy (MOVPE). Long-wavelength heterostructure device designs were grown using this technique. Test devices and 128x128 focal plane arrays were fabricated by wet etching mesa structures and passivating the mesa side-walls with a thin layer of CdTe. An indium flip-chip technique was used to form interconnects between the detector material and test or multiplexing circuit. At 77K, 50x50μm test devices with a 10.2μm cut off wavelength have been measured with R0A~1x103Ohm cm2 at zero bias and R.A~1x104Ohm cm2 at 0.1V reverse bias. Arrays from this material have been demonstrated with operabilities up to 99.7%.

Infrared negative luminescent devices and higher operating temperature detectors

Abstract: Infrared LEDs and negative luminescent devices, where less light is emitted than in equilibrium, have been attracting an increasing amount of interest recently. They have a variety of applications, including as a ‘source’ of IR radiation for gas sensing; radiation shielding for, and non-uniformity correction of, high sensitivity staring infrared detectors; and dynamic infrared scene projection. Similarly, infrared (IR) detectors are used in arrays for thermal imaging and, discretely, in applications such as gas sensing. Multi-layer heterostructure epitaxy enables the growth of both types of device using designs in which the electronic processes can be precisely controlled and techniques such as carrier exclusion and extraction can be implemented. This enables detectors to be made which offer good performance at higher than normal operating temperatures, and efficient negative luminescent devices to be made which simulate a range of effective temperatures whilst operating uncooled. In both cases, however, additional performance benefits can be achieved by integrating optical concentrators around the diodes to reduce the volume of semiconductor material, and so minimise the thermally activated generation-recombination processes which compete with radiative mechanisms. The integrated concentrators are in the form of Winston cones, which can be formed using an iterative dry etch process involving methane/hydrogen and oxygen. We present results on negative luminescence in the mid- and long-IR wavebands, from devices made from indium antimonide and mercury cadmium telluride, where the aim is sizes greater than 1 cm ×1 cm . We also discuss progress on, and the potential for, operating temperature and/or sensitivity improvement of detectors, where very high-performance imaging is anticipated from systems which require no mechanical cooling.

Higher-operating-temperature high-performance infrared focal plane arrays

Abstract: We present results from indium antimonide and mercury cadmium telluride IR detector arrays operating at temperatures above 80K, whilst retaining high performance. Multi-layer epitaxial growth is employed to minimize thermally generated leakage currents, through the use of structures designed to control transport of charge generated outside of the active region to the diode junction and to minimize Auger generation within the active region. This enables an increase in operating temperature of a few tens of degrees in the case of background limited III-V devices, and thermoelectric operation of MCT detectors sensitive to the MWIR band. We also discuss the effects of reverse bias on diodes to actively suppress the Auger generation, and the consequent introduction of 1/f noise. Optical concentrators can be used to minimize the volume of detector material in order to gain further increases in temperature. The concentrators, based on Winston cone designs, are fabricated at each pixel by reactive ion etching directly into the detector material and its substrate, and allow a theoretical reduction in volume of a factor of up to 16. This translates into a potential additional increase in temperature of several tens of degrees.

Investigations into the source of 1/f noise in HgxCd1−xTe diodes

Abstract: This work is aimed at elucidating the mechanism of 1/f noise in HgxCd1−xTe diodes in order to reduce 1/f noise in high-performance thermal cameras. Currently, to reach the required signal-to-noise ratio, the operating temperature of thermal cameras is 77 K. If 1/f noise could be reduced, this operating temperature could be raised without reducing the signal-to-noise ratio, allowing cheaper, smaller, and lighter cooling systems to be used. There are still some fundamental aspects of 1/f noise that are not fully understood. One aspect in particular is whether the noise is caused by mobility or number density fluctuations because both could give the conductivity fluctuations observed. This paper explores the noise coupling and current coupling between diodes on an array. It is shown that 1/f noise is present on the photons emitted from a forward-biased diode, suggesting that the rate of radiative recombination fluctuates. The results suggest that these fluctuations are due to carrier number-density fluctuations. From correlation measurements, it is shown that at least 32% of the 1/f noise in the forward-biased diode is correlated with carrier density fluctuations in HgxCd1−xTe diodes.

Tracking maneuvering targets using a scale mixture of normals

Abstract: The assumption of Gaussian noise in the system and measurement model has been standard practice for target tracking algorithm development for many years. For problems involving manoeuvring targets this is known to be an over-simplification and a potentially poor approximation. In this paper the use of heavy-tailed distributions is suggested as a means of efficiently modelling the behaviour of manoeuvring targets with a single dynamic model. We exploit the fact that all heavy-tailed distributions can be written as scale mixture of Normals to propose a Rao-Blackwellised particle filter (SMNPF) where particles sample the history of the continuous scale parameter and a Kalman filter is used to conduct the associated filtering for each particle. Schemes are proposed for making the proposal of new particles efficient. Performance of a heavy-tailed system model implemented via the SMNPF filter is compared against an IMM for a sample trajectory taken from a benchmark problem.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

High-performance 2D MWIR Hg 1-x Cd x Te array operating at 220K

Abstract: Infrared detectors based on Hg 1-x Cd x Te and grown by the MOVPE process can be designed to have very low dark currents, even for temperatures above 200K. These low dark currents are compatible with achieving background-limited performance at a temperature of 200K in f/2. However, in practice the detectors suffer from high 1/f noise. In this paper, a novel approach is explored in which most of the low frequency noise can be eliminated by operating the arrays at near zero bias. Using this technique, imaging arrays have been demonstrated at temperatures up to 220K giving a NETD of around 60mK in f/2.

Electron spin lifetimes in Hg0.78Cd0.22 Te and InSb

Abstract: We have made direct pump-probe measurements of spin lifetimes in long wavelength narrow-gap semiconductors at wavelengths between 4 and 10 μm and from 4 to 300 K. In particular, we measure remarkably long spin lifetimes, τ s ∼300 ps, even at 300 K for epilayers of degenerate n-type InSb. In this material the mobility is approximately constant between 77 and 300 K, and we find that τ s is approximately constant in this temperature range. In order to determine the dominant spin relaxation mechanism we have investigated the temperature dependence of τ s in non-degenerate lightly n-type Hg 0 . 7 8 Cd 0 . 2 2 Te of approximately the same band gap as InSb, and find that τ s varies from 356 ps at 150 K to 24 ps at 300 K. Our results, both in magnitude and temperature dependence of Ts, imply that the Elliott-Yafet model dominates in these materials.

Infrared negative luminescent devices and higher operating temperature detectors

Abstract: Infrared LEDs and negative luminescent devices, where less light is emitted than in equilibrium, have been attracting an increasing amount of interest recently. They have a variety of applications, including as a 'source’ of IR radiation for gas sensing; radiation shielding for and non-uniformity correction of high sensitivity starring infrared detectors; and dynamic infrared scene projection. Similarly, IR detectors are used in arrays for thermal imaging and, discretely, in applications such as gas sensing. Multi-layer heterostructure epitaxy enables the growth of both types of device using designs in which the electronic processes can be precisely controlled and techniques such as carrier exclusion and extraction can be implemented. This enables detectors to be made which offer good performance at higher than normal operating temperatures, and efficient negative luminescent devices to be made which simulate a range of effective temperatures whilst operating uncooled. In both cases, however, additional performance benefits can be achieved by integrating optical concentrators around the diodes to reduce the volume of semiconductor material, and so minimise the thermally activated generation-recombination processes which compete with radiative mechanisms. The integrated concentrators are in the form of Winston cones, which can be formed using an iterative dry etch process involving methane/hydrogen and oxygen. We will present results on negative luminescence in the mid and long IR wavebands, from devices made from indium antimonide and mercury cadmium telluride, where the aim is sizes greater than 1cm x 1cm. We will also discuss progress on, and the potential for, operating temperature and/or sensitivity improvement of detectors, where very higher performance imaging is anticipated from systems which require no mechanical cooling.