David W. Gough

Multiple-robot system for decentralized SLAM investigations

Technical details of laboratory based robotic system for researching decentralized Simultaneous Localization and Map building (SLAM) are provided. The main components of the system are Pioneer (ActivMedia) robots, laboratory environment for mapping, laser tracking system for testing the SLAM accuracy and a suite of SLAM software algorithms. The system is used to provide a demonstration and initial practical results of decentralized multiple-platform SLAM. The paper concludes that useful system has been set-up for researching this technology area. Further, the demonstration highlights important benefits of multiple- platform decentralized SLAM over a single platform approach. These include an increase in map accuracy, an improvement in the completeness and timeliness of the map, and an increase in platform accuracy although that platform was not extrinsically sensed. Future research areas are discussed.

Design and fabrication progress in BAe's high-complexity resistor-array IR scene projector devices

Developments are described in the design and manufacture of full 512 X 512 infra-red scene projector (IRSP) systems, as well as in a high complexity demonstrator program to realize 1024 X 1024 complexity. Design aspects include choice of drive circuit, the suspended resistor pixel design factors, the choice of busbar configurations, and the optimization of emissivity coatings. Design of the peripheral drive systems for the 512 system is outlined, and progress on manufacture reported. Development plans for the provision of suitable high complexity computer scene generation is outlined.

Demonstration of free-space optical communication link incorporating a closed-loop tracking system for mobile platforms

This paper investigates some of the issues involved in creating viable free-space optical (FSO) communication links for mobile platforms. Within the aerospace industry much of the work to-date has been theoretical, entailing very sophisticated and expensive technology. In contrast, the work here focused on adding tracking and alignment technology to commercially available FSO equipment to create a practical technology demonstrator. The technology demonstration successfully took commercial FSO units designed for fixed static links and added a tracking system. A closed-loop tracking system to sense the infrared beam and actuate pan and tilt heads was developed. The results of a series of individual tests into the viability of the tracking and control technology are reported. The developed tracking system actively tracked each end of the link and remained continuously aligned while the mobile platform travelled a random 100m route, and also while the mobile unit rotated on the spot. The tracking system was independent of the main FSO link or the vehicle, requiring no knowledge of the absolute or relative location, speed or rotation of either end of the link.

Practical application of a 1:1 mapped NUC system for IRSP arrays

The 1:1 projector:NUC sensor mapping system reported in 1999 showed that small sub-arrays of projector pixels could be corrected to a fine degree. This system has been developed to join together sub-arrays and complete the NUC operation on a whole resistor array in service. Outline detail is given of the general principle of the correction, the methods involved, covering merging of sub-arrays, strategies for dead pixels and the application of corrections in real time, together with comment on the measurement time and performance against specification.

Output accuracy and resolution limitations in resistor array infrared scene projection systems

There is a growing demand for high complexity infra-red scene projector devices with improved output accuracy and resolution. Sources of inaccuracies and limitations to resolution are discussed for both projector-alone and projector-in-simulation situations. Using experience of existing system design and performance, an attempt has been made to assign realistic percentage inaccuracy figures to the various relevant effects so that a perspective can be gained of their relative importance. Schemes for improving the accuracy and resolution performance are considered, both in terms of system techniques and array device design. A revised order of relative importance is presented to assess the residual accuracy perspective after application of practicable corrective measures. We conclude that the absolute accuracy to which a unit- under-tests collected input can be relied upon under all conditions is only 90 - 95%. However, it is essential to cater for a much finer output resolution than would be deciduate by the absolute accuracy figure, although it seems doubtful that the requirements of 12 bit resolution could be obtained except in very restricted simulation/scene conditions.

Performance characteristics of a 256 x 256 suspended resistor infrared scene generator system

A 256 X 256 suspended resistor infrared scene generator system is being constructed. The system consists of a high technology core device which generates the infrared radiation and three conventional technology peripheral subsystems. At the time of writing, measurements have been made of the critical core device component parts, i.e., the transistor drive backplane and the suspended resistor superstructure separately, measurements of the complete integrated system have yet to be completed. Measurements of performance are presented and brief subsystem descriptions are included to aid in understanding of the overall system.

Refinements in practical accuracy factors for resistor-array IR scene projectors

We describe incremental improvements in measurement, understanding and control of sensor-perceived scene accuracy factors for BAe resistor-array IR scene projector devices by means of system and device design, analysis and measurement methodology. Progress has been made in the areas of fill- factor measurement, aliasing effects, dead pixel statistics, image spreading, the design of non-uniformity correction (NUC) systems, busbar robbing, heatsink effects and noise sources.

Practical accuracy factors in resistor-array infrared scene projector systems

This is the second in a series of papers describing an on- going investigation into the detailed performance of our resistor array infra-red scene projector devices and systems. The purpose is to extract understanding and information which will enable validation of simulations involving the systems, and design compromises to be resolved. Following last years conclusions, the importance of Non Uniformity Correction is reinforced and the concept of Local Step Error and its importance is developed and investigated practically. A test methodology is developed, and the first steps in practical measurements are reported.

Developments in the use and design of a suspended resistor IR scene projector technology

This paper describes two aspects of work carried out at British Aerospace on a family of suspended resistor infrared scene generators intended as sources for exercising infrared seeker systems in simulation environments. In the first aspect, a 256 X 256 system has matured and entered service with hardware-in-the-loop (HWIL) simulation facilities. This system, designated TPS4 (for thermal picture synthesizer) has performance suitable for air target tracking studies, and certain aspects of its characteristics in use are described. In the second aspect, research work has been carried out on the extension of the system performance to enable the representation of higher temperature targets, such as are required for countermeasures work. These improved devices are designated TPS5, and aspects of their rationale, design, and evaluation are described. Prototype arrays suitable for eventual systems of complexity 512 X 512 and beyond have been tested.

Experimental study of network-centric data fusion algorithms

Network-centric architectures are defined by the complete absence of a traditional central data fusion site and also, in general, a central communication facility. Instead, the data fusion is performed at each network node and these nodes communicate on a strictly point-to-point basis. The network topology, which may be dynamic, is assumed to be unknown. These governing constraints imply a fault-tolerant, scalable, and modular system. However, such systems are prone to possible inconsistent fused estimates as a consequence of the well-known rumor propagation problem. The algorithmic challenge is to combat this problem without sacrificing the aforementioned benefits. This has led to the formulation of a technique known as Covariance Intersection (CI). Most recently, CI has been integrated with the Kalman filter to produce the Split CI algorithm - a general solution to decentralised data fusion in arbitrary communication networks. These algorithms have not yet been evaluated outside of a limited simulation environment. The purpose of this paper is to present a study of their relative performance in a hardware-based decentralised sensor network system. The paper will describe a number of indoor experiments that involve tracking a ground target by means of multiple, networked, wall-mounted cameras. High precision ground truth target positions are available from a laser-tracking device. The experiments will evaluate Kalman, CI, and Split CI algorithm performance - measured in terms of consistency, convergence and accuracy - with respect to a range of static and dynamic network topologies.