The Lea Navigation in the north-east of London, a canalised reach of the River Lea, is affected by episodes of very low levels of dissolved oxygen. The problem was detected by the Environment Agency in the stretch from the confluence with Pymmes Brook (which receives the final effluent of Deephams sewage treatment works) to the Olympic area (Marshgate Lane, Stratford). In this project, possible causes and sources of the poor water quality in the Lea Navigation have been investigated using a multi-parameter approach. A study of physico-chemical parameters, obtained from Environment Agency automated monitoring stations, gave a clear picture of the poor river water quality at three sites in this reach. River water ecotoxicity to the freshwater alga Pseudokirchneriella subcapitata was determined by algal growth inhibition tests, following the OECD guidelines. Moreover, a novel protocol was developed which involved the use of E. coli biosensors (CellSense) operating at a lower potential than the standard protocol and using pre-concentrated river water samples. This protocol is promising and it has the potential to be a useful tool to determine the toxicity of contaminants at environmental concentrations. Furthermore, the developed protocol is a rapid, easy to perform bioassay, with potential application in achieving the aims of the Water Framework Directive (WFD). In addition to the data from the Environment Agency automatic monitoring stations and the laboratory-based tests, two in situ monitoring approaches were performed: 1) a detailed spatial seasonal monitoring of physico-chemical parameters of river water at twenty-three sites, and 2) algal growth inhibition tests, with algae entrapped in alginate beads, at seven monitoring stations. Results showed chronic pollution, and identified polar compounds in the river water and high bacterial concentrations as possible causes of low dissolved oxygen levels. This study confirmed the negative impact of Deephams STW (throughout Pymmes Brook) on the water quality of the Lea Navigation. However, there was evidence of other sources of pollution, in particular Stonebridge Brook was identified as uncontrolled source of pollution and untreated wastewater. Other possible sources include Old Moselle Brook, diffuse pollution from surface runoff, boat discharges and other undetected misconnections. Finally, in the light of the WFD, this project provides a case study on the investigation of river water quality, providing evidence that the multiparameter approach is reliable, and low cost approach for the monitoring of freshwater bodies.

International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada / The 746th Test Squadron at Holloman AFB has developed and utilized the Central Inertial Guidance Test Facility (CIGTF) High Accuracy Post-processing Reference System (CHAPS). CHAPS is a multi-sensor navigation reference system used to evaluate position, velocity, and attitude performance of Global Positioning System (GPS), Inertial Navigation System (INS), and Embedded GPS/INS (EGI) navigation systems on large vehicles and aircraft. Reference data is processed post-test with accuracy ranges from a meter to sub-meter depending on the reference configuration and test environment (profile, trajectory dynamics, GPS jamming, etc.). The GPS Aided Inertial Navigation Reference (GAINR) system developed by the Air Force Flight Test Center (Edwards AFB) offered other utilization capabilities (test beds and post-processing time). The basic sensor assembly is an EGI navigation system. The data are post-processed with Multisensor Optimal Smoothing Estimation Software (MOSES). Incorporating CHAPS and GAINR capabilities generates a reference system with enhanced accuracy (sub-meter) in a dynamic GPS non-jamming/jamming environment. This paper will present the enhanced reference system combination of CHAPS/GAINR capabilities, characterization process and development methodology.

With advancing age, many cognitive faculties deteriorate, and navigation abilities may be among those most affected. The majority of previous work investigating navigation impairments in ageing has focused on allocentric processing, attributing deficits to hippocampal dysfunction. However, real-world navigation is dependent upon numerous different strategies, as well as the ability to flexibly switch between them. Outside the context of navigation, it has been demonstrated that strategy switching, thought to be coordinated by regions of prefrontal cortex and the locus coeruleus-noradrenergic system, is also susceptible to the effects of ageing. Deficits in navigational strategy switching, and prefrontal or noradrenergic dysfunction, are therefore also likely to contribute to age-related navigation impairments. The work presented in this thesis aimed to explore age-related impairments in strategy switching within the context of navigation, and the underlying neural mechanisms in terms of a prefrontal-noradrenergic model of switching. The studies presented in Chapter Three assessed the use of allocentric and egocentric navigational strategies by young and older people. Older participants tended to use an egocentric strategy where an allocentric strategy was required, possibly due to a difficulty in switching to the appropriate allocentric strategy. In Chapter Four, I provide an account of two studies directly assessing navigational strategy switching, using two different tasks based in virtual reality. The first study utilised a virtual adaptation of the plus maze task, involving switching between an allocentric place strategy and an egocentric response strategy, and demonstrated that older participants were specifically impaired at switching to the place strategy. The second study used a more realistic task set in a virtual town environment, which involved switching from an egocentric route-following strategy to an allocentric wayfinding strategy, and also demonstrated an age-related deficit in switching to an allocentric strategy. In Chapter Five, I begin to explore the mechanisms underlying impaired navigational strategy switching in ageing. Firstly, I describe a further behavioural study that used variants of the virtual plus maze and a navigational gambling task to demonstrate a contribution of impaired decision making to the deficit in switching to an allocentric strategy. This indicates that the deficit can be attributed, at least in part, to prefrontal dysfunction. A second study presented in the same chapter demonstrated that practising orienteering does not protect against decline in navigational strategy switching ability with ageing. Chapter Six provides an account of my direct assessment of the neural bases of navigational strategy switching using functional magnetic resonance imaging. In young subjects, I found some evidence in support of the roles of prefrontal regions in navigational strategy switching. However, I was unable to complete development of a task suitable for assessing age differences in functional activation of brain regions involved in navigational strategy switching. The final experimental study, included in Chapter Seven, assessed pupil size and heart rate as physiological correlates of noradrenergic activity during performance of the virtual plus maze. Both young and old participants demonstrated a noradrenergic response to all strategy changes, suggesting that impairments are more likely attributable to dysfunction of prefrontal cortex than of the locus coeruleus, although some subtle effects suggested that noradrenergic dysfunction does have some effect on navigational strategy switching deficits. In the same chapter, I report the results of a meta-analysis of data from five of the preceding studies, suggesting that deficits in both strategy switching and allocentric processing combine to produce a greater impairment in switching to an allocentric strategy. The main finding of this series of studies is that navigational strategy switching is impaired in ageing, which may contribute to the more widely reported difficulties that older people have with navigation. My work also provides evidence in support of a prefrontal-noradrenergic model of navigational strategy switching, and suggests that dysfunction of prefrontal cortex and, to a lesser extent, the locus coeruleus-noradrenergic system is responsible for decline in navigational strategy switching ability with ageing. In conclusion, this thesis draws attention to the important role of deficient executive processing and dysfunction of extra-hippocampal brain regions in age-related navigation impairments.

International Telemetering Conference Proceedings / October 28-31, 1996 / Town and Country Hotel and Convention Center, San Diego, California / The Global Positioning System (GPS) is a very accurate, all-weather, world wide three dimensional navigation system and it has been used in almost every field related to positioning and navigation. This paper presents a new application of GPS technology - personal positioning and navigation system. It combines VP ONCORE receiver OEM (Original Equipment Manufacture) board and an intelligent system controller, with a keyboard and a programmable LCD as its peripherals. This system can realize rich navigation functions and satisfy the need of personal use.

This thesis investigates the problem of sensors used with mobile robots. Firstly, a colour sensor is considered, for its ability to detect objects having the three primary colours Red, Green and Blue (RGB). Secondly, an accelerometer was investigated, from which velocity was derived from the raw data using numerical integration. The purpose of the design and development of the sensors was to use them for robotic navigation and collision avoidance. This report presents the results of experiments carried out on the colour sensor and the accelerometer. A discussion of the results and some conclusions are also presented. It proved feasible to achieve the goal of detecting colours successfully but only for a limited distance. The accelerometer proved reliable but is not yet being applied in real time. Both the colour sensor and the accelerometer proved to be inexpensive. Some recommendations are made to improve both the colour sensor and the accelerometer sensors.

Small satellites are becoming increasingly appealing as technology advances and shrinks in both size and cost. The development time for a small satellite is also much less compared to a large satellite. For small satellites to be successful, the navigation systems must be accurate and very often they must be autonomous. For lunar navigation, contact with a ground station is not always available and the system needs to be robust. The extended Kalman filter is a nonlinear estimator that has been used on-board spacecraft for decades. The filter requires linear approximations of the state and measurement models. In the past few years, the unscented Kalman filter has become popular and has been shown to reduce estimation errors. Additionally, the Jacobian matrices do not need to be derived in the unscented Kalman filter implementation. The intent of this research is to explore the capabilities of the extended Kalman filter and the unscented Kalman filter for use as a navigation algorithm on small satellites. The filters are applied to a satellite orbiting the Moon equipped with an inertial measurement unit, a sun sensor, a star camera, and a GPS-like sensor. The position, velocity, and attitude of the spacecraft are estimated along with sensor biases for the IMU accelerometer, IMU gyroscope, sun sensor and star camera. The estimation errors are compared for the extended Kalman filter and the unscented Kalman filter for the position, velocity and attitude. The analysis confirms that both navigation algorithms provided accurate position, velocity and attitude. The IMU gyroscope bias was observable for both filters while only the IMU accelerometer bias was observable with the extended Kalman filter. The sun sensor biases and the star camera biases were unobservable. In general, the unscented Kalman filter performed better than the extended Kalman filter in providing position, velocity, and attitude estimates but requires more computation time. / text

Many mobility impaired users are unable to operate a powered wheelchair safely, without causing harm to themselves, others, and the environment. Smart wheelchairs that assist or replace user control have been developed to cater for these users, utilising systems and algorithms from autonomous robots. Despite a sustained period of research and development of robotic wheelchairs, there are very few available commercially. This thesis describes work towards developing a navigation system that is aimed at being retro-fitted to powered wheelchairs. The navigation system developed takes a systems engineering approach, integrating many existing open-source software projects to deliver a system that would otherwise not be possible in the time frame of a master's thesis. The navigation system introduced in this thesis is aimed at operating in an unstructured indoor environment, and requires no a priori information about the environment. The key components in the system are: obstacle avoidance, map building, localisation, path planning, and autonomously travelling towards a goal. The test electric wheelchair was instrumented with the following: a laptop, a laser scanner, wheel encoders, camera, and a variety of user input methods. The user interfaces that have been implemented and tested include a touch screen friendly graphical user interface, keyboard and joystick.

This thesis explores the role of path integration on the firing of hippocampal place cells and medial entorhinal grid cells. Grid cells fire at equidistant locations in an environment, indicating that they keep track of the distance and direction an animal has moved in an environment. One class of model of path integration uses a continuous attractor network to update position information. The first part of this thesis showed that such a network can generate a "look-ahead" of neural activity that sweeps through the positions just visited and about to be visited, on the short time scale that is observed<italic>in vivo</italic>. Adding intrinsic currents to the neurons in the network model allowed this look-ahead to recur every theta cycle, and generate grid fields of a size comparable to data. Grid cells are a major input the hippocampus, and are hypothesized to be the source of the place specificity of place cells. When an animal explores an open environment, place cells are active in a particular location regardless of the direction in which the animal travels through it. While performing a specific task, such as visiting specific locations in the environment in sequence, however, most place cells are active only in one direction. The second part of this thesis studied the development of this directionality. It was determined that upon the initial appearance of place fields in a novel environment, place cells fired in all directions, supporting the hypothesis that the path integration is the primary determinant of place specificity. The directionality of place fields developed gradually, possibly as a result of learning. Ideas about how this directionality could develop are explored.

This thesis deals with the challenge of autonomous navigation of the ExoMars rover. The absence of global positioning systems (GPS) in space, added to the limitations of wheel odometry makes autonomous navigation based on these two techniques - as done in the literature - an inviable solution and necessitates the use of other approaches. That, among other reasons, motivates this work to use solely visual data to solve the robot’s Egomotion problem. The homogeneity of Mars’ terrain makes the robustness of the low level image processing technique a critical requirement. In the first part of the thesis, novel solutions are presented to tackle this specific problem. Detection of robust features against illumination changes and unique matching and association of features is a sought after capability. A solution for robustness of features against illumination variation is proposed combining Harris corner detection together with moment image representation. Whereas the first provides a technique for efficient feature detection, the moment images add the necessary brightness invariance. Moreover, a bucketing strategy is used to guarantee that features are homogeneously distributed within the images. Then, the addition of local feature descriptors guarantees the unique identification of image cues. In the second part, reliable and precise motion estimation for the Mars’s robot is studied. A number of successful approaches are thoroughly analysed. Visual Simultaneous Localisation And Mapping (VSLAM) is investigated, proposing enhancements and integrating it with the robust feature methodology. Then, linear and nonlinear optimisation techniques are explored. Alternative photogrammetry reprojection concepts are tested. Lastly, data fusion techniques are proposed to deal with the integration of multiple stereo view data. Our robust visual scheme allows good feature repeatability. Because of this, dimensionality reduction of the feature data can be used without compromising the overall performance of the proposed solutions for motion estimation. Also, the developed Egomotion techniques have been extensively validated using both simulated and real data collected at ESA-ESTEC facilities. Multiple stereo view solutions for robot motion estimation are introduced, presenting interesting benefits. The obtained results prove the innovative methods presented here to be accurate and reliable approaches capable to solve the Egomotion problem in a Mars environment.

Trying to ‘learn’ the spatial layout of an environment is a common problem in certain application domains, such as military and emergency personnel training. Until recently this training was accomplished solely by providing maps and briefings of an environment. These methods, however, only provide topological (survey) knowledge of the environment, which pays little attention to the details of routes and landmarks that can only be acquired through the acquisition of procedural knowledge via navigation. Unlike previous experiments concerning spatial knowledge acquisition this work does not attempt to determine whether spatial knowledge acquisition is feasible. Such investigations have yielded a variety of results, yet all agree that spatial knowledge acquisition from a virtual environment is feasible if given enough exposure time. Accordingly, the aim of this thesis is to contribute towards a better understanding of how various individual differences and environmental factors impact the exposure time requirements needed for a person to acquire spatial knowledge from a virtual environment. Although the results of our investigation should be used with caution, we show that a one-size-fits-all situation is not possible when estimating the required exposure time that a user needs to acquire spatial knowledge. Moreover we provide a guide that allows a trainer to predict the required exposure time a person will require, by using the person's personal profile, and the environment's particular factors. In addition, we found that one of the tests we used during our investigation caused unnecessary frustration and confusion to our participants. This test is a standard way of finding a participant's orientation skill, and is commonly used in the area of spatial knowledge acquisition. Therefore, by recreating a new electronic version of the test and comparing the scores from both the new test and the old one our investigation showed that the scores on the new test were significantly higher for all participants. The training time was also lowered significantly. Our updated electronic version will be useful in future research. This test is available online at: www.newgztest.com.