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This thesis is concerned with determining the orientation of small Unmanned Aerial Vehicles(UAVs). To make commercial use of these aircraft in aerial surveying markets their attitude needs to be determined accurately and precisely throughout a survey flight. Traditionally inertial sensors have been used on larger aircraft to estimate both position and orientation in combination with Global Navigation Satellite Systems (GNSS). High quality inertial sensors have many downsides when used on the small UAV. They are expensive, power hungry and often heavy. Inertial sensors are vulnerable to vibration, high acceleration, high rotation rate and jerk. All of these are present on the small UAV. This thesis identifies GNSS attitude determination as a potentially suitable alternative to inertial techniques. Carrier phase GNSS attitude determination uses three or more GNSS receivers with antennas separated by a short baseline to estimate the orientation of the UAV. This technique offers low cost, high accuracy and drift-free attitude estimates. To be successfully used it requires removal of the biases present in the received GNSS signals and estimation of the integer cycle ambiguity present in the carrier phase measurement. This thesis presents and examines the state of the art techniques for removing these biases and estimating an integer cycle ambiguity using a priori measurement of the interantenna distance. In this work a novel method is developed which uses this a priori baseline measurement to validate estimates of the carrier phase ambiguities. In order to test these methods data has been gathered using low cost, commercially available GNSS receivers and antennas. This is the first work in which modern, low cost, GNSS equipment has been tested for use in attitude determination. It is found that the state of the art carrier phase GNSS attitude determination methods can provide an accurate attitude estimate for every set of measurements from the GNSS receivers. However, a real UAV flight indicates that the low cost GNSS equipment does not track the GNSS signals throughout the flight. Signal outages, cycle slips and half cycle ambiguous carrier phase measurements occur due to rapid UAV manoeuvres. Having identified this problem this work goes on to replicate and quantify it through the use of a GNSS hardware simulator. Algorithms are then devised to increase the availability of the GNSS attitude solution throughout the tracking difficulties. Complete GNSS signal tracking failures are overcome through the innovative use of kinematic and dynamic attitude models. Both types of model give an attitude solution throughout GNSS signal tracking problems without adding significant cost or weight to the system. When tracking of the GNSS carrier phase signal is possible, novel use of the carrier phase triple difference observable allows the attitude rate to be estimated even when the carrier phase measurements are half cycle ambiguous. It is shown that integer and half integer cycle slips can be removed from the measurement through the combination of the modelling and triple difference techniques. The attitude output of both modelling and triple difference methods is used to resolve half cycle ambiguities and make full use of half cycle ambiguous data where previously it could not have been used. Success rates of up to 99.6% have been achieved for half cycle ambiguity resolution. As a result precise and accurate GNSS attitude solutions are available at nearly every epoch for which a carrier phase measurement is output by the GNSS receivers. When no measurement is available the attitude solution gracefully degrades over time. This work makes reliable, accurate, low cost attitude determination possible on mini-UAVs.

Satellite-based navigation systems make it possible to determine the relative positions of points on the earth with centimetre or even millimetre level accuracy over baselines of up to several thousand kilometres. The highest possible accuracy can only be achieved if the carrier phase integer ambiguities can be resolved. In order to resolve the L1 and L2 integer ambiguities over long GPS baselines, the double difference residual ionospheric errors must be estimated for every satellite, every epoch. The resulting number of parameters is usually too large for estimation using ordinary least squares to be practical due to the time or computing resources needed for the processing. The technique currently used to efficiently estimate the parameters is known as pre-elimination. Pre-elimination divides the unknowns into parameters of interest (the coordinates and ambiguities) and nuisance parameters (the ionospheric path delays). The nuisance parameters are treated as stochastic variables and modelled as process noise, avoiding the need for them to be explicitly estimated. Whilst this approach is highly efficient, it makes assumptions about the stochastic behaviour of the residual ionospheric error that are not necessarily valid. The effectiveness of preelimination can be increased through the use of a deterministic model of the ionosphere. It is the hypothesis of this research that the ionospheric error can be more effectively estimated than is possible with pre-elimination, leading to more reliable ambiguity resolution for long baseline precise positioning. (For complete abstract open document)

It is well-known that the meaning of a word often changes depending on the context in which the word is used. Determining the appropriate interpretation for a word occurrence requires a knowledge of the range of possible meanings for that word, and consideration of those possibilities given available contextual evidence. However, there is still much to be learned about the nature of our lexical knowledge, as well as how we make use of that knowledge in the course of language comprehension. I report on a series of three experiments that explore these issues. I begin with the question of how precise our perceptions of word meaning in context really are. In Experiment 1, I present a Magnitude Estimation study in which I obtain judgments of meaning-in-context similarity over pairs of intransitive verb occur- rences, such as The kid runs / The cat runs, or The cat runs / The lane runs. I find that participants supply a large range of very specific similarity judgments, that judgments are quite consistent across participants, and that these judgments can be at least partially predicted even by simple measures of contextual properties, such as subject noun animacy and human similarity ratings over pairs of subject nouns. However, I also find that while some participants supply a great variety of ratings, many participants supply only a few unique values during the task. This suggests that some individuals are making more fine-grained judgments than others. These differences in response granularity could stem from a variety of sources. However, the offline nature of Experiment 1 does not enable direct examination of the comprehension process, but rather focuses on its end result. In Experiment 2, I present a Speed-Accuracy Tradeoff study that explores the earliest stages of meaning-in-context resolution to better understand the dynamics of the comprehension process itself. In particular, I focus on the timecourse of meaning resolution and the question of whether verbs carry context-independent default interpretations that are activated prior to semantic integration. I find, consistent with what has previously been shown for nouns, that verbs do in fact carry such a default meaning, as can be seen in early false alarms to stimuli such as The dawn broke -- Something shattered. These default meanings appear to reflect the most frequent interpretation of the verb. While these default meanings are likely an emergent effect of repeated exposure to frequent interpretations of a verb, I hypothesize that they additionally support a shallow semantic processing strategy. Recently, a growing body of work has begun to demonstrate that our language comprehension is often less than exhaustive and less than maximally accurate -- people often vary the depth of their processing. In Experiment 3, I explore changes in depth of semantic processing by making an explicit connection to research on human decision making, particularly as regards questions of strategy selection and effort- accuracy tradeoffs. I present a semantic judgment task similar to that used in Experiment 2, but incorporating design principles common in studies on decision making, such as response-contingent financial payoffs and trial-by-trial feedback on response accuracy. I show that participants' preferences for deep and shallow semantic processing strategies are predictably influenced by factors known to affect decision making in other non-linguistic domains. In lower-risk situations, participants are more likely to accept default meanings even when they are not contextually supported, such as responding "True" to stimuli such as The dawn broke -- Something shattered, even without the presence of time pressure. In Experiment 3, I additionally show that participants can adjust not only their processing strategies but also their stimulus acceptance thresholds. Stimuli were normed for truthfulness, i.e. how strongly implied (or entailed) a probe sentence was given its context sentence. Some stimuli in the task posessed an intermediate degree of truthfulness, akin to implicature, as in The log burned -- Something was dangerous (truthfulness 4.55/7). Across 3 conditions, the threshold separating "true" from "false" stimuli was moved such that stimuli such as the example just given would be evaluated differently in different conditions. Participants rapidly learned these threshold placements via feedback, indicating that their perceptions of meaning-in-context, as expressed via the range of possible conclusions that could be drawn from the verb, could vary dynamically in response to situational constraints. This learning was additionally found to occur both faster and more accurately under increased levels of risk. This thesis makes two primary contributions to the literature. First, I present evidence that our knowledge of verb meanings is at least two-layered -- we have access to a very information-rich base of event knowledge, but we also have a more schematic level of representation that is easier to access. Second, I show that these different sources of information enable different semantic processing strategies, and that moreover the choice between these strategies is dependent upon situational characteristics. I additionally argue for the more general relevance of the decision making literature to the study of language processing, and suggest future applications of this approach for work in experimental semantics and pragmatics. / text

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The objective of the proposed research is to develop a new algorithm for range and Doppler ambiguity resolution in radar detection data using L1 minimization methods for sparse signals and to investigate the properties of such techniques. This novel approach to ambiguity resolution makes use of the sparse measurement structure of the post-detection data in multiple pulse repetition frequency radars and the resulting equivalence of the computationally intractable L0 minimization and the surrogate L1 minimization methods. The ambiguity resolution problem is cast as a linear system of equations which is then solved for the unique sparse solution in the absence of errors. It is shown that the new technique successfully resolves range and Doppler ambiguities and the recovery is exact in the ideal case of no errors in the system. The behavior of the technique is then investigated in the presence of real world data errors encountered in radar measurement and detection process. Examples of such errors include blind zone effects, collisions, false alarms and missed detections. It is shown that the mathematical model consisting of a linear system of equations developed for the ideal case can be adjusted to account for data errors. Empirical results show that the L1 minimization approach also works well in the presence of errors with minor extensions to the algorithm. Several examples are presented to demonstrate the successful implementation of the new technique for range and Doppler ambiguity resolution in pulse Doppler radars.

Range and Doppler measurement of targets for medium PRF radars is handicapped by folding and blind regions. This requires use of multiple PRFs and a resolver algorithm. The aim of the thesis is to develop various algorithms for the task and estimate their performance. Four different range and Doppler resolver algorithms and a test software is developed by using Matlab &reg / GUI and their performances due to the selected radar parameters in a multi- target environment are examined.

The main objective of this dissertation is to investigate the effects of acquiring a second language (L2) at later periods of language development and native-like homonym processing in the first language (L1) from the perspective of Event-Related brain Potentials (ERP) using a cross-modal lexical decision task. To date, there is a lack of neurophysiological investigations into the effect that acquiring an L2 can have on processing strategies in the L1, and whether or not there is a precise age at which L2 exposure no longer affects native-like language processing. As such, my goal is to pinpoint this sensitive period specifically for homonym processing. To achieve this, I will present and discuss the results of two studies. The first study employs behavioural response measures using a cross-modal lexical decision task where participants simultaneously heard a sentence and made a decision to a visually-presented pseudoword or real word. The second study employs ERP measures using a novel ERP paradigm which investigates not only the main objective of this dissertation, but the second objective as well. This second objective is for this dissertation to become the first to evaluate the outcome of combining the cross-modal lexical decision task with ERPs. The behavioural and neurophysiological results for the monolingual group support the Reordered Access Model (Duffy, Morris, & Rayner, 1988) while the results for the bilingual groups do not. The results of the current studies indicate that those bilinguals who acquired French as an L2 rather than as a second native L1 show increasing divergence from monolingual native speakers in L1 homonym processing, with later acquirers exhibiting an exponentially marked divergence. This was found even though the task was carried out in English, the L1 (or one of the L1s) of all participants. The diverging performances of the bilinguals from the monolinguals were apparent in behavioural responses as well as in the amplitude, scalp distribution, and latency of ERP components, These differences were unique to each group, which supports the hypothesis that the acquisition of an L2 influences processing in the L1 (Dussias & Sagarra, 2007). Specifically, the early and late bilingual groups exhibited a marked divergence from the monolingual group as they revealed syntactic priming effects (p<.001) as well as lexical frequency effects (p<.001). They also revealed the greatest P600-like effect as they processed target words which were inappropriately- related to the priming homonyms (such as skin in Richard had a shed in the back of the garden). This suggests a heightened sensitivity to surface cues due to the L2 influencing homonym processing in the L1 (Cook, 2003; Dussias & Sagarra, 2007). Comparatively, the monolingual group revealed equal N400-like effects for lexical ambiguities overall compared to the unrelated conditions, and a context-by-frequency-interaction slowing their processing of the target word that is appropriately-related to the subordinate reading of the priming homonym, suggesting that they are not as sensitive to these same surface cues. Importantly, these results confirm that using ERPs along with a cross-modal lexical decision task is a promising paradigm to further study language processing.

The main objective of this dissertation is to investigate the effects of acquiring a second language (L2) at later periods of language development and native-like homonym processing in the first language (L1) from the perspective of Event-Related brain Potentials (ERP) using a cross-modal lexical decision task. To date, there is a lack of neurophysiological investigations into the effect that acquiring an L2 can have on processing strategies in the L1, and whether or not there is a precise age at which L2 exposure no longer affects native-like language processing. As such, my goal is to pinpoint this sensitive period specifically for homonym processing. To achieve this, I will present and discuss the results of two studies. The first study employs behavioural response measures using a cross-modal lexical decision task where participants simultaneously heard a sentence and made a decision to a visually-presented pseudoword or real word. The second study employs ERP measures using a novel ERP paradigm which investigates not only the main objective of this dissertation, but the second objective as well. This second objective is for this dissertation to become the first to evaluate the outcome of combining the cross-modal lexical decision task with ERPs. The behavioural and neurophysiological results for the monolingual group support the Reordered Access Model (Duffy, Morris, & Rayner, 1988) while the results for the bilingual groups do not. The results of the current studies indicate that those bilinguals who acquired French as an L2 rather than as a second native L1 show increasing divergence from monolingual native speakers in L1 homonym processing, with later acquirers exhibiting an exponentially marked divergence. This was found even though the task was carried out in English, the L1 (or one of the L1s) of all participants. The diverging performances of the bilinguals from the monolinguals were apparent in behavioural responses as well as in the amplitude, scalp distribution, and latency of ERP components, These differences were unique to each group, which supports the hypothesis that the acquisition of an L2 influences processing in the L1 (Dussias & Sagarra, 2007). Specifically, the early and late bilingual groups exhibited a marked divergence from the monolingual group as they revealed syntactic priming effects (p<.001) as well as lexical frequency effects (p<.001). They also revealed the greatest P600-like effect as they processed target words which were inappropriately- related to the priming homonyms (such as skin in Richard had a shed in the back of the garden). This suggests a heightened sensitivity to surface cues due to the L2 influencing homonym processing in the L1 (Cook, 2003; Dussias & Sagarra, 2007). Comparatively, the monolingual group revealed equal N400-like effects for lexical ambiguities overall compared to the unrelated conditions, and a context-by-frequency-interaction slowing their processing of the target word that is appropriately-related to the subordinate reading of the priming homonym, suggesting that they are not as sensitive to these same surface cues. Importantly, these results confirm that using ERPs along with a cross-modal lexical decision task is a promising paradigm to further study language processing.