Development and evaluation of a Kalman-filter algorithm for terminal area navigation using sensors of moderate accuracy

Translational state estimation in terminal area operations, using a set of commonly available position, air data, and acceleration sensors, is described. Kalman filtering is applied to obtain maximum estimation accuracy from the sensors but feasibility in real-time computations requires a variety of approximations and devices aimed at minimizing the required computation time with only negligible loss of accuracy. Accuracy behavior throughout the terminal area, its relation to sensor accuracy, its effect on trajectory tracking errors and control activity in an automatic flight control system, and its adequacy in terms of existing criteria for various terminal area operations are examined. The principal investigative tool is a simulation of the system

Transform processing and coding of images Final report

Transform processing and image codin

Effects of errorless learning on the acquisition of velopharyngeal movement control

Session 1pSC - Speech Communication: Cross-Linguistic Studies of Speech Sound Learning of the Languages of Hong Kong (Poster Session)The implicit motor learning literature suggests a benefit for learning if errors are minimized during practice. This study investigated whether the same principle holds for learning velopharyngeal movement control. Normal speaking participants learned to produce hypernasal speech in either an errorless learning condition (in which the possibility for errors was limited) or an errorful learning condition (in which the possibility for errors was not limited). Nasality level of the participants’ speech was measured by nasometer and reflected by nasalance scores (in %). Errorless learners practiced producing hypernasal speech with a threshold nasalance score of 10% at the beginning, which gradually increased to a threshold of 50% at the end. The same set of threshold targets were presented to errorful learners but in a reversed order. Errors were defined by the proportion of speech with a nasalance score below the threshold. The results showed that, relative to errorful learners, errorless learners displayed fewer errors (50.7% vs. 17.7%) and a higher mean nasalance score (31.3% vs. 46.7%) during the acquisition phase. Furthermore, errorless learners outperformed errorful learners in both retention and novel transfer tests. Acknowledgment: Supported by The University of Hong Kong Strategic Research Theme for Sciences of Learning © 2012 Acoustical Society of Americapublished_or_final_versio

Linear and adaptive delta modulation

New results are presented offering insight into the performance and optimization of linear and adaptive delta modulation, together with a comparison with pulse code modulation. The results are applied to three cases of practical importance: television, speech, and broadband signals. The results presented can be grouped into the following three categories. First, a performance characterization of linear delta modulation (DM) is given. With the aid of certain empirical observations made from computer simulations, closed form expressions are found for granular noise, overload noise, and minimum quantization noise powers. These results permit the prediction of the optimum performance obtainable from DM at various bandwidth expansion factor values for many classes of signals. A defined quantity called the slope loading factor is usefully employed in the characterization of DM performance. It is shown that the slope loading factor is a normalizing variable when used to describe S/NQ performance. The optimum performance of DM with signals such as television and speech having an integrated spectrum exceeds that with a broadband signal having a uniform spectrum. It was also found that DM performance obtained with a Gaussian message signal amplitude probability density is essentially the same as that obtained with an exponential density. Second, the advantages to be gained when adaptive control is introduced into the DM system are investigated. If the message signal ensemble is nonstationary, a companding function is required. It is shown that this may be provided in a DM system by forcing the step size to respond adaptively to changes in the derivative of the input signal. Adaptive DM may take either a discrete or continuous form. It is shown that discrete adaptive DM does not sacrifice optimum linear DM performance to achieve companding, and further that large values of companding improvement are possible. Because of the nonstationary nature of television and speech signals, it is concluded that adaptive DM appears better suited than linear DM to such signals. Finally, linear DM is shown to be a special case of discrete adaptive DM. Third, the noise performance of PCM with Gaussian and exponential signal densities is presented together with a comparison between DM and PCM for television, speech, and broadband message signals. It is shown that the characteristic form of the performances of PCM and DM are similar when the independent variables are the amplitude loading factor and slope loading factor respectively. The effects of logarithmic companding and signal amplitude limiting on PCM performance are investigated. It has been found that adaptive DM appears capable of realizing a larger companding improvement than PCM, and that amplitude limiting in PCM is the counterpart of slope limiting in DM. For a television signal, it is concluded that DM provides a greater maximum S/NQ performance than PCM for values of the bandwidth expansion factor less than eight. For a speech signal, it is concluded that the performance of discrete adaptive DM with a bandwidth expansion factor value of four and a final gain factor value of only eight is approximately the same as that of companded PCM with a compression parameter value of one hundred. For a broadband signal, it is concluded that the performance of PCM is superior to that of DM. Finally, because of the complex nature of television and speech communication, it is concluded that subjective tests are needed before further conclusions regarding the performance advantages of discrete adaptive DM can be reached. For an abridgment of the material in this dissertation, the reader is referred to a paper of the same title, written by the author, appearing in the Proceedings of the IEEE, March, 1967

The oceanographic and geoidal components of sea surface topography

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February, 1983Altimetric, gravimetric and oceanographic data over the North Atlantic are combined -using techniques of optimum estimation- to infer the surface expression of the time averaged circulation (ζ) and to estimate the marine geoid (γ), both in the wavelength band 100 km-2000 km. Optimum inverse methods in geophysics are reviewed. They are then used to analyze the estimation of the geoid from gravity data, emphasizing the wavenumber spectrum of resolution functions. It is found that accurate bandpassed versions of the geoid can be recovered from restricted data sets. The accuracy and distribution of publicly available gravity data are shown to define an estimate γ whose expected errors, σγ, range between 30 and 260 cm, assuming the Wagner and Colombo (1978) spectrum describes the average geoid behaviour. The σγ underestimate the actual differences between 'y and an altimetric surface (s) derived from Seasat, but the spatial variation of σγ follows closely the differences s-γ. The discrepancy is attributable to a partial failure of the spectral model at short wavelengths. The differences s-γ are dominated by geoid error that masks much of the signal ζ. The main North Atlantic gyre emerges clearly only after the σγ and the simplest model for ζ -as a spatially uncorrelated process with (30 cm)2 variance- are taken into account. To obtain a corrected geoid, a hydrographic estimate of ζ is combined with sand γ, and their expected errors.NASA's research Grant NAG6-9 funded this wor

Stellar rotational periods in the planet hosting open cluster Praesepe

By using the dense coverage of the extrasolar planet survey project HATNet, we Fourier analyze 381 high-probability members of the nearby open cluster Praesepe (Beehive/M44/NGC 2632). In addition to the detection of 10 variables (of \delta Scuti and other types), we identify 180 rotational variables (including the two known planet hosts). This sample increases the number of known rotational variables in this cluster for spectral classes earlier than M by more than a factor of three. These stars closely follow a color/magnitude -- period relation from early F to late K stars. We approximate this relation by polynomials for an easier reference to the rotational characteristics in different colors. The total (peak-to-peak) amplitudes of the large majority (94%) of these variables span the range of 0.005 to 0.04 mag. The periods cover a range from 2.5 to 15 days. These data strongly confirm that Praesepe and the Hyades have the same gyrochronological ages. Regarding the two planet hosts, Pr0211 (the one with the shorter orbital period) has a rotational period that is ~2 days shorter than the one expected from the main rotational pattern in this cluster. This, together with other examples discussed in the paper, may hint that star-planet interaction via tidal dissipation can be significant in some cases in the rotational evolution of stars hosting Hot Jupiters.Comment: 17 pages, 13 figures, 5 tables; accepted for publication in MNRA

Noise model for a dual frequency comb beat

Cette thèse porte sur le raffinement d’un modèle du bruit utilisé pour des mesures spectroscopiques réalisées avec des peignes de fréquences optiques. La majorité des travaux antérieurs utilisaient des peignes de fréquences où le glissement (chirp) est minimisé, en supposant que tout glissement différentiel entre les peignes allait réduire le rapport signal sur bruit. L’hypothèse sous-jacente était que l’impact du bruit multiplicatif serait augmenté, le glissement lui permettant d’agir plus longtemps sur le signal d’interférence. Cependant, d’autres recherches indiquaient plutôt contraire : le chirp pourrait améliorer la mesure. Cette thèse cherche à augmenter la compréhension du comportement du bruit lorsque les peignes ont des glissements différentiels. De plus, celle-ci apporte de nouvelles évidences sur l’utilité du chirp dans ce type de mesure. À cet effet, nous avons fait une révision bibliographique des modèles du bruit dans les peignes de fréquences optiques. Ensuite, du point de vue théorique, nous avons analysé les effets du chirp sur les bruits additifs et multiplicatifs. Pour le bruit d’intensité, nous avons proposé un modèle phénoménologique décrivant le comportement de l’émission spontanée amplifiée (ASE) dans un laser à verrouillage de mode par rotation non linéaire de polarisation. Les spectres des peignes et leurs battements ont été caractérisés en portant une attention particulière à leur relation avec l’ASE. La thèse permet de conclure que le chirp différentiel n’affecte pas les niveaux des densités spectrales de bruit. Grâce au glissement différentiel de fréquence, il est possible d’envoyer plus puissance à l’échantillon et ainsi améliorer le rapport signal sur bruit des instruments à peignes de fréquence. D’un autre côté, la caractérisation de l’ASE a établi sa nature non-stationnaire. Elle a aussi expliqué des attributs spectraux qui sont observés régulièrement dans les signaux de battement des peignes. Finalement, en supposant que l’ASE circule largement dans une cavité opérée sous le seuil, sa caractérisation fournit une méthode pour estimer le déphasage non linéaire que subit le train d’impulsions femtosecondes.This thesis proposes a noise model refinement for spectroscopic measurements using dual optical frequency combs. Until now most studies centered their efforts on noise characterization using chirp free combs based on an unproved hypothesis: measurements would get worse with chirped combs since multiplicative noises would be present over a longer duration on the interference pattern thus leading to a greater impact. However, at least one experimental result hinted to the contrary: differential chirp would actually improve the signal to noise ratio. This thesis therefore aims at increasing the understanding of noise when a differential chirp is present in a dual comb measurement. The specific goal is to provide new insights about the usefulness of chirp in this kind of measurement. With this in mind, we conducted a literature review of noise models in optical frequency combs. We subsequently analyzed the chirp’s effect in the presence of both additive and multiplicative noise. The thesis also proposes a phenomenological model to describe the amplified spontaneous emission - ASE in short pulse lasers mode locked using non linear polarization rotation. Finally the comb spectra and their beat notes are characterized putting special attention to their relation with the ASE components. As conclusions, we can report that noise power spectral density levels do not change with a differential chirp. Chirping allows sending a greater optical power through the sample, such that the measurement signal to noise ratio can be improved. On the other hand, the ASE characterization established its non-stationary nature and explained very well characteristic features routinely observed in dual comb beat notes that were not fully understood. Finally, assuming the ASE experiences a sub threshold linear cavity allows using theses features to estimate the non linear phase shift experienced by the modelocked pulse train in the laser cavity