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The aim of' this investigation is to determine the combination of signal coding and modulation for satellite links, that, for a given degree of equipment complexity needed for the detection of the received signal, achieves the best tolerance to noise. Computer simulation tests and theoretical analyses are used to compare the various proposed signal designs The trellis coded M-ary phase-shift-keyed (MPSK) modulation method is introduced as the scheme for which different codes are to be devised. A class of known binary convolutional codes for 8 and 16 PSK signals is studied, and new correlative-level codes using modulo-M arthimetic are designed for MPSK signals. The soft-decision maximum likelihood Viterbi decoding algorithm is considered for the two proposed signal designs, and a more conventional near-maximum likelihood (reduced-state Viterbi) decoding scheme is also investigated for both types of coded signals. Two novel decoding schemes, derived from a more conventional near-maximum likelihood decoder, are proposed for coded 8PSK signals. In both decoders the amount of computation involved in decoding each data-symbol is adjusted to meet the prevailing noise level in transmission. Results of extensive computer simulation tests for both decoding schemes are presented. These results suggest that the new schemes come very close to achieving the maximum likelihood decoding of the coded signals without, however, requiring nearly as much storage and computation per decoded data symbol as does the Viterbi decoder. The carrier-phase synchronisation prob1em in a coherent trellis coded MPSK system is investigated. Eight new rotationally invariant rate-2/3 and rate-3/U convolutional codes for 8 and 16 PSK signals are designed. The new coded MPSK signals, when combined with a simple phase-error correction system proposed for the receiver, are able to tolerate the likely carrier-phase changes in the reference carriers of the coherent demodulation process and therefore avoid the prolonged error bursts that are otherwise caused in the decoded data symbols by such phase shifts. coding gains of the majority of the new codes The asymptotic here are either the same as, or come close to, those of the best known but not rotationally invariant convolutional codes of the same rates.

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The Scottish Office Department of Agriculture and Fisheries Department has been concerned to know the area of bracken (Pteridium aquilinum ) in Scotland and how rapidly it is spreading. It offers a potential danger to animal health and a devaluation of land for agricultural practice. Bracken is present in patches which are often difficult to delimit because of variable density and appearance throughout the year and is not consistently identifiable at a single minimum spatial resolution. Bracken provided a candidate vegetation type for prototyping a knowledge-based system (KBS) which synthesized environmental data expressed spatially, with knowledge on vegetation dynamics and vegetation succession in particular. Temporal models of vegetation types, which have different degrees of reliability with analysis of static spatial data were incorporated. The knowledge-based system permits the user access to knowledge about botany, ecology, mapping, image processing and spatial data analysis for an informed and informative answer to their query. Bracken was mapped at three experimental sites using land survey, photogrammetric techniques and satellite image processing to quantify the extent of bracken and bracken change. An existing data model was enhanced by building-in the hierarchy of survey observations and associated error bands. The model was then implemented within an expert system shell with KBS routines written in POP-11 and Fortran. The coupling of the GIS and KBS routines was of the form of: 1. organisation of the transfer of descriptive values as parameters between the data-models of the KBS and the GIS routines and 2. read/write of the spatial data into the data-models for analyses by KBS routines.

This thesis documents an investigation of the effect of solar radiation pressure on the motion of an artificial satellite. Consideration is given to the methods required for the inclusion of the discontinuous effect of the Earth's shadow. The analysis resulting from the description of a deformed diffusely reflecting balloon satellite and an algorithm describing the effects of Earth reflected solar radiation pressure are developed, culminating in the application of the derived theory to the orbital data of the balloon satellite, Explorer 19.

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La détermination de la composition chimique des aérosols atmosphériques est essentielle pour le climat terrestre et l’environnement. Néanmoins, les mesures in situ qui permettent d’accéder à cette composition sont limitées et les modèles de chimie-transport peuvent ne pas bien représenter la réalité. Notre travail de thèse a consisté à développer une nouvelle approche afin de remonter à la composition des aérosols à grande échelle par télédétection. Les modèles de mélange des composants des aérosols, soit par proportion en volume soit par l’approximation de Maxwell Garnett qui relient les propriétés optiques à la composition, ont été incorporés dans l’algorithme de restitution des propriétés atmosphériques (GRASP). La nouveauté du concept réside dans la restitution directe des composants chimiques de l’aérosol plutôt que dans une estimation indirecte à partir des propriétés optiques retrouvées. Les tests synthétiques ont montré une sensibilité des observations du satellite POLDER/PARASOL à la présence d’éléments chimiques clés des aérosols. La méthodologie a ensuite été appliquée aux mesures réelles. Les caractéristiques optiques dérivées de PARASOL en utilisant le module de composition chimique ont montré un bon accord (R de ~ 0,9 pour l’épaisseur optique) avec nos mesures de référence — le réseau AERONET. La méthodologie a aussi été appliquée aux mesures de AERONET. Les variabilités spatiale et temporelle de la composition de l’aérosol ainsi retrouvée correspondent bien à nos attentes. La composition obtenue a également été validée à l’aide de données de campagne de terrain et a pu être comparée avec les simulations réalisées avec le modèle chimie-transport GOCART. / Determination of atmospheric aerosol chemical composition has a great importance for Earth’s climate and environment. However, in situ measurements that enable determination of aerosol composition are limited in time and space, while simulations by chemical transport models may not accurately describe the reality. The current thesis presents a novel methodology for monitoring of aerosol composition by remote sensing on large spatial and temporal scale. Namely, the volume-weighted and Maxwell Garnett models, which link the aerosol optical properties and chemical composition, were incorporated into the first versatile algorithm (GRASP) that derives the atmospheric properties from remote sensing. The concept proposes the direct retrieval of fractions of aerosol chemical components instead of post-processing estimate of the aerosol composition from the retrieved optical properties (refractive index, aerosol sizes). The tests showed sufficient sensitivity of the POLDER/PARASOL satellite observations to presence of key aerosol chemical elements. Then, the methodology was applied for the real PARASOL measurements. The aerosol optical characteristics derived from PARASOL using the chemical composition module demonstrated a good agreement with our reference measurements – AERONET ground-based network (e.g., R of ~ 0.9 for aerosol optical thickness). The methodology was then applied to the AERONET measurements as well. The obtained spatial and temporal patterns of aerosol composition agree well with known physical expectations. The retried aerosol composition was validated using available field campaign data and inter-compared with GOCART chemical transport model simulations.

Satellite constellations provide the infrastructure to implement some of the most important global services of our times both in civilian and military applications, ranging from telecommunications to global positioning, and to observation systems. Flower Constellations constitute a set of satellite constellations characterized by periodic dynamics. They have been introduced while trying to augment the existing design methodologies for satellite constellations. The dynamics of a Flower Constellation identify a set of implicit rotating reference frames on which the satellites follow the same closed-loop relative trajectory. In particular, when one of these rotating reference frames is “Planet Centered, Planet Fixed”, then all the orbits become compatible (or resonant) with the planet; consequently, the projection of the relative path on the planet results in a repeating ground track. The satellite constellations design methodology currently most utilized is the Walker Delta Pattern or, more generally, Walker Constellations. The set of orbital planes and initial spacecraft positions are represented by a set of only three integers and two real parameters rather than by all the orbital elements; Flower Constellations provide a more general framework in which most of the former restrictions are removed, by allowing the use of resonant elliptical orbits. Flower Constellations can represent hundreds of spacecraft with a set of 6 integers and 5 real parameters only and existing constellations can be easily reproduced. How to design a Flower Constellation to satisfy specific mission requirements is an important problem for promoting the acceptance of this novel concept by the space community. Therefore one of the main goals of this work is that of proposing design techniques that can be applied to satisfy practical mission requirements. The results obtained by applying Global optimization techniques, such as Genetic Algorithms, to some relevant navigation and Earth observation space-based systems show that the Flower Constellations not only are as effective asWalker Constellations, but can also be applied to non-traditional constellation problem domains, such as regional coverage and reconnaissance.