Submitted in fulfillment of the requirements of the Doctor of Technology Degree in Information Technology, Durban University of Technology, Durban, South Africa, 2014. / The work described in this thesis summarizes the author’s contributions to the design, development and testing of embedded solutions for maritime Radio and Satellite tracking and detecting systems. In order to provide reliable tracking and detecting facilities of ships have to be integrated Convectional Maritime Radio Communications (CMRC) and Maritime Mobile Satellite Communications (MMSC) systems. On the other hand, Global Mobile Satellite Communications (GMSC) as a part of Global Communication Satellite Systems (GCSS) has to be integrated with Global Navigation Satellite Systems (GNSS) of the US GPS or Russian GLONASS systems. The proposed local maritime Radio VHF Communication, Navigation and Surveillance (CNS) systems and devices, such as Radio Automatic Identification System (R-AIS) or VHF Data Link (VDL), Radio Automatic Dependent Surveillance - Broadcast (RADS-B) and GNSS Augmentation VDL-Broadcast (GAVDL-B) are introduced. The new technology deigns of global Satellite CNS maritime equipment and systems, such as Global Ship Tracking (GST) as enhanced Long Range Identification and Tracking (LRIT), Satellite AIS (S-AIS), Satellite Data Link (SDL), Satellite Automatic Dependent Surveillance - Broadcast (SADS-B) and GNSS Augmentation SDL (GASDL) are discussed and benefits of these new technologies and solution for improved Ship Traffic Control (STC) and Management (STM) are explored. The regional maritime CNS solutions via Stratospheric Communication Platforms (SCP), tracking of ships at sea via Space Synthetic Aperture Radar (SSAR) or Inverse Synthetic Aperture Radar (ISAR)and Ground Synthetic Aperture Radar (GSAR) are described. The special tracking systems for collision avoidance with enhanced safety and security at sea including solutions of captured ships by pirates through aids of the MMSC, SCP and Radars are introduced and the testing methodologies employed to qualify embedded hardware for this environment are presented. During the voyage of the ship in good weather conditions and when navigation devices on the bridge are in order, then can be used very well AIS, LRIT, anti-collision Radar and other on-board equipment. However, at very bad weather conditions sometimes surveillance Radar and Radio HF Transceiver cannot work, but may work only GPS Receiver and L/C-band Satellite Transceiver, while Radio VHF Transceiver will have extremely reduced coverage, what is not enough for safe navigation and collision avoidance. Therefore, during those critical circumstances, when the safety of navigations very important, it will be not necessary to ask "Where am I", but "Where are nearby ships around me"? At this point, it should be needed the newest techniques and equipment for enhanced STC and STM, such as GST, S-AIS, SDL, SADS-B and GASDL. Terrorists exploit surprise in successful pirate actions worldwide and security forces are generally unaware of the source of these attacks at sea. In today’s information age, terror threats may originate with transnational organizations or exploit the territory of failed, weak or neutral states. Thus, countering piracy by eliminating the terrorists on land is the best solution, however, it might not be feasible and even though it’s successful could require many years. In the thesis, the general overview of Radio and Mobile Satellite Systems (MSS) for ship communication and tracking systems is conducted as well, including the space platform and orbital mechanics, horizon and geographic satellite coordinates and classification of spacecraft by Geostationary Earth Orbits (GEO) and Non-GEO orbits.

Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 1997. / This dissertation considers the feasibility of using atmospheric drag to control constellations of micro-satellites in low Earth orbits. The constellation control requirements include an acquisition phase and a maintenance phase. Optimal strategies are designed to control the relative positions of the satellites during these two phases. It is shown that the feasibility and success of the strategies depend on many factors, including the satellite properties and orbital configuration. A nominal test constellation is presented and used as a generic example for the application of the control strategies. The dissertation also focuses on the accurate modelling and simulation of a typical low Earth orbit satellite, moving under the influence of a variety of significant orbit perturbation forces. The simulations form an integral part of the study and are used to verify the application of all the proposed control strategies.

Thesis (PhD (Electronic Engineering))--University of Stellenbosch, 2009. / The downloading of images is a bottleneck in the image acquisition chain for low earth orbit, remote sensing satellites. An on-board image quality assessment system could optimise use of available downlink time by prioritising images for download, based on their quality. An image quality assessment system based on measuring image degradations is proposed. Algorithms for estimating degradations are investigated. The degradation types considered are cloud cover, additive sensor noise and the defocus extent of the telescope. For cloud detection, the novel application of heteroscedastic discriminant analysis resulted in better performance than comparable dimension reducing transforms from remote sensing literature. A region growing method, which was previously used on-board a micro-satellite for cloud cover estimation, is critically evaluated and compared to commonly used thresholding. The thresholding method is recommended. A remote sensing noise estimation algorithm is compared to a noise estimation algorithm based on image pyramids. The image pyramid algorithm is recommended. It is adapted, which results in smaller errors. A novel angular spectral smoothing method for increasing the robustness of spectral based, direct defocus estimation is introduced. Three existing spectral based defocus estimation methods are compared with the angular smoothing method. An image quality assessment model is developed that models the mapping of the three estimated degradation levels to one quality score. A subjective image quality evaluation experiment is conducted, during which more than 18000 independent human judgements are collected. Two quality assessment models, based on neural networks and splines, are tted to this data. The spline model is recommended. The integrated system is evaluated and image quality predictions are shown to correlate well with human quality perception.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: The Electronic Systems Laboratory at Stellenbosch University is currently developing a fully 3-axis controlled Attitude Determination and Control Subsystem (ADCS) for CubeSats. This thesis describes the design and development of an Onboard Computer (OBC) suitable for ADCS application. A separate dedicated OBC for ADCS purposes allows the main CubeSat OBC to focus only on command and data handling, communication and payload management. This thesis describes, in detail the development process of the OBC. Multiple Microcontroller Unit (MCU) architectures were considered before selecting an ARM Cortex-M3 processor due to its performance, power efficiency and functionality. The hardware was designed to be as robust as possible, because radiation tolerant and redundant components could not be included, due to their high cost and the technical constraints of a CubeSat. The software was developed to improve recovery from lockouts or component failures and to enable the operational modes to be configured in real-time or uploaded from the ground station. Ground tests indicated that the OBC can handle radiation-related problems such as latchups and bit-flips. The peak power consumption is around 500 mW and the orbital average is substantially lower. The proposed OBC is therefore not only sufficient in its intended application as an ADCS OBC, but could also stand in as a backup for the main OBC in case of an emergency. / AFRIKAANSE OPSOMMING: Die Elektroniese Stelsels Laboratorium by die Universiteit van Stellenbosch is tans besig om ’n volkome 3-as gestabiliseerde oriëntasiebepaling en -beheerstelsel (Engels: ADCS) vir ’n CubeSat te ontwikkel. Hierdie tesis beskryf die ontwerp en ontwikkeling van ’n aanboordrekenaar (Engels: OBC) wat gebruik kan word in ’n ADCS. ’n Afsonderlike OBC wat aan die ADCS toegewy is, stel die hoof-OBC in staat om te fokus op beheer- en datahantering, kommunikasie en loonvragbestuur. Hierdie tesis beskryf breedvoerig die werkswyse waarvolgens die OBC ontwikkel is. Verskeie mikroverwerkers is as moontlike kandidate ondersoek voor daar op ’n ARM Cortex-M3-gebaseerde mikroverwerker besluit is. Hierdie mikroverwerker is gekies vanweë sy spoed, effektiewe kragverbruik en funksionaliteit. Die hardeware is ontwikkel om so robuust moontlik te wees, omdat stralingbestande en oortollige komponente weens kostebeperkings, asook tegniese beperkings van ’n CubeSat, nie ingesluit kon word nie. Die programmatuur is ontwikkel om van ’n uitsluiting en ’n komponentfout te kan herstel. Verder kan programme wat tydens vlug in werking is, verstel word en vanaf ’n grondstasie gelaai word. Grondtoetse het aangedui dat die OBC stralingverwante probleme, soos ’n vergrendeling (latchup) of bis-omkering (bit-flip), kan hanteer. Die maksimum kragverbruik is ongeveer 500 mW en die gemiddelde wentelbaankragverbruik is beduidend kleiner. Die voorgestelde OBC is dus voldoende as ADCS OBC asook hoof-OBC in geval van nood.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2008. / A communications protocol is designed for real time control and data handling for a Nanosatellite application. The communication protocol is based on the Controller Area Network (CAN) technology. The protocol handles different message types such as time synchronization, telecommand messages, telemetry acquisition, unsolicited telemetry messages, large file transfers and debug messages. The design of the protocol entails finding a suitable target microcontroller in which the protocol implementation is demonstrated. This requires consideration of a number of development factors such as cost, complexity, availability, reliability and operational environment (space). The AVR AT90CAN128 microcontroller was chosen as a target microcontroller as it gave most of the required factors mentioned above. The protocol implementation involves developing low level software drivers, the middleware and the application programs to demonstrate handling of each supported message. In the implementation the media access scheme and low layer communication is provided by the CAN low level kernel (physical and data link layers). The protocol performance was evaluated by measuring the software response latencies, the bus throughputs and the software efficiencies. Power consumption due to CAN communication was also measured. System reliability was tested by loading the CAN bus with extreme communication traffic and letting the system run for a long time. The observation was that messages were handled consistently.

Subtropical deforestation in Latin America is thought to be driven by demand for agricultural land, particularly to grow soybeans. However, existing remote sensing methods that can differentiate crop types to verify this hypothesis require high spatial or spectral resolution data, or extensive ground truth information to develop training sites, none of which are freely available for much of the world. I developed a new method of crop classification based on the phenological signatures of crops extracted from multi-temporal MODIS vegetation indices. I tested and refined this method using the USDA Cropland Data Layer from Kansas, USA as a reference. I then applied the method to classify crop types for a study site in Pellegrini, Santiago Del Estero, Argentina. The results show that this method is unable to effectively separate summer crops in Pellegrini, but can differentiate summer crops and non-summer crops. Unmet assumptions about agricultural practices are primarily responsible for the ineffective summer crop classification, underlining the need for researchers to have a complete understanding of ground conditions when designing a remote sensing analysis.

Lidar is able to provide height and cover information which can be used to estimate selected forest attributes precisely. However, for users to evaluate whether the additional cost and complication associated with using Lidar merits adoption requires that the protocol to use lidar be thoroughly described and that a basis for selection of design parameters such as number of field plots and lidar pulse density be described. In our first analysis, we examine these issues by looking at the effects of pulse density and sample size on estimation when wall-to-wall lidar is used with a regression estimator. The effects were explored using resampling simulations. We examine both the effects on precision, and on the validity of inference. Pulse density had almost no effect on precision for the range examined, from 3 to .0625 pulses / m��. The effect of sample size on estimator precision was roughly in accordance with the behavior indicated by the variance estimator, except that for small samples the variance estimator had positive bias (the variance estimates were too small), compromising the validity of inference. In future analyses we plan to provide further context for wall-to-wall lidar-assisted estimation. While there is a lot of literature on modeling, there is limited information on how lidar-assisted approaches compare to existing methods, and what variables can or cannot be acquired, or may be acquired with reduced confidence. We expand our investigation of estimation in our second analysis by examining lidar obtained in a sampling mode in combination with Landsat. In this case we make inference about the feasibility of a lidar-assisted estimation strategy by contrasting its variance estimate with variance estimates from a variety of other sampling designs and estimators. Of key interest was how the precision of a two-stage estimator with lidar strips compared with a plot-only estimator from a simple random sampling design. We found that because the long and narrow lidar strips incorporate much of the landscape variability, if the number of lidar strips was increased from 7 to 15 strips, the precision of estimators with lidar can exceed that of estimators applied to plot-only SRS data for a much larger number of plots. Increasing the number of lidar strips is considered to be highly viable since the costs of field plots can be quite expensive in Alaska, often exceeding the cost of a lidar strip. A Landsat-assisted approach used for either an SRS or a two-stage sample was also found to perform well relative to estimators for plot-only SRS data. This proved beneficial when we combined lidar and Landsat-assisted regression estimators for two-stage designs using a composite estimator. The composite estimator yielded much better results than either estimator used alone. We did not assess the effects of changing the number of lidar strips in combination with using a composite estimator, but this is an important analysis we plan to perform in a future study. In our final analysis we leverage the synergy between lidar and Landsat to improve the explanatory power of auxiliary Landsat using a multilevel modeling strategy. We also incorporate a more sophisticated approach to processing Landsat which reflects temporal trends in individual pixels values. Our approach used lidar as an intermediary step to better match the spatial resolution of Landsat and increase the proportion of area overlapped between measurement units for the different sources of data. We developed two separate approaches for two different resolutions of data (30 m and 90 m) using multiple modeling alternatives including OLS and k nearest neighbors (KNN), and found that both resolution and the modeling approach affected estimates of residual variability, although there was no combination of model types which was a clear winner for all responses. The modeling strategies generally fared better for the 90 m approaches, and future analyses will examine a broader range of resolutions. Fortunately the approaches used are fairly flexible and there is nothing prohibiting a 1000 m implementation. In the future we also plan to look at using a more sophisticated Landsat time-series approach. The current approach essentially dampened the noise in the temporal trend for a pixel, but did not make use of information in the trend such as slope or indications of disturbance ��� which may provide additional explanatory power. In a future study we will also incorporate a multilevel modeling into estimation or mapping strategies and evaluate the contribution of the multilevel modeling strategy relative to alternate approaches. / Graduation date: 2013 / Access restricted to the OSU Community at author's request from June 21, 2012 - Dec. 21, 2012

Most present day spacecrafts have large interconnected solar panels. The dynamic behavior of the spacecraft in orbit can be modeled as a free rigid mass with flexible elements attached to it. The natural frequencies of such spacecrafts with deployed solar panels are very low. The low values of the natural frequencies pose difficulties for maneuvering the spacecraft. The control torque required to maneuver the spacecraft is influenced by the flexibility of the solar arrays. The control torque sets up transient oscillations in the flexible solar panels which in turn induces disturbances in the rigid satellite body and the payload within. Therefore the payload operations can be carried out only after the disturbances die out. For any reduction of the above disturbances it is necessary to understand the dynamic behavior of such systems to an applied torque. The present work first studies the nature of the disturbances. The influence of structural parameters on these disturbances is then investigated. Finally, the use of passive damping treatment using viscoelastic material is investigated for the reduction of the disturbances. In order to understand the nature of vibrations induced in the flexible appendages of a satellite during maneuvers, we model the maneuver loads in terms of applied angular acceleration as well as varying torque. The transient decay of the disturbance of the rigid element is characterized by the dynamic characteristics of the flexible panels or appendages. It is shown that by changing the stiffness of the panel the response of the rigid element can be modified. A simple model consisting of an Euler-Bernoulli beam attached to a free mass is next considered. The influence of various parameters of the EulerBernoulli beam in mitigating vibration and thereby the disturbance in the rigid mass is investigated. As the response of the rigid system mounted with the large flexible panels are influenced by the dynamics of the flexible panels, reduction of these disturbances can be achieved by reducing the vibration in the flexible panels. Therefore application of viscoelastic materials for passive damping treatment is investigated. The loss factor of a structure is significantly improved by using constrained viscoelastic layer damping treatment. However providing a constrained layer damping treatment on the entire structure is very inefficient in terms of the additional mass involved. Therefore damping material is applied at suitable optimal locations. In previous studies reported in literature, modal strain energy distribution in the viscoelastic material as well as the base structure is used as a tool to arrive at the optimum location for the damping treatment. It is shown in this study that such locations selected are not the optimum. A new approach is proposed in this study by which both the above shortcomings are overcome. It is shown that use of a parameter that is the ratio of the strain in the viscoelastic material to the angle of flexure is a more reliable measure in arriving at optimal locations for the application of constrained viscoelastic layers. The method considers the deformations in the viscoelastic material and it is shown that significant values of loss factors are achieved by providing material in a small region alone. We also show that loss factor can be improved by providing damping material near the interface region. The loss factor can be further improved by incorporating spacers by using spacer material having higher extensional modulus. Also shown is the fact that loss factor is unaffected by the shear modulus of the spacer material. Experiments have been conducted to validate these results. In a related study we consider honeycomb type flexible structures since in most of the spacecraft applications honeycomb sandwich constructions are employed. But loss factors of sandwich panels with constrained layer damping treatment are seldom discussed in the literature. Use of viscoelastic layers to improve the loss factors of the honeycomb sandwich beams is explored. The results show that the loss factors are enhanced by increasing the inplane stiffness of the constraining layer. These conclusions too are validated by experimental results. Finally a typical satellite with flexible solar panels is considered, and the use of the viscoelastic material for improving the damping is demonstrated.

University of Macau / Faculty of Law

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