Video Quality Assessment in Underwater Acoustic Networks

Fecha de Lectura de Tesis Doctoral: 23 de mayo de 2018.Las imágenes subacuáticas reciben una atención cada vez mayor por parte de la comunidad científica dado que las fotografías y los vídeos son herramientas de gran valor en el estudio del entorno oceánico que cubre el 90% de la biosfera de nuestro planeta. Sin embargo, las Redes de Sensores Submarinas deben enfrentarse al canal hostil que el agua de mar constituye. Las comunicaciones de medio rango son sólo posibles con modems acústicos de capacidades muy limitadas con tasas binarias de pico de unas decenas de kbps. En transmisión de vídeo, estas reducidas tasas binarias fuerzan una compresión elevada que produce niveles de distorsión mucho mayores que en otros entornos. Además, los usuarios de vídeo submarino son oceanógrafos u otros especialistas con una percepción de la calidad diferente a la de un grupo genérico de usuarios. Las peculiaridades descritas exigen un estudio dedicado de la evaluación de calidad de vídeo para redes submarinas. Esta tesis doctoral aborda el problema de la evaluación de calidad de vídeo y presenta contribuciones en las dos áreas principales de esta disciplina: evaluación subjetiva y evaluación objetiva. La referencia para la percepción de calidad en cualquier servicio es la opinión de los usuarios y, por tanto, un análisis de la calidad subjetiva es el primer paso en este trabajo. Se presentan el diseño experimental y los resultados de un test de acuerdo a métodos psicométricos estándares. Los participantes del test fueron científicos del océano y las secuencias de vídeo utilizadas fueron grabadas en campañas de exploración y procesadas para simular las condiciones de las comunicaciones submarinas. Los resultados experimentales muestran como los vídeos son útiles para tareas científicas incluso en condiciones de muy baja tasa binaria. Los métodos de evaluación de la calidad objetiva son algoritmos diseñados para calcular puntuaciones de calidad

Enhancing physical activity coaching through personalized motivational strategies and self-adaptive goal-setting: development of self-adaptive processes in a monitoring and coaching smartphone application

Dissertação para obtenção do Grau de Mestre em Engenharia BiomédicaThe rising age of the European population brings increased costs in healthcare mainly related to the management of chronic diseases. Regular physical activity has been shown to help in the prevention and control of disease risk. Mobile phones have provided promising and emergent ways of promoting healthy lifestyles, allowing real-time monitoring and coaching to be delivered at any time and any place. The presented work adds new features to the Activity Coach, an ambulatory feedback system that aims to encourage physical activity. The Integral of the Modulus of Body Acceleration (IMA) is the unit used as an estimate for energy expenditure. Although previous research demonstrated the potential of this system, results also showed that adherence drops after a few weeks. The primary goal of this research was to design, implement, and test adaptive goal-setting and personalized feedback strategies in order to encourage physical activity. Regarding the self-adaptive goal-setting feature, the goal for each day is defined automatically based on the physical activity performed at that day of the week since the beginning of the intervention. Hence, the intention is to help the user to increase or maintain his level of physical activity taking his daily routine as a reference. The second element added to the system regards motivational feedback messages, a key factor in interventions aiming at behavior change. Based on the levels of self-efficacy, stage-of-change, and daily activity, the user is assigned to one of the six pre-defined feedback strategies in the system. The content of the motivational cues depends on the selected feedback strategy. The evaluation of the system focused on providing better understandable and more accurate feedback to the user. To do so, we evaluated the challenge and attainability of the goals provided to the user with (1) data acquired during previous studies, and (2) newly gathered data from a single-subject study. As part of the evaluation, we translated IMA counts into ‘steps’, a commonly understandable measure for physical activity, comparing the data acquired from the Activity Coach sensor with a Fitbit, a commercially available pedometer. Although further tests with more subjects and different activities should be performed, we suggest that the default values set to the system are in agreement with the Goal-Setting Theory providing challenging and attainable goals. The results from this research will be used in future experiments using the Activity Coach and can be adapted to other ambulatory feedback systems regarding promotion of physical activity