Kalman-Filter-Based Orientation Determination Using Inertial/Magnetic Sensors: Observability Analysis and Performance Evaluation

In this paper we present a quaternion-based Extended Kalman Filter (EKF) for estimating the three-dimensional orientation of a rigid body. The EKF exploits the measurements from an Inertial Measurement Unit (IMU) that is integrated with a tri-axial magnetic sensor. Magnetic disturbances and gyro bias errors are modeled and compensated by including them in the filter state vector. We employ the observability rank criterion based on Lie derivatives to verify the conditions under which the nonlinear system that describes the process of motion tracking by the IMU is observable, namely it may provide sufficient information for performing the estimation task with bounded estimation errors. The observability conditions are that the magnetic field, perturbed by first-order Gauss-Markov magnetic variations, and the gravity vector are not collinear and that the IMU is subject to some angular motions. Computer simulations and experimental testing are presented to evaluate the algorithm performance, including when the observability conditions are critical

Accelerometry-Based Classification of Human Activities Using Markov Modeling

Accelerometers are a popular choice as body-motion sensors: the reason is partly in their capability of extracting information that is useful for automatically inferring the physical activity in which the human subject is involved, beside their role in feeding biomechanical parameters estimators. Automatic classification of human physical activities is highly attractive for pervasive computing systems, whereas contextual awareness may ease the human-machine interaction, and in biomedicine, whereas wearable sensor systems are proposed for long-term monitoring. This paper is concerned with the machine learning algorithms needed to perform the classification task. Hidden Markov Model (HMM) classifiers are studied by contrasting them with Gaussian Mixture Model (GMM) classifiers. HMMs incorporate the statistical information available on movement dynamics into the classification process, without discarding the time history of previous outcomes as GMMs do. An example of the benefits of the obtained statistical leverage is illustrated and discussed by analyzing two datasets of accelerometer time series

A machine learning framework for gait classification using inertial sensors: Application to elderly, post-stroke and huntington’s disease patients

Machine learning methods have been widely used for gait assessment through the estimation of spatio-temporal parameters. As a further step, the objective of this work is to propose and validate a general probabilistic modeling approach for the classification of different pathological gaits. Specifically, the presented methodology was tested on gait data recorded on two pathological populations (Huntington’s disease and post-stroke subjects) and healthy elderly controls using data from inertial measurement units placed at shank and waist. By extracting features from group-specific Hidden Markov Models (HMMs) and signal information in time and frequency domain, a Support Vector Machines classifier (SVM) was designed and validated. The 90.5% of subjects was assigned to the right group after leave-one-subject-out cross validation and majority voting. The long-term goal we point to is the gait assessment in everyday life to early detect gait alterations

Pre-impact fall detection: optimal sensor positioning based on a machine learning paradigm

The aim of this study was to identify the best subset of body segments that provides for a rapid and reliable detection of the transition from steady walking to a slipping event. Fifteen healthy young subjects managed unexpected perturbations during walking. Whole-body 3D kinematics was recorded and a machine learning algorithm was developed to detect perturbation events. In particular, the linear acceleration of all the body segments was parsed by Independent Component Analysis and a Neural Network was used to classify walking from unexpected perturbations. The Mean Detection Time (MDT) was 3516123 ms with an Accuracy of 95.4%. The procedure was repeated with data related to different subsets of all body segments whose variability appeared strongly influenced by the perturbation-induced dynamic modifications. Accordingly, feet and hands accounted for most data information and the performance of the algorithm were slightly reduced using their combination. Results support the hypothesis that, in the framework of the proposed approach, the information conveyed by all the body segments is redundant to achieve effective fall detection, and suitable performance can be obtained by simply observing the kinematics of upper and lower distal extremities. Future studies are required to assess the extent to which such results can be reproduced in older adults and in different experimental conditions

Emigración y retención de Palinurus elephas (Fabricius, 1787) en un área marina protegida del Mediterráneo central occidental

This study describes the results obtained by applying the Arnason Schwartz multistate mark-recapture model to eight years of data collected in and around a small no-fishing marine protected area (MPA; 4 km2) in the central western Mediterranean. From 1997 to 2004, a total of 4044 specimens of Palinurus elephas (Fabr., 1787) were tagged and 317 recaptured. The most parsimonious model which best explained the data variability was that of a temporally constant rate of apparent survival and movement in each of the two strata. The absence of any temporal influence in the apparent survival rate inside the no-take area suggested that spillover and mortality are constant for each period of the study. The lower apparent survival rate in surrounding zones than inside the MPA (0.26 ± 0.04 (SE) vs 0.94 ± 0.03 (SE)) is presumed to be a function of fishing effort. A continuous movement of P. elephas across the boundary of the small MPA was also tested. This information on retention of lobsters in the MPA contributes to our understanding of the effect of introducing MPAs into a managed commercial fishery system.Este estudio presenta los resultados de aplicar el modelo multiestado de marcado y recaptura de Arnason Schwartz a una serie de ocho años de datos recolectados en el interior y alrededor de una pequeña área marina protegida (AMP) vedada a la pesca (4 km2) del Mediterráneo central occidental. Desde 1997 a 2004, un total de 4044 ejemplares de Palinurus elephas (Fabr., 1787) fueron marcados, de los cuales 317 fueron recapturados. El modelo más parsimonioso que explicó mejor la variabilidad de los datos fue aquel con una tasa temporal constante de aparente supervivencia y movimiento entre los dos estratos. La ausencia de influencia temporal sobre la tasa de supervivencia aparente en el interior del área protegida, sugirió que el “spillover” y la mortalidad son constantes para cada periodo del estudio. La menor tasa aparente de supervivencia en zonas alrededor de la reserva respecto al interior de la misma (0.26 ± 0.04 (SE) vs 0.94 ± 0.03 (SE)) se considera que es una función del esfuerzo pesquero. Un movimiento continuo de P. elephas a través de los límites de la pequeña AMP fue evaluado. Esta información sobre la retención de langostas en el AMP contribuye a comprender el efecto de la introducción de AMPs en un sistema regulado de pesquería comercial

Emigration and retention of <i>Palinurus elephas</i> (Fabricius, 1787) in a central western Mediterranean marine protected area

Este estudio presenta los resultados de aplicar el modelo multiestado de marcado y recaptura de Arnason Schwartz a una serie de ocho años de datos recolectados en el interior y alrededor de una pequeña área marina protegida (AMP) vedada a la pesca (4 km2) del Mediterráneo central occidental. Desde 1997 a 2004, un total de 4044 ejemplares de Palinurus elephas (Fabr., 1787) fueron marcados, de los cuales 317 fueron recapturados. El modelo más parsimonioso que explicó mejor la variabilidad de los datos fue aquel con una tasa temporal constante de aparente supervivencia y movimiento entre los dos estratos. La ausencia de influencia temporal sobre la tasa de supervivencia aparente en el interior del área protegida, sugirió que el "spillover" y la mortalidad son constantes para cada periodo del estudio. La menor tasa aparente de supervivencia en zonas alrededor de la reserva respecto al interior de la misma (0.26 ± 0.04 (SE) vs 0.94 ± 0.03 (SE)) se considera que es una función del esfuerzo pesquero. Un movimiento continuo de P. elephas a través de los límites de la pequeña AMP fue evaluado. Esta información sobre la retención de langostas en el AMP contribuye a comprender el efecto de la introducción de AMPs en un sistema regulado de pesquería comercial

Movement patterns of the spiny lobster <em>Palinurus elephas</em> (Fabricius, 1787) from a central western Mediterranean protected area

Movement patterns of the spiny lobster Palinurus elephas were determined from 389 individuals (total tagged 5666) tag-recaptured inside a no-take area of the central western Mediterranean and its surrounding zone. High site association and limited movements in tagged lobsters was observed; 60.4% of lobsters moved less than 2 km from the centre of the area (site of release). No clear relationship between lobster movement pattern and sex or size was observed; however, it seemed that the largest males and females tended to be more resident, thus contributing to the rebuilding of the biomass of local lobsters. Most lobsters undertook migrations in the southwest direction. The increased availability of shelters and food towards the southwest could have contributed to the lobsters' movement. The results of our research indicate that the small size of the protected area and the scale of the movement exhibited by tagged lobsters allows a proportion of the lobster population to move out of the protected area and become susceptible to capture in the adjacent fishery

Pautas de movimiento de la langosta Palinurus elephas (Fabricius, 1787) desde un área protegida en el Mediterráneo occidental central

Movement patterns of the spiny lobster Palinurus elephas were determined from 389 individuals (total tagged 5666) tag-recaptured inside a no-take area of the central western Mediterranean and its surrounding zone. High site association and limited movements in tagged lobsters was observed; 60.4% of lobsters moved less than 2 km from the centre of the area (site of release). No clear relationship between lobster movement pattern and sex or size was observed; however, it seemed that the largest males and females tended to be more resident, thus contributing to the rebuilding of the biomass of local lobsters. Most lobsters undertook migrations in the southwest direction. The increased availability of shelters and food towards the southwest could have contributed to the lobsters’ movement. The results of our research indicate that the small size of the protected area and the scale of the movement exhibited by tagged lobsters allows a proportion of the lobster population to move out of the protected area and become susceptible to capture in the adjacent fishery.Se determinaron las pautas de movimiento de 389 individuos de la langosta Palinurus elephas (total marcados 5666) marcados y recapturados en el interior de un área protegida (sin captura) así como de su área circundante. En las langostas marcadas se observó una elevada asociación al lugar de liberación, así como movimientos limitados: el 60.4% de las langostas se movieron menos de 2 km desde el centro del área de liberación. No se observó ninguna clara relación entre las pautas de movimiento de las langostas y su sexo y talla; no obstante, hay una tendencia a que los machos y hembras grandes muestren un comportamiento más residente, contribuyendo así al aumento de la biomasa local. La mayor parte de langostas mostró migraciones en dirección sudoeste. La mayor disponibilidad de refugios y alimento hacia el sudoeste pudo haber contribuído al movimiento de las langostas. Los resultados de este estudio indican que el pequeño tamaño del área protegida y la escala de movimientos mostrados por las langostas marcadas permite a una porción de la población su salida del área protegida y su susceptibilidad a la captura en la pesquería adyacente