VNect: Real-time 3D Human Pose Estimation with a Single RGB Camera

We present the first real-time method to capture the full global 3D skeletal pose of a human in a stable, temporally consistent manner using a single RGB camera. Our method combines a new convolutional neural network (CNN) based pose regressor with kinematic skeleton fitting. Our novel fully-convolutional pose formulation regresses 2D and 3D joint positions jointly in real time and does not require tightly cropped input frames. A real-time kinematic skeleton fitting method uses the CNN output to yield temporally stable 3D global pose reconstructions on the basis of a coherent kinematic skeleton. This makes our approach the first monocular RGB method usable in real-time applications such as 3D character control---thus far, the only monocular methods for such applications employed specialized RGB-D cameras. Our method's accuracy is quantitatively on par with the best offline 3D monocular RGB pose estimation methods. Our results are qualitatively comparable to, and sometimes better than, results from monocular RGB-D approaches, such as the Kinect. However, we show that our approach is more broadly applicable than RGB-D solutions, i.e. it works for outdoor scenes, community videos, and low quality commodity RGB cameras.Comment: Accepted to SIGGRAPH 201

Effects of non-universal large scales on conditional structure functions in turbulence

We report measurements of conditional Eulerian and Lagrangian structure functions in order to assess the effects of non-universal properties of the large scales on the small scales in turbulence. We study a 1m $\times$ 1m $\times$ 1.5m flow between oscillating grids which produces $R_\lambda=285$ while containing regions of nearly homogeneous and highly inhomogeneous turbulence. Large data sets of three-dimensional tracer particle velocities have been collected using stereoscopic high speed cameras with real-time image compression technology. Eulerian and Lagrangian structure functions are measured in both homogeneous and inhomogeneous regions of the flow. We condition the structure functions on the instantaneous large scale velocity or on the grid phase. At all scales, the structure functions depend strongly on the large scale velocity, but are independent of the grid phase. We see clear signatures of inhomogeneity near the oscillating grids, but even in the homogeneous region in the center we see a surprisingly strong dependence on the large scale velocity that remains at all scales. Previous work has shown that similar correlations extend to very high Reynolds numbers. Comprehensive measurements of these effects in a laboratory flow provide a powerful tool for assessing the effects of shear, inhomogeneity and intermittency of the large scales on the small scales in turbulence

A continuum robotic platform for endoscopic non-contact laser surgery: design, control, and preclinical evaluation

The application of laser technologies in surgical interventions has been accepted in the clinical domain due to their atraumatic properties. In addition to manual application of fibre-guided lasers with tissue contact, non-contact transoral laser microsurgery (TLM) of laryngeal tumours has been prevailed in ENT surgery. However, TLM requires many years of surgical training for tumour resection in order to preserve the function of adjacent organs and thus preserve the patient’s quality of life. The positioning of the microscopic laser applicator outside the patient can also impede a direct line-of-sight to the target area due to anatomical variability and limit the working space. Further clinical challenges include positioning the laser focus on the tissue surface, imaging, planning and performing laser ablation, and motion of the target area during surgery. This dissertation aims to address the limitations of TLM through robotic approaches and intraoperative assistance. Although a trend towards minimally invasive surgery is apparent, no highly integrated platform for endoscopic delivery of focused laser radiation is available to date. Likewise, there are no known devices that incorporate scene information from endoscopic imaging into ablation planning and execution. For focusing of the laser beam close to the target tissue, this work first presents miniaturised focusing optics that can be integrated into endoscopic systems. Experimental trials characterise the optical properties and the ablation performance. A robotic platform is realised for manipulation of the focusing optics. This is based on a variable-length continuum manipulator. The latter enables movements of the endoscopic end effector in five degrees of freedom with a mechatronic actuation unit. The kinematic modelling and control of the robot are integrated into a modular framework that is evaluated experimentally. The manipulation of focused laser radiation also requires precise adjustment of the focal position on the tissue. For this purpose, visual, haptic and visual-haptic assistance functions are presented. These support the operator during teleoperation to set an optimal working distance. Advantages of visual-haptic assistance are demonstrated in a user study. The system performance and usability of the overall robotic system are assessed in an additional user study. Analogous to a clinical scenario, the subjects follow predefined target patterns with a laser spot. The mean positioning accuracy of the spot is 0.5 mm. Finally, methods of image-guided robot control are introduced to automate laser ablation. Experiments confirm a positive effect of proposed automation concepts on non-contact laser surgery.Die Anwendung von Lasertechnologien in chirurgischen Interventionen hat sich aufgrund der atraumatischen Eigenschaften in der Klinik etabliert. Neben manueller Applikation von fasergeführten Lasern mit Gewebekontakt hat sich die kontaktfreie transorale Lasermikrochirurgie (TLM) von Tumoren des Larynx in der HNO-Chirurgie durchgesetzt. Die TLM erfordert zur Tumorresektion jedoch ein langjähriges chirurgisches Training, um die Funktion der angrenzenden Organe zu sichern und damit die Lebensqualität der Patienten zu erhalten. Die Positionierung des mikroskopis chen Laserapplikators außerhalb des Patienten kann zudem die direkte Sicht auf das Zielgebiet durch anatomische Variabilität erschweren und den Arbeitsraum einschränken. Weitere klinische Herausforderungen betreffen die Positionierung des Laserfokus auf der Gewebeoberfläche, die Bildgebung, die Planung und Ausführung der Laserablation sowie intraoperative Bewegungen des Zielgebietes. Die vorliegende Dissertation zielt darauf ab, die Limitierungen der TLM durch robotische Ansätze und intraoperative Assistenz zu adressieren. Obwohl ein Trend zur minimal invasiven Chirurgie besteht, sind bislang keine hochintegrierten Plattformen für die endoskopische Applikation fokussierter Laserstrahlung verfügbar. Ebenfalls sind keine Systeme bekannt, die Szeneninformationen aus der endoskopischen Bildgebung in die Ablationsplanung und -ausführung einbeziehen. Für eine situsnahe Fokussierung des Laserstrahls wird in dieser Arbeit zunächst eine miniaturisierte Fokussieroptik zur Integration in endoskopische Systeme vorgestellt. Experimentelle Versuche charakterisieren die optischen Eigenschaften und das Ablationsverhalten. Zur Manipulation der Fokussieroptik wird eine robotische Plattform realisiert. Diese basiert auf einem längenveränderlichen Kontinuumsmanipulator. Letzterer ermöglicht in Kombination mit einer mechatronischen Aktuierungseinheit Bewegungen des Endoskopkopfes in fünf Freiheitsgraden. Die kinematische Modellierung und Regelung des Systems werden in ein modulares Framework eingebunden und evaluiert. Die Manipulation fokussierter Laserstrahlung erfordert zudem eine präzise Anpassung der Fokuslage auf das Gewebe. Dafür werden visuelle, haptische und visuell haptische Assistenzfunktionen eingeführt. Diese unterstützen den Anwender bei Teleoperation zur Einstellung eines optimalen Arbeitsabstandes. In einer Anwenderstudie werden Vorteile der visuell-haptischen Assistenz nachgewiesen. Die Systemperformanz und Gebrauchstauglichkeit des robotischen Gesamtsystems werden in einer weiteren Anwenderstudie untersucht. Analog zu einem klinischen Einsatz verfolgen die Probanden mit einem Laserspot vorgegebene Sollpfade. Die mittlere Positioniergenauigkeit des Spots beträgt dabei 0,5 mm. Zur Automatisierung der Ablation werden abschließend Methoden der bildgestützten Regelung vorgestellt. Experimente bestätigen einen positiven Effekt der Automationskonzepte für die kontaktfreie Laserchirurgie

In-situ defect detection systems for R2R flexible PV films

The atomic layer deposition technique (ALD) is used to apply a thin (40-100 nm thick) barrier coating of Al2O3 on polymer substrates for flexible PV cells, to minimise and control the degradation caused by water vapour ingress. However, defects appearing on the film surfaces during the Al2O3 ALD growth have been seen to be highly significant in deterioration of the PV module efficiency and lifespan [1]. In order to improve the process yield and product efficiency, it is desirable to develop an inspection system that can detect transparent barrier film defects in the production line during film processing. Off-line detection of defects in transparent PV barrier films is difficult and time consuming. Consequently, implementing an accurate in-situ defects inspection system in the production environment is even more challenging, since the requirements on positioning, fast measurement, long term stability and robustness against environmental disturbance are demanding. For in-situ R2R defects inspection systems the following conditions need to be satisfied by the inspection tools. Firstly the measurement must be fast and have no physical contact with the inspected film surface. Secondly the measurement system must be robust against the environmental disturbance inspection. Finally the system should have sub-micrometre lateral resolution and nanometre vertical resolution in order to be able to distinguish defects on the film surface. Optical interferometry techniques have the potentially to be used as a solution for such application. However they are extremely sensitive to environmental noise such as mechanical vibration, air turbulence and temperature drift. George [2] reported that a single shot interferometry system “FlexCam” developed by 4D Technology being used currently to detect defects for PV barrier films manufactured by R2R technology. It is robust against environmental disturbances; but it has a limited vertical range, which is restricted by the phase ambiguity of the phase shift interferometry. This vertical measurement range (a few hundreds nanometres) is far less than the normal vertical range of defects (a few micrometres up to a few tens micrometres). It is not possible to detect the majority of defects in the R2R flexible PV barrier films

Evaluating Visual Odometry Methods for Autonomous Driving in Rain

The increasing demand for autonomous vehicles has created a need for robust navigation systems that can also operate effectively in adverse weather conditions. Visual odometry is a technique used in these navigation systems, enabling the estimation of vehicle position and motion using input from onboard cameras. However, visual odometry accuracy can be significantly impacted in challenging weather conditions, such as heavy rain, snow, or fog. In this paper, we evaluate a range of visual odometry methods, including our DROIDSLAM based heuristic approach. Specifically, these algorithms are tested on both clear and rainy weather urban driving data to evaluate their robustness. We compiled a dataset comprising of a range of rainy weather conditions from different cities. This includes, the Oxford Robotcar dataset from Oxford, the 4Seasons dataset from Munich and an internal dataset collected in Singapore. We evaluated different visual odometry algorithms for both monocular and stereo camera setups using the Absolute Trajectory Error (ATE). Our evaluation suggests that the Depth and Flow for Visual Odometry (DF-VO) algorithm with monocular setup worked well for short range distances (< 500m) and our proposed DROID-SLAM based heuristic approach for the stereo setup performed relatively well for long-term localization. Both algorithms performed consistently well across all rain conditions.Comment: 8 pages, 4 figures, Accepted at IEEE International Conference on Automation Science and Engineering (CASE) 202

On the development of the convective boundary layer in a shear-free thermally forced stably stratified fluid setting: a 2D and 3D experimental investigation using image analysis techniques coupled with temperature measurements

The motion of buoyancy driven plumes is, on all scales, the most common heat and momentum transfer mechanism in geophysical flows, well known as Free Convection. Similarly, density stratification due to heating inequalities is also an ordinary scenario in nature. Free Convection phenomenon coupled with a density stratified fluid setting leads to the so-called Penetrative Free Convection (PFC). When a fluid, in static equilibrium, is stably stratified a thermal forcing can produce an unstable configuration ensuing internal waves formation of increasing amplitude. If the perturbation is strong enough, it can definitely erode the initial stratification and cause the motion of turbulent buoyant updrafts, dome-shaped, compensated by denser downdrafts. The entrainment phenomenon occurring at the interface between the turbulent and non-turbulent region justifies the penetrative feature of convection and causes the non linear growth of the Convective Boundary Layer (CBL) of well mixed fluid against the adjacent stably stratified region. In addition to the wide engineering applications, the environmental impact mostly motivates PFC studies. The upper lakes and oceans, under calm conditions, usually exhibit a continuous, moderately stable density distribution. Turbulent convective flow can be generated both by the free-surface cooling and wind shear-stress, eroding the stable stratification on a daily or seasonal time scale. Domes with large downward velocities are generated at the free surface, balanced by updrafts with lower velocity but larger area. Because of the relatively rapid mixing, the density distribution is approximately uniform in the upper layer and it deepens with time as a result of the entrainment and erosion of the underlying denser water. An analogous phenomenon is observed in the lower troposphere when surface heating due to solar radiation results in a growing unstable layer adjacent to the ground which replaces a nocturnal inversion from below. In this case, the initially stable environment near the ground is affected by convection characterized by relatively narrow and fast plumes of rising horizontal surfaces balanced by larger regions of downward slower motion. Resulting internal waves generated within the stable layer take place at or below the Brunt-Väisälä frequency, which is related to the vertical temperature gradient. In nature, the dynamics of the CBL influences the transport and mixing features of a given stratified fluid-body. The amount of materials being mixed due to penetrative convection is a crucial issue both in water or air quality monitoring and forecast with important implications in environmentally-friendly studies. Focusing on the environmental aspect, the pollutant dispersion is a matter of particular importance. On one hand, mixing processes inside the CBL help increasing dispersion with some positive consequences: the concentration of potential harmful pollutants in high risk zones tends to decrease, the turnover and the redistribution of vital substances, like oxygen and nutrients, is guaranteed; the latter plays a major role in large water bodies. These advantages are essential for the safety of populations living close to urban or industrial areas, or for preserving coastal human activities and ecosystems. On the other hand each pollutant, released inside the CBL mainly by human activities, remains confined inside it because of the interface with the non-turbulent region, which acts as a barrier for outward transport. Considering the proximity of the CBL with biosphere, a deeper insight into dispersion and entrainment processes appears mandatory either for sustainable engineering design or for monitoring purposes. Given the great applicability of the topic in several scientific and engineering fields, large amount of experimental, theoretical and numerical investigations on CBL development in a continuously and linearly stratified fluid setting had been conducted in the past since sixties. It appears there is a lack of consensus about the dependence of integral parameters of convective entrainment (in particular the CBL growth rate) on the initial stratification strength and convective phenomenon evolution. Driven by all these premises the main aims of the present research are related to better understanding dispersion of a passive scalar inside the CBL with a lagrangian, non-local approach and a fully three-dimensional (3D 3C) experimental technique, which for the first time has been applied to the topic. When turbulent convection occurs, in fact, dispersion is mostly due to transport by large organized structures while molecular diffusion can be neglected. Given this assumption, a non local approach based on a fully advective-like behaviour of the tracer is necessary and a lagrangian description of flow may be more suitable. Moreover, the knowledge of the horizontal and vertical extension of the structures dominating the flow field appears to be mandatory. Furthermore, turbulence is fully three-dimensional on the scales of motion characterising the phenomena in nature. In order to better understanding and likely describing the evolution of turbulent structures inside the convective layer, a three dimensional experimental technique is strongly required. In the present work shear free convection experiments in a stably stratified environment were performed in a thermally controlled convection chamber. The experimental set up was arranged in different optical configurations to ensure the two components and three components of velocity to be measured in an illuminated plane and volume respectively through different image analysis techniques with sub-pixel accuracy. Temperature measurements were simultaneously acquired using thermocouples of accuracy less than 0.1 °C. The experiments highlighted the time evolution of the convective structure characteristic spatial scales (CBL height and horizontal spacing between thermals) and the non local description of transport and mixing inside the growing CBL. The main novelty of the present contribution covers the improvement of techniques and methods to achieve more reliable, statistically robust and likely results. The experimental effort based on image analysis techniques (mainly Feature Tracking and photogrammetric 3D-PTV) resulted suitable for reconstructing longer trajectories (always more than 103 trajectories longer than 20 consecutive snapshots) and analyzing larger particle density images (reliable results for more than 2000 particles in a volume of 15X15X15 cm3 for 3D-PTV). Velocity statistics are then more robust than those from classical Particle Tracking Velocimetry. Moreover, for the first time, a fully three-dimensional particle tracking technique has been applied to penetrative convection experiments. 3D-PTV allows a more realistic description of the velocity field, which occurs during the evolution of the convective mixed layer, than more traditional 2D techniques. Furthermore, photogrammetric 3D-PTV rather than “scanning” 3D-PTV results in more accuracy when the tracer particle density is high, because particles may be tracked directly in the 3D space rather than through matching of 2D projections. The broader impact of the research mainly refers to the prediction of the CBL growth as a function of initial and boundary conditions with better accuracy than conventional and well established techniques. The experimental study can thus give a positive contribution on real pollutant dispersion studies in urban and natural environments for environmental protection and sustainable design purposes. Field experiments aimed at measuring the turbulence budget of the CBL have shown that the mechanical generation of kinetic energy by wind shear is often confined close to the heat source supporting the validity of laboratory models in which no wind is present. According to this assumption, the similarity proposed by Deardorff (1970) is employed to compute scaling parameters and to make results comparable with real scales. Through normalizing the quantities measured at different stages of the experiment, the phenomenon can be considered as a succession of steady states, according to an evolution of the variables of interest that may be defined quasi-steady state. The experimental apparatus employed to run the experiments is the same as in Cenedese and Querzoli (1994), Querzoli (1996), Cenedese and Querzoli (1997) and Moroni and Cenedese (2006). The spatial resolution of velocity data is largely increased here by means of 2D and 3D image analysis techniques (Feature Tracking, FT, and 3D Particle Tracking Velocimetry, 3D-PTV) used instead of Laser-Doppler Anemometry or 2D Particle Tracking Velocimetry as in Cenedese and Querzoli, 1994; Querzoli, 1996 and Cenedese and Querzoli, 1997. Moreover the photogrammetric 3D-PTV here applied allows fully three-dimensional descriptions of both the Eulerian velocity field and Lagrangian particle trajectories for a more likely understanding of the phenomenon than through the 2D approach used in Moroni and Cenedese (2006). Furthermore, the combined use of thermocouples and flow visualization techniques allows cross-validating different methods to estimate the evolutions of the key parameters and the plume characteristic dimensions. Two different experimental arrangements were set-up, 2D and a 3D models. A large set of data were firstly acquired using a 2D model and employing FT. The preliminary investigation was mainly focused on better understanding the physics of the phenomenon, finding a time scaling law, testing different methods to compute the variables of interest and comparing results with classical methods found in literature. When 2D techniques are employed to detect the velocity field, the flow is illuminated with a thin light sheet and only the velocity components within this sheet can be evaluated. Driven by the idea that only a fully three-dimensional technique can significantly improve our laboratory model in term of a more likely description of free convection structures we run a second set of experiments, by using a stereoscopic arrangement of cameras focused on an illuminated volume. Although some methods do exist for reconstructing 3D velocities in a point (3D laser Doppler Anemometry; Hinsch and Hinrichs, 1996) or plane (3D stereo-PIV; Stuer et al., 1999), only a fully 3D technique based on the illumination of a flow volume rather than a flow sheet will give the information needed to construct the instantaneous 3D velocity fields. A number of imaging-based measurement techniques exist for determining 3D velocity fields in an observation volume. Among these are: scanning, photogrammetric, holographic or photogrammetric techniques dependending on which principle is recalled to reconstruct the third dimension from a 2D image/s: The present study was focused on 3D-PTV which is a 3D extension of the 2D particle-tracking methods. 3D-PTV is based on reconstructing 3D trajectories of reflecting tracer particles through a photogrammetric recording of image sequences. The 3D particle trajectories obtained can be used to calculate the 3D velocity field. The 3D-PTV optical system has been designed with the following capabilities: image a volume far away the boundary walls, lengthen the trajectories, and improve the accuracy of the procedure through a careful test on synthetically generated data. A physically-based photogrammetric calibration of the stereoscopic arrangement was employed and its accuracy tested. The effects of multimedia geometry on calibration parameters were taken into account. The combination of image- and object-space based information was employed to establish the correspondences between particle positions (structure from stereo reconstruction). A particle tracking algorithm was then employed to reconstructed 3D trajectories. Sensitivity tests conducted on the matching algorithm proved that the calibration accuracy is fundamental to obtain the correct matching and particle tracking; small errors in calibration parameters or neglecting water refraction effects reduce matching performance. On the other hand, accuracy less than 1 pixel was reached with our calibration procedure ensuring good results in the matching procedure. Tests on synthetic data demonstrated a multi-choice strategy with a 3 camera arrangement is the best solution for matching data. It is less sensitive to errors in the calibration data set when both the percentage of correctly matched triplets and the number of outputs of the algorithm were considered. Original and cross-validating methods to compute the CBL height and horizontal scale of thermals were applied based on temperature, velocity and fluorescence imaging. The spatial covariance of the velocity field, providing the plume horizontal spacing, allows the spatial extension of the mixed region to be determined. Dome characteristic vertical dimension is of the same order of magnitude as the mixing layer height, while their horizontal dimension becomes similar to the vertical one at the end of the experiment when the structure dimensions are comparable to the test section side and border effects are no longer negligible. The mixing layer growth was computed by exploiting both temperature and velocity data. Outputs were then compared to more classical methods as the zero-order mixed-layer model and the zero-heat flux level method. The accuracy of our methods was computed as well. Present results, normalized accordingly to the Deardorff similarity for free convection, were compared with literature data and LES meteorological models. Outcomes from different experimental configurations, literature and LES models are in fairly good agreement. The comparison with literature data at real scale demonstrates the validity of our experimental task and its applicability for the study of the real atmospheric boundary layer and its monitoring for environmental purposes. On the other hand the agreement with LES models at different boundary conditions and domain aspect ratios proves that both scale and border effects of the experimental model are negligible if data are not processed for too long time

On the development of the convective boundary layer in a shear-free thermally forced stably stratified fluid setting: a 2D and 3D experimental investigation using image analysis techniques coupled with temperature measurements

The motion of buoyancy driven plumes is, on all scales, the most common heat and momentum transfer mechanism in geophysical flows, well known as Free Convection. Similarly, density stratification due to heating inequalities is also an ordinary scenario in nature. Free Convection phenomenon coupled with a density stratified fluid setting leads to the so-called Penetrative Free Convection (PFC). When a fluid, in static equilibrium, is stably stratified a thermal forcing can produce an unstable configuration ensuing internal waves formation of increasing amplitude. If the perturbation is strong enough, it can definitely erode the initial stratification and cause the motion of turbulent buoyant updrafts, dome-shaped, compensated by denser downdrafts. The entrainment phenomenon occurring at the interface between the turbulent and non-turbulent region justifies the penetrative feature of convection and causes the non linear growth of the Convective Boundary Layer (CBL) of well mixed fluid against the adjacent stably stratified region. In addition to the wide engineering applications, the environmental impact mostly motivates PFC studies. The upper lakes and oceans, under calm conditions, usually exhibit a continuous, moderately stable density distribution. Turbulent convective flow can be generated both by the free-surface cooling and wind shear-stress, eroding the stable stratification on a daily or seasonal time scale. Domes with large downward velocities are generated at the free surface, balanced by updrafts with lower velocity but larger area. Because of the relatively rapid mixing, the density distribution is approximately uniform in the upper layer and it deepens with time as a result of the entrainment and erosion of the underlying denser water. An analogous phenomenon is observed in the lower troposphere when surface heating due to solar radiation results in a growing unstable layer adjacent to the ground which replaces a nocturnal inversion from below. In this case, the initially stable environment near the ground is affected by convection characterized by relatively narrow and fast plumes of rising horizontal surfaces balanced by larger regions of downward slower motion. Resulting internal waves generated within the stable layer take place at or below the Brunt-Väisälä frequency, which is related to the vertical temperature gradient. In nature, the dynamics of the CBL influences the transport and mixing features of a given stratified fluid-body. The amount of materials being mixed due to penetrative convection is a crucial issue both in water or air quality monitoring and forecast with important implications in environmentally-friendly studies. Focusing on the environmental aspect, the pollutant dispersion is a matter of particular importance. On one hand, mixing processes inside the CBL help increasing dispersion with some positive consequences: the concentration of potential harmful pollutants in high risk zones tends to decrease, the turnover and the redistribution of vital substances, like oxygen and nutrients, is guaranteed; the latter plays a major role in large water bodies. These advantages are essential for the safety of populations living close to urban or industrial areas, or for preserving coastal human activities and ecosystems. On the other hand each pollutant, released inside the CBL mainly by human activities, remains confined inside it because of the interface with the non-turbulent region, which acts as a barrier for outward transport. Considering the proximity of the CBL with biosphere, a deeper insight into dispersion and entrainment processes appears mandatory either for sustainable engineering design or for monitoring purposes. Given the great applicability of the topic in several scientific and engineering fields, large amount of experimental, theoretical and numerical investigations on CBL development in a continuously and linearly stratified fluid setting had been conducted in the past since sixties. It appears there is a lack of consensus about the dependence of integral parameters of convective entrainment (in particular the CBL growth rate) on the initial stratification strength and convective phenomenon evolution. Driven by all these premises the main aims of the present research are related to better understanding dispersion of a passive scalar inside the CBL with a lagrangian, non-local approach and a fully three-dimensional (3D 3C) experimental technique, which for the first time has been applied to the topic. When turbulent convection occurs, in fact, dispersion is mostly due to transport by large organized structures while molecular diffusion can be neglected. Given this assumption, a non local approach based on a fully advective-like behaviour of the tracer is necessary and a lagrangian description of flow may be more suitable. Moreover, the knowledge of the horizontal and vertical extension of the structures dominating the flow field appears to be mandatory. Furthermore, turbulence is fully three-dimensional on the scales of motion characterising the phenomena in nature. In order to better understanding and likely describing the evolution of turbulent structures inside the convective layer, a three dimensional experimental technique is strongly required. In the present work shear free convection experiments in a stably stratified environment were performed in a thermally controlled convection chamber. The experimental set up was arranged in different optical configurations to ensure the two components and three components of velocity to be measured in an illuminated plane and volume respectively through different image analysis techniques with sub-pixel accuracy. Temperature measurements were simultaneously acquired using thermocouples of accuracy less than 0.1 °C. The experiments highlighted the time evolution of the convective structure characteristic spatial scales (CBL height and horizontal spacing between thermals) and the non local description of transport and mixing inside the growing CBL. The main novelty of the present contribution covers the improvement of techniques and methods to achieve more reliable, statistically robust and likely results. The experimental effort based on image analysis techniques (mainly Feature Tracking and photogrammetric 3D-PTV) resulted suitable for reconstructing longer trajectories (always more than 103 trajectories longer than 20 consecutive snapshots) and analyzing larger particle density images (reliable results for more than 2000 particles in a volume of 15X15X15 cm3 for 3D-PTV). Velocity statistics are then more robust than those from classical Particle Tracking Velocimetry. Moreover, for the first time, a fully three-dimensional particle tracking technique has been applied to penetrative convection experiments. 3D-PTV allows a more realistic description of the velocity field, which occurs during the evolution of the convective mixed layer, than more traditional 2D techniques. Furthermore, photogrammetric 3D-PTV rather than “scanning” 3D-PTV results in more accuracy when the tracer particle density is high, because particles may be tracked directly in the 3D space rather than through matching of 2D projections. The broader impact of the research mainly refers to the prediction of the CBL growth as a function of initial and boundary conditions with better accuracy than conventional and well established techniques. The experimental study can thus give a positive contribution on real pollutant dispersion studies in urban and natural environments for environmental protection and sustainable design purposes. Field experiments aimed at measuring the turbulence budget of the CBL have shown that the mechanical generation of kinetic energy by wind shear is often confined close to the heat source supporting the validity of laboratory models in which no wind is present. According to this assumption, the similarity proposed by Deardorff (1970) is employed to compute scaling parameters and to make results comparable with real scales. Through normalizing the quantities measured at different stages of the experiment, the phenomenon can be considered as a succession of steady states, according to an evolution of the variables of interest that may be defined quasi-steady state. The experimental apparatus employed to run the experiments is the same as in Cenedese and Querzoli (1994), Querzoli (1996), Cenedese and Querzoli (1997) and Moroni and Cenedese (2006). The spatial resolution of velocity data is largely increased here by means of 2D and 3D image analysis techniques (Feature Tracking, FT, and 3D Particle Tracking Velocimetry, 3D-PTV) used instead of Laser-Doppler Anemometry or 2D Particle Tracking Velocimetry as in Cenedese and Querzoli, 1994; Querzoli, 1996 and Cenedese and Querzoli, 1997. Moreover the photogrammetric 3D-PTV here applied allows fully three-dimensional descriptions of both the Eulerian velocity field and Lagrangian particle trajectories for a more likely understanding of the phenomenon than through the 2D approach used in Moroni and Cenedese (2006). Furthermore, the combined use of thermocouples and flow visualization techniques allows cross-validating different methods to estimate the evolutions of the key parameters and the plume characteristic dimensions. Two different experimental arrangements were set-up, 2D and a 3D models. A large set of data were firstly acquired using a 2D model and employing FT. The preliminary investigation was mainly focused on better understanding the physics of the phenomenon, finding a time scaling law, testing different methods to compute the variables of interest and comparing results with classical methods found in literature. When 2D techniques are employed to detect the velocity field, the flow is illuminated with a thin light sheet and only the velocity components within this sheet can be evaluated. Driven by the idea that only a fully three-dimensional technique can significantly improve our laboratory model in term of a more likely description of free convection structures we run a second set of experiments, by using a stereoscopic arrangement of cameras focused on an illuminated volume. Although some methods do exist for reconstructing 3D velocities in a point (3D laser Doppler Anemometry; Hinsch and Hinrichs, 1996) or plane (3D stereo-PIV; Stuer et al., 1999), only a fully 3D technique based on the illumination of a flow volume rather than a flow sheet will give the information needed to construct the instantaneous 3D velocity fields. A number of imaging-based measurement techniques exist for determining 3D velocity fields in an observation volume. Among these are: scanning, photogrammetric, holographic or photogrammetric techniques dependending on which principle is recalled to reconstruct the third dimension from a 2D image/s: The present study was focused on 3D-PTV which is a 3D extension of the 2D particle-tracking methods. 3D-PTV is based on reconstructing 3D trajectories of reflecting tracer particles through a photogrammetric recording of image sequences. The 3D particle trajectories obtained can be used to calculate the 3D velocity field. The 3D-PTV optical system has been designed with the following capabilities: image a volume far away the boundary walls, lengthen the trajectories, and improve the accuracy of the procedure through a careful test on synthetically generated data. A physically-based photogrammetric calibration of the stereoscopic arrangement was employed and its accuracy tested. The effects of multimedia geometry on calibration parameters were taken into account. The combination of image- and object-space based information was employed to establish the correspondences between particle positions (structure from stereo reconstruction). A particle tracking algorithm was then employed to reconstructed 3D trajectories. Sensitivity tests conducted on the matching algorithm proved that the calibration accuracy is fundamental to obtain the correct matching and particle tracking; small errors in calibration parameters or neglecting water refraction effects reduce matching performance. On the other hand, accuracy less than 1 pixel was reached with our calibration procedure ensuring good results in the matching procedure. Tests on synthetic data demonstrated a multi-choice strategy with a 3 camera arrangement is the best solution for matching data. It is less sensitive to errors in the calibration data set when both the percentage of correctly matched triplets and the number of outputs of the algorithm were considered. Original and cross-validating methods to compute the CBL height and horizontal scale of thermals were applied based on temperature, velocity and fluorescence imaging. The spatial covariance of the velocity field, providing the plume horizontal spacing, allows the spatial extension of the mixed region to be determined. Dome characteristic vertical dimension is of the same order of magnitude as the mixing layer height, while their horizontal dimension becomes similar to the vertical one at the end of the experiment when the structure dimensions are comparable to the test section side and border effects are no longer negligible. The mixing layer growth was computed by exploiting both temperature and velocity data. Outputs were then compared to more classical methods as the zero-order mixed-layer model and the zero-heat flux level method. The accuracy of our methods was computed as well. Present results, normalized accordingly to the Deardorff similarity for free convection, were compared with literature data and LES meteorological models. Outcomes from different experimental configurations, literature and LES models are in fairly good agreement. The comparison with literature data at real scale demonstrates the validity of our experimental task and its applicability for the study of the real atmospheric boundary layer and its monitoring for environmental purposes. On the other hand the agreement with LES models at different boundary conditions and domain aspect ratios proves that both scale and border effects of the experimental model are negligible if data are not processed for too long time