Characterization of optical communication in a leader-follower unmanned underwater vehicle formation

As part of the research to development an optical communication design of a leader-follower formation between unmanned underwater vehicles (UUVs), this paper presents light field characterization and design configuration of the hardware required to allow the use of distance detection between UUVs. The study specifically is targeting communication between remotely operated vehicles (ROVs). As an initial step in this study, the light field produced from a light source mounted on the leader UUV was empirically characterized and modeled. Based on the light field measurements, a photo-detector array for the follower UUV was designed. Evaluation of the communication algorithms to monitor the UUV’s motion was conducted through underwater experiments in the Ocean Engineering Laboratory at the University of New Hampshire. The optimal spectral range was determined based on the calculation of the diffuse attenuation coefficients by using two different light sources and a spectrometer. The range between the leader and the follower vehicles for a specific water type was determined. In addition, the array design and the communication algorithms were modified according to the results from the light field

Determination of some heavy metals in imported rice grains (Oryza sativa) available in Sulaymaniyah market and evaluation of their health risk assessment

This investigation was conducted to assess the levels of some heavy metals such as arsenic, lead, cadmium, chromium, copper, zinc, iron, nickel, and manganese in imported rice sold on the Sulaymaniyah market – Iraqi Kurdistan. The potential human health risk assessment was conducted by considering estimated weekly intake (EWI) of heavy metals from eating rice and calculated values compared with provisional tolerable weekly intake (PTWI). The mean values for copper, manganese and zinc were considerably higher than allowable limits set by FAO/WHO. While the lead value in the entire rice types were lower than allowable limits set by FAO/WHO except (Uruguayan rice R9 and R12, Iranian rice R20, American rice R24, and Russian rice R26). The concentration of iron and nickel in some rice brands were less than the standard limit, and the chromium value was within the safe limit except for these (Indian rice R1, Uruguayan rice R12, Iranian rice R20, Chinese rice R33) brands, which were higher than the acceptable limit. EWI for chromium and nickel in most samples were higher than the PTWI. Also, EWI for zinc, manganese, and copper was higher than the PTWI set by FAO/WHO. Moreover, the EWI for lead were considerably higher than other measured toxic metals, and the highest mean level of EWI for lead was observed in some imported rice samples. Thus, the high consumption of rice contaminated with heavy metals can cause potential health risks to the Kurdish population in Kurdistan. More consideration should be given to contaminated rice and prevention and control measures should be taken

High-Resolution Vertical Habitat Mapping of a Deep-Sea Cliff Offshore Greenland

Recent advances in deep-sea exploration with underwater vehicles have led to the discovery of vertical environments inhabited by a diverse sessile fauna. However, despite their ecological importance, vertical habitats remain poorly characterized by conventional downward-looking survey techniques. Here we present a high-resolution 3-dimensional habitat map of a vertical cliff hosting a suspension-feeding community at the flank of an underwater glacial trough in the Greenland waters of the Labrador Sea. Using a forward-looking set-up on a Remotely Operated Vehicle (ROV), a high-resolution multibeam echosounder was used to map out the topography of the deep-sea terrain, including, for the first time, the backscatter intensity. Navigational accuracy was improved through a combination of the USBL and the DVL navigation of the ROV. Multi-scale terrain descriptors were derived and assigned to the 3D point cloud of the terrain. Following an unsupervised habitat mapping approach, the application of a K-means clustering revealed four potential habitat types, driven by geomorphology, backscatter and fine-scale features. Using groundtruthing seabed images, the ecological significance of the four habitat clusters was assessed in order to evaluate the benefit of unsupervised habitat mapping for further fine-scale ecological studies of vertical environments. This study demonstrates the importance of a priori knowledge of the terrain around habitats that are rarely explored for ecological investigations. It also emphasizes the importance of remote characterization of habitat distribution for assessing the representativeness of benthic faunal studies often constrained by time-limited sampling activities. This case study further identifies current limitations (e.g., navigation accuracy, irregular terrain acquisition difficulties) that can potentially limit the use of deep-sea terrain models for fine-scale investigations

Sistema de Localização Subaquático para Veículos Autónomos

A necessidade de exploração e mineração no meio subaquático desencadeou, de alguma forma, uma acentuada evolução nas tecnologias e no desenvolvimento de veículos autónomos que opere nesse tipo de ambientes. A autonomia nas operações encontra-se, inteiramente, relacionada com o sistema de localização e é nesse sentido que o desenvolvimento desta dissertação se foca. Os resultados obtidos com o presente estudo pretendem constituir um contributo para a obtenção de maior precisão e exatidão na performance de um sistema de localização subaquático. Neste sentido, são estudados dois aspetos fundamentais para um sistema de localização ser robusto e preciso, sendo eles a fusão sensorial e a calibração. A fusão sensorial consistiu em utilizar um EKF com dados sensoriais do DVL, USBL, acelerómetros e sensor de pressão para estimar a localização. No entanto, para a realização da fusão sensorial, os sensores necessitam de ser calibrados, pois o desalinhamento entre os diversos sensores produz influência negativamente no sistema de localização. Assim sendo, foi desenvolvido um sistema de calibração para minimizar esse problema. As Minas subaquáticas, é um dos principais locais de operação para UUV para o INESC TEC, no entanto, as Minas apresentam distorções magnéticas sendo uma grande dificuldade para os sistemas de localização tradicionais. Deste modo, foi proposto um modelo para a obtenção da atitude sem recurso aos magnetómetros evitando a essas distorções. Por fim, com o intuito de efetuar a validação dos algoritmos desenvolvidos foram realizados datasets para comprovar a eficiência do sistema de localização subaquático proposto. Os resultados obtidos com o sistema desenvolvido neste estudo, quando comparados com o ground truth apresentaram erros inferiores a meio metro na posição estimada e 0.1 graus na orientação estimada, ao longo de um percurso de 722 m com uma duração de 10 minutos. É de salientar que o filtro probabilístico demonstrou-se robusto mesmo com a existência de algumas falhas na obtenção das medidas dos sensores acústicos.The need to explore and mine underwater has triggered, in some ways, a pronounced evolution of the technologies and the development of autonomous vehicles which could operate in that type of environment. The operations autonomy is entirely related with the localization system and this thesis is focused in that sense. The results we obtained with the present study aim to contribute to the process of obtaining a higher precision and accuracy in the performance of an underwater localization system. In this sense, we study two fundamental features for the robustness and precision of a localization system: multiple sensor fusion and system calibration. An Extended Kalman Filter was used to fuse the sensor data from Doppler Velocity Log, Ultra-short baseline, accelerometers and a pressure sensor to estimate the position. However, in order to perform the sensorial fusion, the sensors need to be calibrated since the misalignment between the different sensors produces negative effects on the localization system. Thus, we have developed a calibration system to decimate this problem. The underwater mines, one of the means of operation for the autonomous vehicles used in some ongoing projects at the INESC TEC's Centre for Robotics and Autonomous Systems, present very hostile characteristics with high magnetic distortions. This being the case, we have proposed a model to obtain the attitude without resorting to the magnetometers which would be immune to these distortions. Lastly, in order to validate the algorithms we have developed, we have performed datasets to prove the eficiency of the underwater localization system we propose. The results we obtained with the system we have developed in this study, when compared to the ground truth, presented errors which were inferior to half a meter in the estimated position and 0.1 degrees in the estimated orientation, through a route of 722 meters with a duration of 10 minutes. We should emphasize that the probabilistic filter proved to be robust even with the existence of some aws while obtaining the measurements of the acoustic sensors

Pose Detection and Control of Unmanned Underwater Vehicles (UUVs) Utilizing an Optical Detector Array

As part of the research for development of a leader-follower formation between unmanned underwater vehicles (UUVs), this study presents an optical feedback system for UUV navigation via an optical detector array. Capabilities of pose detection and control in a static-dynamic system (e.g. UUV navigation into a docking station) and a dynamic-dynamic system (e.g. UUV to UUV leader-follower system) are investigated. In both systems, a single light source is utilized as a guiding beacon for a tracker/follower UUV. The UUV uses an optical array consisting of photodiodes to receive the light field emitted from the light source. For UUV navigation applications, accurate pose estimation is essential. In order to evaluate the feasibility of underwater distance detection, the effective communication range between two platforms, i.e. light source and optical detector, and the optimum spectral range that allowed maximum light transmission are calculated. Based on the light attenuation in underwater, the geometry and dimensions of an optical detector array are determined, and the boundary conditions for the developed pose detection algorithms along with the error sources in the experiments are identified. As a test bed to determine optical array dimensions and size, a simulator, i.e. numerical software, is developed, where planar and curved array geometries of varying number of elements are analytically compared and evaluated. Results show that the curved optical detector array is able to distinguish 5 degree- of-freedom (DOF) motion (translation in x, y, z-axes and pitch and yaw rotations) with respect to a single light source. Analytical pose detection and control algorithms are developed for both static-dynamic and dynamic-dynamic systems. Results show that a 5 x 5 curved detector array with the implementation of SMC is reasonably sufficient for practical UUV positioning applications. The capabilities of an optical detector array to determine the pose of a UUV in 3-DOF (x, y and z-axes) are experimentally tested. An experimental platform consisting of a 5 x 5 photodiode array mounted on a hemispherical surface is used to sample the light field emitted from a single light source. Pose detection algorithms are developed to detect pose for steady-state and dynamic cases. Monte Carlo analysis is conducted to assess the pose estimation uncertainty under varying environmental and hardware conditions such as water turbidity, temperature variations in water and electrically-based noise. Monte Carlo analysis results show that the pose uncertainties (within 95% confidence interval) associated with x, y and z-axes are 0.78 m, 0.67 m and 0.56 m, respectively. Experimental results demonstrate that x, y and z-axes pose estimates are accurate to within 0.5 m, 0.2 m and 0.2 m, respectively