This paper considers the attitude determination problem of a three-vehicle heterogeneous formation, whose line of sight is constrained. By some reason, such as large distance, two of the vehicles, the deputies, cannot measure the direction of each other's position. The deputies can only measure the relative direction relative to the chief, which is the remaining vehicle in the formation. The special cases of the problem are described in terms of the number of solutions related to each configuration. In general, there is only one solution, but infinite or even two ambiguous solutions are possible, respectively in the degenerate and ambiguous configurations. These arise due to lack of information or symmetry in the data, respectively. Furthermore, the subset of special configurations is a zero measure set of the global set of configurations, which is an important property of the problem. Simulations that test and validate the described configurations are shown as well, which also help to understand what effects the quality of the solution obtained according to a special case proximity metric.

This paper addresses a new attitude determination problem for formations. It considers a three-vehicle formation with relative and inertial measurements from sensors, where Constraints limit the relative measurements, which are not available between two of the vehicles, also known as deputies. The other vehicle is called the chief and does not have any limitation. Furthermore, each of the vehicles has an independent inertial measurement, whose references are known. The goal is to determine all attitude relations, both inertial and relative. The solution for this problem is divided into different stages. First, the relative attitude between the chief and the deputies is assessed, which results in two candidates for each of these relations. Then, each candidate yields a candidate for the inertial attitude of the chief. Next, comparing the four inertial candidates gives the solution for their respective relations and consequently for the relative relations as well. The remaining relations derive directly from those already known. The paper also provides some early insights about degeneracies, possible particular cases of the solution, and the effect of sensor noise. Finally, the solution is validated with a simulation, whose results are similar to attitude determination problems in constrained formations.

This paper presents a localization solution for the study of tagged marine animals (sources) based on direction and Doppler measurements. The source localization, in 3-D, is supported by a Portable Underwater Robotic Tool (PURT), comprising a Ultra-Short Baseline (USBL) aided INS navigation system, carried by a diver (agent). Furthermore, a Surface Robotic Tool (SRT) provides the agent with its absolute position expressed in inertial coordinates. The observability of the system is studied and realistic simulation results are presented, in the presence of measurement noise.

This paper presents the design, analysis, and experimental validation of a globally asymptotically stable (GAS) filter for simultaneous localization and mapping (SLAM), with application to unmanned aerial vehicles. The SLAM problem is formulated in a sensor-based framework and modified in such a way that the underlying system structure can be regarded as linear time varying for observability analysis and filter design purposes, from which a linear Kalman filter with GAS error dynamics follows naturally. The performance and consistency validation of the proposed sensor-based SLAM filter are successfully assessed with real data, acquired indoors, using an instrumented quadrotor.

This paper proposes novel cooperative navigation solutions for an Intervention Autonomous Underwater Vehicle (I-AUV) working in tandem with an Autonomous Surface Craft (ASC). The I-AUV is assumed to be moving in the presence of constant unknown ocean currents, and aims to estimate its position relying on measurements of its range to the ASC and of its depth relatively to the sea level. Two different scenarios are considered: in one, the ASC transmits its position and velocity to the I-AUV, while in the other the ASC transmits only its position, and the I-AUV has access to measurements of its velocity relative to the ASC. A sufficient condition for observability and a method for designing state observers with Globally Asymptotically Stable (GAS) error dynamics are presented for both problems. Finally, simulation results are included and discussed to assess the performance of the proposed solutions in the presence of measurement noise.

This paper presents the design and performance evaluation of a low-cost Attitude and Heading Reference System (AHRS) for autonomous vehicles. A single sensor pack, an Inertial Measurement Unit (IMU), provides all the data required to feed the attitude filter. The design is sensor-driven and departs from traditional solutions as no explicit representations of the attitude, e.g., Euler angles, quaternions, or rotation matrices, are considered in the filter design. Moreover, the proposed solution includes the estimation of rate gyros biases, systematic tuning procedures, and also allows for the inclusion of frequency weights to model colored noise on the different sensor channels. Due to its inherent structure, the filter is complementary, allows for temporary loss of sensor measurements, and also copes well with slowly time-varying rate gyros biases. The performance of the proposed algorithm is experimentally evaluated with a low-cost IMU and resorting to a high precision calibration table, which provides ground truth signals for comparison with the resulting filter estimates.

A new sensor-based homing integrated guidance and control law is presented to drive an underactuated autonomous underwater vehicle (AUV) toward a fixed target, in three dimensions, using the information provided by an ultrashort baseline (USBL) positioning system. The guidance and control law is first derived using quaternions to express the vehicle's attitude kinematics, which are directly obtained from the time differences of arrival (TDOA) measured by the USBL sensor. The dynamics are then included resorting to backstepping techniques. The proposed Lyapunov-based control law yields global asymptotic stability in the absence of external disturbances and is further extended, keeping the same properties, to the case where constant known ocean currents affect the dynamics of the vehicle. Finally, a globally exponentially stable nonlinear TDOA and range-based observer is introduced to estimate the ocean current and uniform asymptotic stability is obtained for the overall closed-loop system. Simulations are presented illustrating the performance of the proposed solutions.