Easily Deployable Underwater Acoustic Navigation System for Multi-Vehicle Environmental Sampling Applications

Water as a medium poses a number of challenges for robots, limiting the progress of research in underwater robotics vis-a-vis ground or aerial robotics. The primary challenges are satellite based positioning and radio communication being unusable due to high attenuation of electromagnetic waves in water. We have developed miniature, agile, easy to carry and deploy Autonomous Underwater Vehicles (AUVs) equipped with a suite of sensors for underwater environmental sensing. We previously demonstrated adaptive sampling and feature tracking, and gathered data from a lake for limnological research, with the AUV performing inertial navigation. In this paper, we demonstrate a new underwater acoustic positioning system, which allows on-board estimation of AUV position. Our system uses absolute time information from GNSS for initial clock synchronization and uses one-way-travel-time for range measurements, which makes it scalable in the number of robots. It is easily deployable and does not rely on any installed infrastructure in the environment. We describe various hardware and software components of our system, and present results from experiments in Lake Geneva.

Alexander Bahr, Alcherio Martinoli, Anwar Ahmad Quraishi

IEEE

Real Time Aircraft Position+Attitude of Airborne Sensors

Telmo Cunha, Phillip Tomé

The determination of instantaneous positions with high accuracy using differential GPS techniques is of great importance for several applications, like airborne topographic mapping, airborne gravimetry and altimetry. In some of these applications long baselines are involved creating additional problems in the correct determination of the position of the sensors. The determination of the attitude of the aircraft is also of great importance in this context. This paper presents a technique that, taking advantage of the integration of GPS and inertial measurements, produces real time positions. The demand for real time positioning introduces some more constraints, which must be taken into account from the start of the algorithm development to the end of its implementation. A methodology for processing GPS and raw data from an inertial measurement unit (IMU) was implemented in a feedback integrated structure. The position determination is based on real time DGPS with L1 and L2 carrier phase ambiguity fixing, using on-line IMU processed data to validate and increase the positions reliability, especially during GPS outages and when the aircraft is far away from the nearest GPS reference station. By processing L1 and L2 carrier phase measurements in differential mode between a pair of the aircraft GPS antennas (without resorting to ground reference station data), a partial estimate of the aircraft attitude is obtained. This is critical to align the low cost inertial platform in heading either when the aircraft is stopped or in flight. In addition, the DGPS absolute positions are used to update the IMU data in real time. By using the proposed methodology it was possible to explore the entire potential of a low cost IMU/GPS system. The position and attitude values are obtained from all the measurements through an extended Kalman filter. Decimeter accuracy was achieved for the positions. For the orientation of the aircraft an accuracy of 0.01º (1) for roll and pitch and 0.1º (1 sigma) for heading was achieved. The performance and the results obtained with this system using data from an airborne campaign that took place in Portugal are discussed.

1999

Sensor-Augmented EGNOS/Galileo Receiver for Handheld Applications in Urban and Indoor Environments - SARHA

Phillip Tomé, Okan Yalak

In pedestrian user environments, like dense urban canyons or indoors, the GNSS positioning performance regarding accuracy and availability reaches well-known technological limits. These limitations can be overcome by adding additional sources of information to the system. The main objective of the project ‘SARHA - Sensor-Augmented EGNOS/Galileo Receiver for Handheld Applications in Urban and Indoor Environments’ is the combination of a modern satellite navigation receiver with augmentation and autonomous sensors. Additionally, the hybrid navigation system will be enhanced by a transponder receiver, which communicates with transmitters installed inside buildings, to provide absolute position updates. The transponder will allow the SARHA system to significantly increase reliability and accuracy of the positioning solutions indoors. The hybrid navigation software is split up into two parts. The first one will be implemented directly on the GPS receiver, whereas the second part will run on a microcontroller. In this way a small, low-performance microcontroller can be used, what represents the first step to reduce dimension, weight and energy consumption of the mobile system. The project aims at meeting the requirements of fire fighters, rescue services, police, special task forces, solitary, and lone workers for handheld applications acting in environments with unfavourable satellite signal conditions, using hybrid navigation system architecture. Based on the Galileo signal definitions, analyses are set up to explore the signal characteristics in comparison to the GPS signals. Improvements due to Galileo signal availability in urban and indoor environments are assessed and will later ensure seamless integration of enhanced technologies into continuous developments.

2006

Real Time Aircraft Position+Attitude of Airborne Sensors

Telmo Cunha, Phillip Tomé

1999