Abstract
This work addresses the implementation of the navigation, guidance and control of autonomous underwater vehicles on mobile acoustic networks. After a theoretical discussion of the algorithms required for such operation, we present results from simulation and real experiments that validate the proposed solutions.

Abstract
High frequency synthetic aperture sonar systems require demanding tolerances in motion errors and medium phase stability. This article proposes a new method that mitigates the problems associated with small wavelength related errors. By dividing the received signal bandwidths in to several smaller ones and conjugate complex multiplying them, a new signal is obtained with longer effective wavelength, thus reducing the impact of motion errors and medium phase fluctuations.

Abstract
A new approach for synthetic aperture image formation is presented in this paper. With the presented method image formation is regarded as a signal arrangement that can be described by a matrix. This method integrates the sonar platform motion in the image formation process but more importantly it acknowledges the non ideal data gathering process and implements means to mitigate these shortcomings. This method is illustrated with real data obtained in test mission in the Douro River, Portugal by a synthetic aperture sonar developed at the University of Porto.

Abstract
This work addresses the coordinated operation of an autonomous underwater vehicle and an autonomous surface vessel and its main goal is the development of an infrastructure that allows the surface vessel to dynamically position itself above the underwater vehicle while the later one is collecting data and navigating in long baseline mode using a set of beacons installed in the operation area. Besides a formal statement of the coordination problem, we present results both from real experiments and from simulations that illustrate the proposed solution.

Abstract
This paper describes a Synthetic Aperture Sonar (SAS) system being developed at the University of Porto to be used in a small autonomous boat for the survey of shallow water environments, such as rivers, deltas, estuaries and dams. Its purpose is to obtain high resolution echo reflectivity maps through synthetic aperture techniques, taking advantage of the high precision navigation system of the boat. In the future the production of bottom tomography maps is also considered through the use of interferometric imaging techniques.

Abstract
In this paper we describe an algorithm that produces a post mission estimate of the spatial evolution of the Isurus AUV. To make this post processing possible, the navigation system records on the vehicle logging system all the navigation data received during the mission execution. The data comprise the depth of the vehicle, the outputs of the tilt sensors and digital compass, the angular velocity of the propeller, as well as acoustic range measurements to a set of transponders. After mission completion, the logged data is then processed to produce the estimate of the evolution of the vehicle. The algorithm used to process this data is based on a fixed interval nonlinear stochastic smoothing scheme and produces an estimate that evolves continuously in time. For each instant of time, the post mission position estimate is based on all the information collected during the mission, as opposed to real time estimates that can only take into account past data.