Abstract
Despite huge advances in wireless communications in the last few years, underwater wireless communications is still a not fully developed technology, due to the lack of efficiency of radio waves for underwater communication. This problem can be overcome by using acoustic waves instead. In order to implement high-speed acoustic communications, it is imperative to develop transducers with high performance at high frequency. In this paper, a study of both piezoelectric ceramics and polymers used as water-coupled ultrasonic transducers is presented. As the main goal is to analyze their performance for high-speed communications, the behaviour of the piezoelectric ceramic (lead zirconate titanate, PZT) and the piezoelectric polymer (poly(vynilidene fluoride), PVDF) at high frequencies in underwater environment are compared. Results show that PVDF has a better response under the same ideal conditions, mainly with increasing frequency. (C) 2010 Published by Elsevier Ltd.

Abstract
This paper presents an embedded hardware/software implementation for the computing system of a small scale unmanned autonomous sailing boat. The system is integrated in a single XILINX FPGA, and hosts a Microblaze soft processor surrounded with heterogeneous, custom designed, control and processing modules than handle the interface with all the sensors, actuators and communication devices of the sailing boat. These interfacing modules implement tasks that have been decentralized from the main processor, thus alleviating its computational load and providing processing time for higher level software applications. Using an FPGA to implement an integrated single-chip computing system, as an alternative to conventional processors, has proven to be a very flexible solution as it eases the migration of computation tasks between the hardware and software domains, and more importantly, allowing the rapid adaptation of the digital interfacing hardware in order to support additional peripheral devices required for an application mission. The software component of the boat's control system runs on the top of the uClinux embedded operating system and is formed by various concurrent applications developed in C with the standard Linux libraries. The remote monitoring, configuration and operation of the sailing boat is done via a WiFi link, using a graphics interactive application that runs on a conventional PC.

Abstract

Abstract
This paper describes the interaction between the kinematic model of the AUV MARES, and the measurement and observation of the environment through images obtained with the sonar use. Three types of Sonar are discussed in this paper; there are forward-look, side scan and multibeam. But the sonar used to develop this work was the side scan sonar. The type of observations and characteristics of the environment provided by the sonar are described here. The method, which connects the sensory part of the vehicle with the observations of the sonar, was the Kalman filter (EKF). In this paper, are presented two simulations of filters for two different characteristics. Both filters estimate the characteristics of natural landmarks, creating an environment map, but both of them consider different states of the vehicle. Results of the simulation are obtained. The features that are considered are an underwater pipe on the floor and a wall. It also generated a control for the vehicle that provides the capacity to move along the feature/landmark from a reference distance.

Abstract
This paper describes an algorithm to make the treatment, segmentation, skeleton and characteristics extraction from acoustic images obtained from a side scan sonar. The fundamental goal is to implement a system that endows a autonomous vehicle with the capacity to know its own distance to the marine bottom and to features located on the marine environment. This features extraction would improve vehicle navigation and allow it to navigate relative to features like an underwater piper on the sea floor or a vertical wall. This paper was made based on Imagenex Sport Scan (side scan sonar) whose function is the observation of environment. Also the autonomous surface vehicle (ASV) ZARCO was used to transport the side scan sonar. Both the vehicles belong to The OceansSys Group DEEC-FEUP. A communication interface between the ASV ZARCO, Imagenex Sport Scan, and a static laptop that allows the observation of sonar data in real time is also described in this paper. The algorithms and routines implemented were validated with real acoustic images acquired during a mission. Results from algorithms application and features extraction are shown in this paper.

Abstract
This paper describes an interferometric synthetic aperture sonar system based on an unmanned surface vehicle customized for shallow water environments. Synthetic aperture sonar enables imagery of high resolution that is independent of range by using the displacement of the sonar platform to create a large virtual array. If two geometrically displaced images are obtained, the construction of three-dimensional topographic maps is possible through the use of interferometric techniques. The use of an unmanned surface vehicle presents several advantages that alleviate some problems related to the formation of synthetic aperture images, which are mainly related to the fact that a precise navigation system can be used for the boat control and sonar imagery motion compensation. Also, a small unmanned surface vehicle is advantageous in terms of cost of operation, maintenance and ease of deployment. Mapping of shallow water areas is an important task for many commercial and scientific applications like river navigability, infrastructure maintenance and natural resource monitoring. These tasks can be done efficiently with this system. Sample data obtained during test trials illustrate how synthetic aperture can be used to generate underwater imagery and bathymetric data.