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- 5th International European Turfgrass Society Conference: Crop Science Special IssuePublication . Guerrero, Carlos
- Acoustic emission and reception unit (AERU)Publication . Saleiro, MárioThis document describes a data acquisition/data generation system, which consists of a portable waterproof case with all the integrated electronics. It features a high power battery, a precision DAQ board, a state-of-the-art GPS board and a complete computer system. Acquired data can be stored in the internal hard drive and download into another storage device or directly to another computer using the Ethernet connection. It is intended to be used with the Portable Acoustic Source Unit (PASU) for acoustic data transmission and with single or multiple hydrophones for acoustic data acquisition. The system also features a easy and ready-to-use graphical user interface that allows the user to use the system using the integrated LCD touch screen. A user manual is included as an installation, setup and maintenance guide for the system and its practical applications. The developed hardware and software is described in detail. Detailed schematics and designs can be found in the final section of this document, which can be used to further develop the system, perform maintenance, purchase spare parts or perform any type of modifications. A support equipment named OCU (Outdoor Communications Unit) is also described in this document. The OCU consists of a waterproof case that can be used to supply the AERU or the PASU and to add wireless connectivity to the AERU it can also provide a handy solution to charge the batteries of the AOB2 buoys in a wet deck environment. ACKNOWLEDGMENT:
- Acoustic maritime rapid environmental assessment 2004 during the MREA'04 sea trialPublication . Jesus, S. M.; Soares, C.; Felisberto, P.; Silva, A.; Farinha, L.; Martins, C.Environmental inversion of acoustic signals for bottom and water column properties is being proposed in the literature as an interesting concept for complementing direct hydrographic and oceanographic measurements for Rapid Environmental Assessment (REA). The acoustic contribution to REA can be cast as the result of the inversion of ocean acoustic properties to be assimilated into ocean circulation models specifically tailored and calibrated to the scale of the area under observation. Traditional ocean tomography systems and methods for their requirements of long and well populated receiving arrays and precise knowledge of the source/receiver geometries are not well adapted to operational Acoustic REA (AREA). The Acoustic Oceanographic Buoy (AOB) was proposed as an innovative concept that responds to the operational requirements of AREA. That concept includes the development of water column and geo-acoustic inversion methods being able to retrieve environmental true properties from signals received on a drifting network of acoustic-oceanographic sensors - the AOBs. An AOB prototype and a preliminary version of the inversion code, was tested at sea during the Maritime Rapid Environmental Assessment 2003 (MREA’03) sea trial and was reported in [1]. On a separate register it should be noted that the characterization of the environment between the source and the receiver also contributes to the identification of the acoustic channel response and therefore provides a basis for fulfilling the objectives of project NUACE1. The present report describes the data sets and results gathered during the MREA’04 sea trial that took place from 29 March to 19 April 2004 off the west coast of Portugal, south of Lisboa (Portugal), with the objectives of testing an improved version of the individual AOB and its functionality in a simple network. The acoustic part of the experiment lasted for four days between April 7 and April 10, 2004 and involved the transmission and reception of pre-coded signals along range-dependent and range-independent acoustic tracks.
- Acoustic monitoring of the oxygen production of a seagrass meadowPublication . Felisberto, P.; Zabel, F.; Martins, C.; Jesus, S. M.This paper discusses the data acquired in the Bay of la Revellata, Calvi, Corsica during October 2011 for the purpose of developing an acoustic system for monitoring the oxygen production of a seagrass meadow. In a range dependent very shallow water area, densely covered by Posidonia Oceanica seagrass , a sound source transmitted chirp signals in 3 different bands (400-800Hz, 1.5-3.5kHz and 6.5-8.5kHz) to 100m distant 3 self-recording hydrophones during a period of one week. Preliminary data analysis shown a possible correlation between the oxygen production and the instantaneous impulse responses observed. Using a simple procedure to estimate the received power allows to obtain figures of variability along time that seem to be highly correlated with oxygen production and show similar trend with oxygen measurements by optodes conducted in the same area. Those preliminary results show that a light acoustic system can potentially be used in a monitoring system to quantify the oxygen production of a seagrass meadow. The calibration of the acoustic method with other oxygen measurements is an ongoing work.
- Acoustic oceanographic buoy (version 1)Publication . Silva, A.; Martins, C.; Jesus, S. M.One of the known impairements in the application of ocean acoustic tomography in operational scenarios has been the size, weight and difficulty of operation of actual ocean going equipment, such as hydrophone arrays and acoustic sources. The Acoustic Oceanographic Buoy - AOB is meant to be, at its final stage, an easy to deploy and easy to maintain autonomous vertical array that puts together in a single system acoustic and non-acoustic sensors, self-storing of geotime and GPS referred data, on the buoy preprocessing capabilities and network seamless integrability and data online transfer via a wireless lan high speed link. These capabilities make the AOB a versatile system for a variety of applications such as ocean tomography, underwater communications, rapid environmental assessment (REA), passive and multistatic sonar and underwater target tracking. The AOB version 1 described in this report was developed between 2003 and 2004 and tested at sea during the MREA’03 and MREA’04 sea trials.
- Acoustic oceanographic buoy (version 2)Publication . Zabel, F.; Martins, C.This report describes an underwater acoustic data acquisition system, which uses a surface buoy and an underwater array of acoustic and non-acoustic sensors. The surface buoy includes a digital storage unit for the acquired data, a communications system for remote monitoring and data transmission, a digital processing unit for pre-processing of acquired data and a battery power supply. A user manual is included as an installation, setup and maintenance guide for the system and its practical applications. The developed hardware and software is described in detail. Detailed schematics and designs can be found in the final section of this document, these can be used to develop the system, perform maintenance, purchase spare parts or perform any type of modifications.
- Acoustic oceanographic buoy data report Makai Ex 2005Publication . Jesus, S. M.; Silva, A.; Zabel, F.It is now well accepted in the underwater acoustic scientific community that below, say, 1 kHz acoustic propagation models are accurate enough to be able to predict the received acoustic field up to the point of allowing precise and reliable source tracking in range and depth with only limited environmental information. This results from a large number of studies both theoretical and with real data, carried out in the last 20 years. With the event of underwater communications and the necessity to increase the signal bandwidth for allowing higher communication rates, the frequency band of interest was raised to above 10 kHz. In this frequency band the detailed knowledge of the environment - acoustic signal interplay is reduced. The purpose of the MakaiEx sea trial is to acquire data in a complete range of frequencies from 500 Hz up to 50 kHz, for a variety of applications ranging from high-frequency tomography, coherent SISO and MIMO applications, vector - sensor, active and passive sonar, etc...The MakaiEx sea trial, that took place off Kauai I. from 15 September - 2 October, involved a large number of teams both from government and international laboratories, universities and private companies, from various countries. Each team focused on its specific set of objectives in relation with its equipment or scientific interest. The team from the University of Algarve (UALg) focused on the data acquired by their receiving Acoustic Oceanographic Buoy - version 2 (AOB2) during six deployments in the period 15 - 27 September. This report describes the AOB2 data set as well as all the related environmental and geometrical data relative to the AOB2 deployments. The material described herein represents a valuable data set for supporting the research objectives of projects NUACE1, namely to fulfill NUACE’s task 3 and 4 and RADAR2, namely its tasks 2 and 3 devoted to the developement and testing of a field of sonobuoys.
- Acoustic Oceanographic Buoy Test during the MREA’03 Sea TrialPublication . Jesus, S. M.; Silva, A.; Soares, C.Environmental inversion of acoustic signals for bottom and water column properties is being proposed in the literature as an interesting concept for complementing direct hydrographic and oceanographic measurements for Rapid Environmental Assessment (REA). The acoustic contribution to REA can be cast as the result of the inversion of ocean acoustic properties to be assimilated into ocean circulation models specifically tailored and calibrated to the scale of the area under observation. Traditional ocean tomography systems and methods for their requirements of long and well populated receiving arrays and precise knowledge of the source/receiver geometries are not well adapted to operational Acoustic REA (AREA). An innovative concept that responds to the operational requirements of AREA is being proposed under a Saclantcen JRP jointly submitted by the the Universit´e Libre de Bruxelles (ULB), SiPLAB/CINTAL at University of Algarve, the Instituto Hidrogr´afico (IH) and the Royal Netherlands Naval College (RNLNC) and approved by Saclantcen in 2003 under the 2004 SPOW. That concept includes the development of water column and geo-acoustic inversion methods being able to retrieve environmental true properties from signals received on a drifting network of Acoustic-Oceanographic Buoys (AOB). A prototype of an AOB and a preliminary version of the inversion code, was tested at sea during the Maritime Rapid Environment Assessment’2003 sea trial (MREA’03) and is described in this report together with the results obtained.
- Acoustic rapid environmental assessment: the AOB conceptPublication . Jesus, S. M.; Soares, C.; Martins, N.Rapidly assessing the environmental conditions of a given coastal area with the capability of being able to predict its evolution in the next 24 or 48 hours has been the goal of many initiatives since the end of the cold war and the shift of strategic regions to shallow areas. Most efforts were carried out by oceanographic teams feeding data of various nature (currents, SST, temperature, altimetry, wave height, etc...) into small scale circulation models (such as mini HOPS and NCOM). Testing has been going on for several years on the validation of such models in various scenarios. Among others, the goal of this testing is to decrease the error variance of various environmental parameter predictions at 1, 2 or 3 days with a minimal model initialization.
- Active acoustic time-reversal for underwater acoustic barriersPublication . Jesus, S. M.This work addresses the possibility of using successive transmissions of time delayed channel probe pulses between two closely spaced acoustic sensor arrays for forming an acoustic barrier for target detection in shallow water. One array is a transmit-receive array (TRA) while the other is a receive only vertical line array (VLA). The two arrays are connected via cable or wireless. Time reversed replicas of the acoustic channel response to the probe signals are retransmitted into the ocean propagation plane to form focus peaks at each VLA element. It is shown both theoretically and with simulated data that an optimum disturbance detector can be build from the data received at the VLA. This detector becomes sub optimal due to usual time reversal drawbacks such as ocean non stationarity and spatial sampling limitations. Real data tests are foreseen to take place during summer 2007 to answer questions such as allowable ranges and frequencies of operation.