Browsing by Author "Soares, C."
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- 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 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 Oceanographic Buoy testing during the Maritime Rapid Environmental Assessment 2003 sea trialPublication . Soares, C.; Jesus, S. M.; Silva, A.; Coelho, E.This paper proposes an innovative concept that responds to the requirements of acoustic REA as the integration between a network of sophisticated Acoustic-Oceanographic Buoys (AOB) and online ocean properties inversion algorithms. A prototype of the system, in- cluding one sonobuoy and a preliminary version of the inversion code, was tested at sea during the MREA'03 sea trial. The AOB is a light acoustic receiving device that in- corporates last generation technology for acquiring, storing and processing acoustic and non-acoustic signals received in various channels along a vertical line array. During the MREA'03 the AOB was deployed on a free drifting con guration. Source/receiver geom- etry was estimated from the buoy's GPS. Online processing was made possible by wireless transfer of the data and inversion was done in a range-dependent environment. Temper- ature pro les inverted from acoustic signals in two frequency bands on near
- 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.
- AOB - Acoustic Oceanographic Buoy: concept and feasibilityPublication . Jesus, S. M.; Soares, C.; Silva, A.; Hermand, J.-P.; Coelho, E.The AOB - Acoustic Oceanographic Buoy is the single node of a network of “smart” buoys for acoustic surveillance, Rapid Environmental Assessment (REA) and underwater communications. The AOB is a lightweight surface buoy with a vertical array of acoustic receivers and temperature sensors to be air dropped or hand deployed from a small boat. The received data is geotime and GPS precisely marked, locally stored and processed by on board dedicated DSP hardware. AOBs can exchange data over a local area network that includes submerged, sea surface (like for instance other AOBs) and air or land located nodes, allowing for the integration of all users in a seamless network. Specific software allows AOB usage in complex tasks such as passive or multistatic acoustic surveillance, acoustic observations for REA oceanographic forecast and model calibration, bottom and water column acoustic inversion, underwater communications and cooperating target tracking. The AOB was successfully deployed in several consecutive days during two Maritime REA sea trials in 2003 (Mediterranean), in 2004 (Atlantic) and for an high-frequency underwater communications experiment during MakaiEX, 2005 (Hawai). Data collected at sea shows that the AOB is a versatile, robust and easy to use tool for a variety of broadband underwater acoustic applications.
- AOB - an easily deployable, reconfigurable and multifunctional acoustic-oceanographic systemPublication . Jesus, S. M.; Soares, C.; Silva, A.; Hermand, J.-P.; Coelho, E.The concept of an easy to use and easy to deploy ocean acoustic tomographic OAT system is presented. The system is composed of a network of buoys and a data inversion online processor. This study concerns the individual node of that network—the acoustic-oceanographic buoy AOB —the data inversion technique and the testing of the system at sea. The AOB is a lightweight surface buoy with a vertical array of acoustic and temperature sensors to be hand deployed in a free-drifting configuration from a small boat. The data are locally stored and transmitted online to a remote station for processing and monitoring. Data inversion is based on a broadband matched-field tomography technique where known and unknown parameters are simultaneously searched for focalization . In situ recorded temperature data serve for algorithm initialization and calibration. The AOB was successfully deployed in several consecutive days during two rapid environmental assessment sea trials in 2003 Mediterranean and 2004 Atlantic . Data collected at sea also show that the AOB can be reconfigured as a receiving array for underwater coherent communications in the band up to 15 kHz.
- Asymmetric PCR ELISA: increased sensitivity and reduced costs for the detection of plant virusesPublication . Nolasco, Gustavo; Sequeira, Z.; Soares, C.; Mansinho, A.; Bailey, A. M.; Niblett, C. l.PCR ELISA is the immunodetection of the products of a polymerase chain reaction (PCR). It is effective for detecting and differentiating plant viral nucleic acids, but as currently performed, it is laborious and expensive. The procedure has been modified and simplified by using asymmetric PCR. This eliminated the need to denature and neutralize samples prior to hybridization. It also increased the relative concentration of the target DNA species, making PCR ELISA more sensitive than TaqMan(TM), a fluorescence-based detection method. Reducing the reaction volumes to half and the concentration of the dNTPs and the digoxigenin label by tenfold significantly reduced the costs of PCR ELISA without reducing its sensitivity. The usefulness of these modifications was demonstrated for the detection of Citrus tristeza virus and Rupestris stem pitting-associated virus. We expect that with only minor modifications asymmetric PCR ELISA could be used effectively for the detection of most nucleic acid molecules of interest.
- Blind ocean acoustic tomography: experimental results on the INTIFANTE'00 data setPublication . Jesus, S. M.; Soares, C.; Onofre, J.; Picco, O.Blind Ocean Acoustic Tomography (BOAT) is an ocean remote exploration concept similar to acoustic tomography but where both the emitted signal waveform and the source osition are unknown. BOAT consists of a minimal environmental model of the area, a broadband matched- eld processor and a genetic algorithm search procedure. This paper presents the results obtained with BOAT on part of the data set acquired during the INTIFANTE'00 sea trial, where an acoustic source was towed along both range independent and range dependent paths, with source-receiver ranges varying from 500 m up to 5.5 km and water depths varying from 70 to 120 m. The results obtained on several hours of data, show that source range and depth can be used as focalizing parameters, together with the Bartlett power to indicate model tness. Using this three parameters it becomes clear when the environment is \in focus" and when it is \out of focus" leading to realiable estimates of the geometric and environmental parameters under estimation.
- Broadband matched-field processing: coherent and incoherent approachesPublication . Soares, C.; Jesus, S. M.Matched-field based methods always involve the comparison of the output of a physical model and the actual data. The method of comparison and the nature of the data varies according to the problem at hand, but the result becomes always largely conditioned by the accurateness of the physical model and the amount of data available. The usage of broadband methods has become a widely used approach to increase the amount of data and to stabilize the estimation process. Due to the difficulties to accurately predict the phase of the acoustic field the problem whether the information should be coherently or incoherently combined across frequency has been an open debate in the last years. This paper provides a data consistent model for the observed signal, formed by a deterministic channel structure multiplied by a perturbation random factor plus noise. The cross-frequency channel structure and the decorrelation of the perturbation random factor are shown to be the main causes of processor performance degradation. Different Bartlett processors, such as the incoherent processor [Baggeroer et al., J. Acoust. Soc. Am. 80, 571-587 (1988)], the coherent normalized processor [Z.-H. Michalopoulou, IEEE J. Ocean Eng. 21, 384-392 (1996)] and the matched-phase processor [Orris et al., J. Acoust. Soc. Am. 107, 2563-2375 (2000)], are reviewed and compared to the proposed cross-frequency incoherent processor. It is analytically shown that the proposed processor has the same performance as the matched-phase processor at the maximum of the ambiguity surface, without the need for estimating the phase terms and thus having an extremely low computational cost. (C) 2003 Acoustical Society of America.
- Broadband MFP: coherent vs. incoherentPublication . Jesus, S. M.; Soares, C.Matched-Field Processing (MFP) is now a mature technique for source localization and tracking. There are at least two aspects that emerge, by their relevance, to the success of MFP: one is the ability of a given MFP processor to accurately pinpoint the source location while rejecting sidelobes, and the other is the impact of erroneous or missing environmental information (known as model mismatch) in the final source location estimate. This study addresses the first aspect regarding sidelobe rejection while considering that the processor is working on a mismatch free situation. One well known procedure to reduce sidelobes is to use a broadband MFP processor (whenever a band of frequencies is available). There are a number of different ways to combine MFP information across frequency that ran be classified in two broad groups: the conventional incoherent methods, that are based on the direct averaging of the auto-frequency inner products and the, say, less conventional methods, that perform a weighted average of the cross-frequency inner products where the weights are the frequency compensation phase-shifts. The later are generally termed as coherent broadband methods since they combine complex inner products. The coherent broadband methods proposed in the literature are either suboptimal or very computationally Intensive, even for a small number of frequencies. An alternative method is presented that combines cross-frequency information with the same localization performance than the standard coherent methods and a computation load similar to that of the incoherent processor. The performance of the various broadband processors is compared in simulated data.