Since November 2015, two underwater gliders equipped with external hydrophones were deployed in the South Brazilian Bight in order characterize the area's soundscape. Contrasting to standard fixed mooring systems (where flow noise is generated by currents passing by the hydrophones), gliders are subject to noise generated by its own downward and upward motion, which may compromise soundscape characterizations if not properly evaluated. In order to investigate induced flow noise on the hydrophone and its characteristics, 563 hours of acoustic data from the gliders were correlated to the navigation settings. Results can be comparable to previous flow noise descriptions for fixed systems. A high correlation was observed between the glider speed (both vertical and total) and 1/3 octave band levels centered at frequencies below 20 Hz. Estimates of the broadband sound pressure level were accomplished with different lower frequency limits and found to be uncorrelated to the glider speed above 40 Hz.

Resumo: Até o presente momento não há uma regulamentação reconhecida pelos fabricantes de sensores de pressão submersíveis referente a especificações mínimas e procedimentos de calibração e teste. Uma metodologia para verificar a performance do sensor MS5803 foi elaborada com base em trabalhos realizados pela British Geological Survey. Uma plataforma, que futuramente poderá ser adaptada para medidas de campo, foi construida para permitir o levantamento das especificações do transdutor. Este trabalho foca no sensor MS5803-01 devido a sua popularidade em projetos de "hardware aberto" como por exemplo robôs submarinos, marégrafos/ondógrafos, computadores de mergulho, entre outros. Os resultados deste trabalho têm a itenção de ser uma fonte independente de dados de caracterização de forma a estender as informações providas pelo fabricante.Palavras chave: sensor de pressão, instrumentação submarina, transdutor de pressão submarino, sensor de profundidade, sensor piezoelétrico, calibração.Abstract: At this moment there is not any regulations adopted industry-wide for minimum specifications and calibration procedures to be used on submersible pressure transducers. A methodology was elaborated to verify performance characteristics of the MS5803 sensor following the guidelines of the British Geological Survey. A test platform, that can be easily adapted for field tests, was built to measure the transducer specifications. This work focus on the MS5803-01 sensor, since it's becoming popular in open projects ranging from underwater robotics (AUV and ROVs), wave/tide gauges and diving computers among many others. The results from this work intends to be an independent source of characterization data extending the information provided by the manufacturer.

No abstract

Nowadays, various collaborations are creating immense machines to try to track and understand the origin of high-energy cosmic particles (e.g., IceCube, ANTARES, Baikal-GVD, P-ONE). The detection mechanism of these sophisticated experiments relies mainly on an optical signal generated by the passage of charged particles on a dielectric medium (Čerenkov radiation). Unfortunately, the dim light produced by passing particles cannot travel too far until it fades away, creating the necessity to instrument large areas with short spacing between sensors. The range limitation of the optical technique has created a fertile ground for experimenting on the detection of acoustic signals generated by radiation—thermoacoustics. Despite the increased use of the thermoacoustic technique, the instrumentation to capture the faint acoustic signals is still scarce. Therefore, this work has the objective to contribute with information on the critical stages of an affordable submersible thermoacoustic sensor: namely the piezoelectric transducer and the amplifying electronics. We tested the sensor in a non-anechoic tank using an infrared ( ) Q-switched Nd:YAG laser as a pulsed energy source to create the characteristic signals of the thermoacoustic phenomena. In accordance with the thermoacoustic model, a polarity inversion of the pressure signal was observed when transiting from temperatures below the point of maximum density of water to temperatures above it. Also, the amplitude of the acoustic signal displayed a linear relationship with pulse energies up to ( ). Despite the use of cost-effective parts and simple construction methods, the proposed sensor design is a viable instrument for experimental thermoacoustic investigations on high-energy particles.