Creative Research Science Experiences for High School Students

A French research institute raises the bar for public outreach with an educational laboratory that engages 1,000 high school students per year in mini research projects

UN SONDEUR MULTIFAISCEAUX DE NOUVELLE GÉNÉRATION : PRÉÉTUDES ACOUSTIQUES

On présente quelques résultats de préétudes et simulations préfigurant la conception d'un sondeur multifaisceaux de nouvelle génération, destiné à prendre la relève du SEA BEAM actuellement mis en oeuvre à partir du Navire Océanographique JEAN CHARCOT. L'évolution la plus marquante sera l'extension notable de la couverture : environ 8 fois la hauteur d'eau pour des fonds allant jusqu'à 2500m, 3 fois pour 5000m, 1 fois au delà de 7000m. Ceci induit des sites de sondage très obliques, inhabituels, et justifie une étude de la propagation. En parallèle, un certain nombre de simulations ont été effectuées pour optimiser la conception des antennes acoustiques afin de réduire les éventualités d'artefacts.Some results of simulation are presented concerning a new multibeam echosounder, which will equip the new R/V L'ATALANTE. This R/V will succeed to the R/V JEAN CHARCOT which was equiped with a SEA BEAM since 1977. The main point of interest is the increase in swath : near 8 times the water depth down to 2500m depth, 3 times down to 5000m, 1 time after 7000m. This involve very slant shots justifying propagation studies. In addition, simulation to optimize the antenna conception are presented

Un sonar latéral de nouvelle génération

Sidescan images of the sea-floor usually suffer from artefacts caused by the attitude variations of the towed platform. In collaboration with IFREMER, we are designing a system that compensates for yaw, pitch and roll in real time, i.e. during the whole ping cycle. The 4 m long antenna is made of 3 arrays working at 110 kHz. It enables ranges up to 1000 m and the angular resolution is 0.25° i.e. 1 m scan resolution for a 250 m range. The transmit array is made of 36 elements with 80 mm spacing. There are two identical receiving arrays, containing 32 active pieces each, with 120 mm spacing. The duplication of the receiving channel will give a bathymetric capability. Data provided by an attitude station are used to control the numerical beam-steering performed at transmit and during receive. On the other hand, 16 focal zones have been set to achieve a constant along-track resolution of 1 m up to 250 m range. In addition, focusing reduces the side-lobes level. The experimental results in water tank are in good agreement with the numerical model. First data and images were gathered during a campaign at sea in November 93

Un système d'imagerie 3-D

Within the EUROMAR 406 project, we have designed an acoustic camera that uses 2 orthogonal linear arrays. Site and azimuth scanning, at transmit and receive respectively, provides tridimensional data of the aquatic medium. The technology and morphology of the arrays are derived from a study on cylindrical antennas. Each array is 256 mm long and is made of 64 elements working at 500 kHz. These antennas are able to scan a 30°x30° sector with a 0.75° resolution. The grating lobes artefacts are rejected under -35dB. A fast dedicated numerical electronic system provides sectorial images in quasi-real time for ranges up to 100 m. The transmit fan beams scan the 30° wide sector according to 64 site directions and are wide open in the associated azimuth planes. Moreover they can be focused according to 32 finite distances. The 64 received signals undergo a continuous complex demodulation. A complex numerical computation (for 64 azimuths and 32 focal zones) over the 128 demodulated signals provides the sectorial image of the illuminated site at a rate of 2µs per pixel. The 3-D sector is acquired after N site shots (N<64) providing as many sectorial images. For example, with N=32, 1 s is needed to collect the domain between 9 m and 12 m range. In association with a microcomputer the system can provide front views. A frontal imaging mode may be obtained in real time by opening the transmit beam in both site and azimuth