Underwater noise as an indicator of geophysical processes occurring in an Arctic fjord

Oceany są miejscem o szczególnym znaczeniu dla kształtowania się klimatu Ziemi. Procesy wymiany energii pomiędzy morzem i atmosferą są źródłem dźwięków propagowanych pod powierzchnią wody w bardzo szerokim zakresie częstotliwości, gdzie łamiące się fale wiatrowe i opady atmosferyczne są dominującymi czynnikami kształtującymi pole szumów. W wodacharktycznych głównym źródłem dźwięków podwodnych jest pokrywa lodowa. Są to przede wszystkim dźwięki generowane przez przemiany lodu morskiego oraz dźwięki towarzyszące topniejącym górom lodowym pochodzącym z cielących się lodowców. Przedstawione wyniki badań hydroakustycznych prowadzonych w fiordzie Hornsund i wyniki badań laboratoryjnych umożliwiły precyzyjne określenie źródeł hałasów podwodnych generowanych podczas procesutopnienia lodu. Rejestracje uwalnianych z lodu pęcherzyków gazowych za pomocą kamery o prędkości 6000 klatek · sek–1 i równoległej rejestracji akustycznej umożliwiły prześledzenie procesu generacji dźwięku i zbudowanie modelu fizycznego obserwowanego zjawiska. Wyniki prowadzonych w fiordzie Hornsund badań hydroakustycznych mają znaczenie znacznie większe od lokalnego, ponieważ lodowce tego fiordu są typowymi dla atlantyckiego sektora Arktyki

Spatial distribution of macroalgae along the shores of Kongsfjorden (West Spitsbergen) using acoustic imaging

AbstractThe identification of macroalgal beds is a crucial component for the description of fjord ecosystems. Direct, biological sampling is still the most popular investigation technique but acoustic methods are becoming increasingly recognized as a very efficient tool for the assessment of benthic communities. In 2007 we carried out the first acoustic survey of the littoral areas in Kongsfjorden. A 2.68 km2area comprised within a 12.40 km2euphotic zone was mapped along the fjord’s coast using single- and multi-beam echosounders. The singlebeam echosounder (SBES) proved to be a very efficient and reliable tool for macroalgae detection in Arctic conditions. The multibeam echosounder (MBES) was very useful in extending the SBES survey range, even though it’s ability in discriminating benthic communities was limited. The final result of our investigation is a map of the macroalgae distribution around the fjord, showing 39% macroalgae coverage (1.09 km2) of investigated area between isobaths -0.70 m and -30 m. Zonation analysis showed that most of the studied macroalgae areas occur up to 15 m depth (93%). These results were confirmed by biological sampling and observation in key areas. The potential of acoustic imaging of macrophytes, and a proposed methodology for the processing of acoustic data, are presented in this paper along with preliminary studies on the acoustic reflectivity of macroalgae, also highlighting differences among species. These results can be applied to future monitoring of the evolution of kelp beds in different areas of the Arctic, and in the rest of the world.</jats:p

Two-element acoustic array gives insight into ice-ocean interactions in Hornsund Fjord, Spitsbergen

AbstractGlacierized fjords are dynamic regions, with variable oceanographic conditions and complex ice-ocean interactions, which are still poorly understood. Recent studies have shown that passive underwater acoustics offers new promising tools in this branch of polar research. Here, we present results from two field campaigns, conducted in summer 2013 and spring 2014. Several recordings with a bespoke two-hydrophone acoustic buoy were made in different parts of Hornsund Fjord, Spitsbergen in the vicinity of tidewater glaciers to study the directionality of underwater ambient noise. Representative segments of the data are used to illustrate the analyses, and determine the directions of sound sources by using the time differences of arrivals between two horizontally aligned, broadband hydrophones. The results reveal that low frequency noise (&lt; 3 kHz) is radiated mostly from the ice cliffs, while high-frequency (&gt; 3 kHz) noise directionality strongly depends on the distribution of floating glacial ice throughout the fjord. Changing rates of iceberg production as seen for example in field photographs and logs are, in turn, most likely linked to signal amplitudes for relevant directions. These findings demonstrate the potential offered by passive acoustics to study the dynamics of individual tidewater glaciers.</jats:p

Measurement of Seafloor Acoustic Backscatter Angular Dependence at 150 kHz Using a Multibeam Echosounder

Acoustic seafloor measurements with multibeam echosounders (MBESs) are currently often used for submarine habitat mapping, but the MBESs are usually not acoustically calibrated for backscattering strength (BBS) and cannot be used to infer absolute seafloor angular dependence. We present a study outlining the calibration and showing absolute backscattering strength values measured at a frequency of 150 kHz at around 10–20 m water depth. After recording bathymetry, the co-registered backscattering strength was corrected for true incidence and footprint reverberation area on a rough and tilted seafloor. Finally, absolute backscattering strength angular response curves (ARCs) for several seafloor types were constructed after applying sonar backscattering strength calibration and specific water column absorption for 150 kHz correction. Thus, we inferred specific 150 kHz angular backscattering responses that can discriminate among very fine sand, sandy gravel, and gravelly sand, as well as between bare boulders and boulders partially overgrown by red algae, which was validated by video ground-truthing. In addition, we provide backscatter mosaics using our algorithm (BBS-Coder) to correct the angle varying gain (AVG). The results of the work are compared and discussed with the published results of BBS measurements in the 100–400 kHz frequency range. The presented results are valuable in extending the very sparse angular response curves gathered so far and could contribute to a better understanding of the dependence of backscattering on the type of bottom habitat and improve their acoustic classificatio