Passive acoustics embedded on gliders—Weather observation through ambient noise

Abstract

Underwater gliders can provide high resolution water temperature and salinity profiles. Being able to associate them with a surface weather conditions estimation would allow to better study sea-air interactions. Since in-situ observations of the marine meteorological parameters are difficult, the development of a glider embedded weather sensor has been studied, based on the WOTAN approach. In the 1–30 kHz frequency range, the background underwater noise is dominated by wind generated noise. Focusing on the sound pressure level at 5, 8, 10, and 20 kHz allows to estimate the wind speed. Thus, deploying a glider with an embedded hydrophone gives an access to the surface weather conditions around its position. We have deployed gliders in the Mediterranean sea, with passive acoustic monitoring devices onboard. Four months of data have been recorded. Wind speed estimations have been confronted to weather buoys observations and atmospheric models predictions. Wind estimates have been obtained with a ~2 m/s error. A specific emphasis has been placed on the robustness of the processing through multi frequencies analysis and depth induced attenuation correction. A downscaling study has been performed on the acoustic sampling protocol, in order to meet the low energy consumption glider standards, for a future real time embedded processing. The glider generated noise and its vertical movement are not perturbing the estimation. Moreover, the surface behavior of the Slocum gliders allows an estimation of the wind direction.

Wind Speed Estimation Using Acoustic Underwater Glider in a Near-Shore Marine Environment

“…This highlights the importance of selecting a buoy as close as possible to the acoustic recorder. In the literature, average distances between recorders and buoys (or onshore meteorological stations) vary from 40 km [19] to 80 km [20]. In our study, maximum time and space intervals between the glider and buoy 44013 were 1 h and 24 km.…”

“…This wind speed will be called the acoustic wind speed W ac . In the literature, various regression models have been used to link W gt and W ac , such as linear [19], logarithmic [2], [3], quadratic [20], or third-order polynomial [4]. Following the method proposed by Ma et al [2, Appendix A], some papers use feature normalization to make their conversion model independent of recording sites and acquisition parameters.…”

“…Then, to reduce the dimension of our SPL vector, we only keep the SPL( f c ) measures per octave that maximize the Pearson correlation coefficient with the variable W 44013 . The acoustic descriptors resulting from this process, also listed in Table I, form a 10-D feature vector over all the observations consisting of the following descriptors: SPL(0.1), SPL(0.7), SPL(1.8), SPL(5), SPL(8), SPL(11), SPL( 14), SPL (19), SS(2-8), and SS (8)(9)(10)(11)(12)(13)(14)(15). In the following, all f c values are rounded to a multiple of 100 Hz for clarity in the notation, and all SPLs are given in dB ref μPa 2 .…”

“…To the best of authors' knowledge, no peer-reviewed publication exists that report results on using acoustic glider technology for meteorological applications. Nonetheless, Cauchy et al [19] have validated the feasibility of estimating wind speed from glider data with an average absolute error of 2 m • s −1 , and observed that depth-related errors marginally impacts this estimation. Furthermore, the study in [19] has used a clean acoustic scene in deep water, far from the coasts, and largely predominated by wind speed.…”

Tertiary Waves Measured during 2017 Pohang Earthquake Using an Underwater Glider

“…Among these platforms, underwater gliders have been actively used for measurement of environmental underwater ambient noise. The addition of a single hydrophone sensor to an underwater glider provides a capability for measurement of underwater noise level [7][8][9][10][11][12][13][14] and the addition of a hydrophone array enables surveillance of the underwater acoustic environment [15,16].…”