Wind Speed Measured from Underwater Gliders Using Passive Acoustics

Abstract

Wind speed measurements are needed to understand ocean–atmosphere coupling processes and their effects on climate. Satellite observations provide sufficient spatial and temporal coverage but are lacking adequate calibration, while ship- and mooring-based observations are spatially limited and have technical shortcomings. However, wind-generated underwater noise can be used to measure wind speed, a method known as Weather Observations Through Ambient Noise (WOTAN). Here, we adapt the WOTAN technique for application to ocean gliders, enabling calibrated wind speed measurements to be combined with contemporaneous oceanographic profiles over extended spatial and temporal scales. We demonstrate the methodology in three glider surveys in the Mediterranean Sea during winter 2012/13. Wind speeds ranged from 2 to 21.5 m s−1, and the relationship to underwater ambient noise measured from the glider was quantified. A two-regime linear model is proposed, which validates a previous linear model for light winds (below 12 m s−1) and identifies a regime change in the noise generation mechanism at higher wind speeds. This proposed model improves on previous work by extending the validated model range to strong winds of up to 21.5 m s−1. The acquisition, data processing, and calibration steps are described. Future applications for glider-based wind speed observations and the development of a global wind speed estimation model are discussed.

Arctic Marine Data Collection Using Oceanic Gliders: Providing Ecological Context to Cetacean Vocalizations

“…In shallow water areas, and areas with high and variable current, such as on the continental shelf, the rate of self-noise is higher than off-shelf as the vehicle needs to use the buoyancy pump, altimeter and perform pitch/roll compensation more frequently. In addition, turbulent flow around the hydrophone results in flow noise proportional to the speed of the glider, particularly visible bellow 20 Hz, but likely present in the 5-50 Hz frequency band (dos Santos et al, 2016;Cauchy et al, 2018). This noise increases significantly above approximately 30 cm/s absolute velocity, indicating that for (a) reliable noise measurements at low frequencies (<50 Hz) and (b) high signal-to-noise ratio (SNR) for marine mammal detection at low frequencies, the glider should be operated with a low glide velocity when possible.…”

“…Ocean gliders are autonomous underwater vehicles (AUVs) developed for the purpose of marine surveillance. They provide high resolution (sensor dependent) hydrographic profiles and perform long duration missions, unaffected by extreme weather events (Rudnick, 2016;Cauchy et al, 2018). The potential for glider deployments with PAM systems allows for data collection through varying water masses and for long periods of time.…”

OceanGliders: A Component of the Integrated GOOS

“…Deployments of about a year are now possible, with deployments of 3-6 months now routine, and survey tracks extending over 1,000s kilometers. Sensors on gliders measure physical variables such as pressure, temperature, salinity, currents, turbulence and wind speed (Cauchy et al, 2018), biological variables relevant to phytoplankton and zooplankton, and ecologically important chemical variables such as dissolved oxygen, irradiance, carbon dioxide, pH (Saba et al, 2018), nitrate and hydrocarbon. Gliders have been developed to sample under-sea ice and ice shelves (Webster et al, 2015;Nelson et al, 2016;, to recover data from other deep instruments via acoustic telemetry and send them to land while at the surface (Send et al, 2013), to detect acoustic tags on fishes (Oliver et al, 2013(Oliver et al, , 2017 and marine mammals.…”

Ocean sound levels in the northeast Pacific recorded from an autonomous underwater glider

“…As wind speeds reach higher velocities greater than 9 m/s, the data become more scattered suggesting other significant sources were present during these high wind speeds (e.g. vessels) or a transition to another mechanism of wind generated noise at higher speeds may become more important [13, 33]. Estimates of the scaling factor for the spectral slope (n f ) of wind-dependent noise levels have typically been reported in the range of 0.5–1 for higher frequencies.…”

“…temperature, salinity, optical backscatter) has provided important new ecological insights for behavioral studies of low frequency baleen whales [6–8], high frequency beaked whales [9], tracking of sperm whales and other odontocetes [10], and acoustically active fish [11] throughout a range of mesopelagic and coastal habitats. An ocean glider equipped with a hydrophone logging system provided valuable information for a geophysical study describing the acoustic signals radiating from eruptive processes at a remote submarine volcano in the western Pacific Ocean [12], and acoustic recordings from an ocean glider in the Mediterranean Sea have recently been shown to accurately predict surface wind speeds [13]. Yet, despite the onset use of underwater gliders for acoustics around 2006, little or no research has addressed measurements of ambient noise level conditions.…”