Use of Underwater Gliders for Acoustic Data Retrieval from Subsurface Oceanographic Instrumentation and Bidirectional Communication in the Deep Ocean

Abstract

Many fixed oceanographic instruments and observing systems are deployed in the water column or on the seafloor for extended periods of time without any expression at the sea surface. To routinely communicate with such subsurface instruments in the deep ocean, here a system is presented that uses underwater gliders and commercially available acoustic modems for this task and its use is demonstrated with subsurface moorings and inverted echo sounders plus bottom pressure sensor (PIES). One recent glider mission spent 31 days in data retrieval dives, capturing 2 MB of error-free subsurface data. To acquire this volume, a total of 2.65 MB (including all retransmissions) were sent, with a success rate of 75%. A model for the energy usage of each phase of modem function was derived from laboratory measurements. While the model predicts that the glider would expend 0.21 J to acquire each data byte, the actual consumption of the glider in the field is 0.49 J byte 21 . The inefficiency is due to overhead associated with establishment of the acoustic link and with the resending of data that is received with errors. Including all the time for negotiating the acoustic link and for the retransmission of erroneous data, the net data throughput are around 3 bytes s 21 in spite of the modem operating at 140 to 600 baud. Even with these limitations, the technique has shown to be useful and is being utilized routinely in a research project in the California Current to obtain data from horizontal distances up to 7 km from an instrument at depths up to 4000 m, transferring on average 6 kB of data in a day of acoustic communications.

Global Perspectives on Observing Ocean Boundary Current Systems

“…Since 2005, autonomous underwater gliders have continuously surveyed along three of the CalCOFI lines as part of the CUGN (see the section Autonomous Underwater Gliders; Figures 1, 5) as well as along cross-shore transects as far north as the Washington Coast (Figure 5), returning measurements of physical properties and some biological proxies; the gliders complement the ship-based surveys by providing observations at higher spatial and temporal resolutions (e.g., Rudnick et al, 2017), albeit of a more limited set of properties. An array of PIES with end-point moorings off of Southern California monitors full-depth geostrophic transport; gliders routinely retrieve data from the PIES and transmit them to shore (Send et al, 2013). Since 2007, NOAA has led largescale coastal surveys along the U.S. West Coast every 2-4 years to determine the spatial distributions of carbon, oxygen, nutrient, biological, and hydrographic parameters (Feely et al, 2008(Feely et al, , 2018.…”

OceanGliders: A Component of the Integrated GOOS

“…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. Improved gliders have reached depths of up to 6,000 m (Osse and Eriksen, 2007).…”

Ocean Observations to Improve Our Understanding, Modeling, and Forecasting of Subseasonal-to-Seasonal Variability

“…Moorings, though challenging to maintain in strong current regions, can still act as an important source of measurements of surface fluxes that are useful for initializing S2S forecasts as well as verifying the forecasts (Cronin et al, 2008;Weller et al, 2012;Bigorre et al, 2013). Gliders are able to deliver the data from these moorings via real-time acoustic telemetry to monitoring and assimilation networks (Send et al, 2013). These should ideally be complemented by more spatially integrated transport and surface flux measurements in these regions for forecast validation.…”