The Gulf of Mexico is home to the highly energetic ocean circulation feature known as the Gulf Loop Current System (LCS). This current system influences all ocean processes in the Gulf, characterised by highly disruptive Loop Current Eddy (LCE) events. LCEs are rings of warm water which rotate at speeds of up to four knots in a clockwise direction, measuring approximately 100-200 km in diameter, reaching down to depths of 500–1000 m, and breaking away from the extended Loop Current around every 8-9 months. Loop Current Eddy events have serious implications for a great range of natural and human activities, from ecosystem dynamics and hurricane intensification to fishing operations and oil and gas exploration.
The challenge
The behaviour of the LCS remains difficult to forecast with sufficient accuracy to guide operations beyond a few days, yet its significance for processes and operations in the Gulf of Mexico drives a need to improve and extend forecasts of the LCS and LCEs. The difficulty has arisen partly because interactions of the upper currents with deep eddies have not been detectable in real time to guide numerical models.
Unlocking the Gulf current – a continuance
Sonardyne were introduced to this challenge back in 2018 when the University of Rhode Island launched a multi-year scientific study that included deployment of five Sonardyne Current Pressure Inverted Echo Sounders (CPIES) at depths down to 3500 m in the area of the extended LCS.
The Sonardyne solution
Sonardyne’s modem-enabled CPIES were a key element in the initial two-year project. These instruments were part of a mass deployment to measure two-way travel time (or tau) over an extended area in order to map the local horizontal velocity and density fields in the extended LCS, as can be read at https://www.sonardyne.com/case-study/unlocking-the-gulf-loop-current/.
Soon after the 2018 deployment, Sonardyne began the development of Origin 65, a combined PIES and ADCP with acoustic modem to enable adaptive data harvesting. The benefit of Origin 65 over CPIES is that it not only supports but augments density/current mapping projects.
Where CPIES use a separate single point current meter to provide a deep reference velocity for calculated geostrophic currents, Origin 65 measures a whole profile of currents over a greater range. Being an all-in-one instrument, Origin 65 also removes the risk and expense of combining separate devices for a single application.
What’s more, by utilising Origin 65’s onboard Edge data processing capability, PIES data is time-synchronised and fused with the ADCP measurements for simpler analysis. After extensive trials, Origin 65 was launched in 2023.
“Pulses of strong currents pose a hazard to industry along steep escarpments in the deep Gulf. Moreover, their unexpected arrival compounds the hazard: satellite and near-surface observations and numerical models do not predict them reliably. We needed a forecast tool grounded in observations with adaptive reporting capability. We had a tall order for the observations: We needed to profile currents from the bottom through hundreds of meters above the bottom and we required fast acoustic telemetry capability. Sonardyne committed the engineering capability to develop a combined PIES and upward-looking low frequency ADCP with a vertical range of 800m. It was an outstanding match to our needs, and Sonardyne’s fast acoustic telemetry capability was key to being able to harvest the data and report it ashore in near-real time.”
Professor D. Randolph (Randy) Watts, Professor of Oceanography, University of Rhode Island
The 2024 deployment
In 2024, funded by the US National Academies of Science, Engineering, and Medicine Gulf Research Programme and led by a team of scientists from the University of Rhode Island, five Sonardyne Origin 65 units were deployed alongside the original Sonardyne CPIES in the Gulf of Mexico (depth range of 1800 – 3200 m) for an initial 18-month measurement campaign.
Both the Origin 65s and CPIES have integrated acoustic modems enabling high-speed (up to 9000 bps) acoustic telemetry to support wireless retrieval of data by an uncrewed surface vessel (USV) in addition to remote control of the instruments.
Despite similar telemetry capability, the volume of data generated by Origin 65 compared to CPIES is much greater, and therefore limited acoustic bandwidth presents a challenge when looking to transfer this substantial data via acoustic telemetry.
This is where Origin 65’s Edge onboard data processing capability comes into play to condense the bulky raw data into small packets of actionable information, easily exportable via the acoustic modem.
The five Origin 65 units were deployed with an Edge application (app) installed to perform combined onboard processing of the ADCP and PIES data. More specifically, the Edge app implemented a custom algorithm that produced an hourly compact (24 bytes) binary output containing a timestamp, the mean current speed and bearing in six depth-bins above the bottom, plus the mean of the PIES results.
The beauty of the onboard data processing was apparent during planned USV visits, where it took less than 20 minutes to acoustically harvest more than 2 months’ worth of data
An assessment was conducted whereby the integrated acoustic release on one of the Origin 65 instruments was triggered after 66 days of deployment to allow recovery (Figure 1) of the device and complete data download for a thorough evaluation. This instrument was located in a water depth of 2142 m.
Figure 1: Retrieval of the Origin 65 aboard the R/V Pelican.
Pies
The PIES portion of the Origin 65 performed consistently (Figure 2). Periods of increased scatter in the sound speed measurements are observable, but these are a result of higher ambient noise levels (pretrigger RMS), which correspond to higher sea states (local wave activity is a dominant source of acoustic noise given that in higher sea states the surface return from the PIES chirp is more spread out).
Figure 2: PIES sound speed and ambient noise (pretrigger RMS) measurements for the deployment. The bottom plot compares ambient noise (pretrigger RMS) to the level of local wave activity using wind speed (as recorded by station Green Canyon 338, 124 km to the WNW of the deployment site) as a proxy for sea state.
ADCP
Velocity data demonstrates expected current behaviour (Figure 3), with velocities much larger in the Eastward and Northward directions than in the upward direction. The lack of significant apparent velocity in the vertical direction indicates that there is no systematic bias in the beam-frame Doppler velocities.
In addition, the observed velocity signals (large blue and red patches) vary on timescales between days and weeks, which is expected.
Of particular interest, it can be seen around 6th June, the prevailing current changed from South-Easterly to North-Westerly over the course of around two days.
This corresponded with a sudden increase in scatter density, thought to be an indication that the seabed was disturbed by the changing current.
Figure 3: Components of the Earth-frame velocities for the 66-day deployment (60-ping ensembles).
Low scatterer concentration in the deep waters (>2000 m) of the Gulf of Mexico reduced the effective profiling range of the Origin 65 from its achieved maximum range of > 800 m. However, with a sufficiently long averaging period it can been seen that the current velocity signal is present for the entire 800 m range of the Origin 65 (Figure 4).
Figure 4: Comparison of 24-hour averages of Eastward current velocity for different altitude bins. Performing increased averaging shows that a consistent current velocity signal is exhibited across the 800 m range of Origin 65.
“Our collaboration with the University of Rhode Island has been instrumental in augmenting our PIES technology in the form of Origin 65, a combined ADCP and PIES, for oceanographic study of geostrophic currents fields like that found in the Gulf of Mexico. We’re delighted to see Origin 65 being applied in this vital study, and by extension, to be able to support research efforts to improve and extend forecasting of the LCS and LCE behaviour with the accuracy desired. We look forward to continuing our relationship with the University of Rhode Island, and to seeing further successful USV data harvests from the Origin 65 units over their deployment period in the Gulf of Mexico.”
Michelle Barnett, Business Development Manager – Ocean Science, Sonardyne
What’s more, evidence of diel plankton migration is apparent with the repeated appearance and disappearance of a scattering layer between 500 m and 800 m height above the bottom. This pattern has a period of roughly 24 hours with the scattering layer clearly visible in daylight hours, as is consistent with the cycle of diel vertical migration observed ubiquitously in aquatic systems throughout the world.
This is nicely demonstrated in cross-correlation data, where values increased to around 80% on a daily cycle in response to the plankton migration (Figure 5). This cross-correlation data helps to indicate the effective maximum range of the system of around 800 m.
Figure 5: An excerpt (4 – 7th June) of unaveraged cross-correlation data for each of the four beams of the Origin 65 demonstrating a clearly observable diel vertical migration pattern. The lower plot represents the local time, with the colour being a function of the local solar altitude.
“This suite of instrumentation and platforms will help refine predictive tools for future applications in the Gulf. Looking ahead, the combination of Sonardyne Origin 65 current profilers and adaptive data-harvesting technology opens the door for long-term deployments in deep water – anywhere in the world. This is very exciting: we could access remote and critically important regions supporting sustained observations and advancing science.”
Professor Kathleen (Kathy) Donohue, Professor of Oceanography, University of Rhode Island
What’s next?
Two successful data harvests by a SeaTrac SP-48 USV equipped with a Sonardyne HPT 7000 L transceiver head have already been conducted. A third data harvest is scheduled for the end of July and the instruments will be recovered in September 2025. Keep an eye on our website and social media for further information about this and the data captured.
If you have an operational challenge for Origin 65, or any other Sonardyne product, please contact us.