DEEPWATER MOORING

DEEPWATER MOORING

DEPLOYMENT EXAMPLE

PAYLOAD:

  • Seabird SBE37-IM CTD

  • Also included telemetry of instrumentation below the WW mooring.

INSTITUTION:

NASA’s Jet Propulsion Laboratory and Scripps Institution of Oceanography

DEPLOYMENT LOCATION:

300 km west of Monterey, California and Cortes Bank off San Diego, California

SCIENTIFIC SUMMARY:

NASA’s Jet Propulsion Laboratory (JPL) will be launching a new Surface Water and Ocean Topography (SWOT) satellite, planned for November 2022. Onboard the satellite, a next-generation altimeter using a wide-swath Ka-band interferometer (KaRIn) will collect detailed global measurements of Earth's surface water and sea surface height.

Calibration and validation (Cal/Val) are important for any satellite mission. For the SWOT mission, a portion of the Cal/Val activities include the assessment of the measurement performance relative to direct ocean measurements of sea surface height (SSH). In the open ocean, SSH is connected to the distribution of temperature, salinity, and density. These properties must be measured with high vertical and temporal resolution to provide a ground truth for the satellite. With a planned launch in late 2022, a key portion of the NASA SWOT mission oceanography Cal/Val plan will use an array of moorings, four of which will be Wirewalker profilers, situated directly under the satellite flight path to gather snapshots of steric height to compare to the measurements gathered from space. These moorings are designed to withstand all weather and provide high data density in the upper part of the ocean, where the density field changes rapidly.

The Wirewalker provides a cost-effective way to gather high resolution data in the top 500 m, with a single instrument driven up and down a wire using wave energy. The Wirewalker has already proven effective across these depths, and the key innovation for this project is upscaling to full open ocean depth modality. The design combines a conventional taut mooring from the sea floor to 600 m depth with the Wirewalker operational in the top 500m, producing vertical profiles of density every hour. Using inductive technology, all of the data from the seafloor through the entire water column are transmitted in real-time. While the Wirewalker can carry a wide range of instruments, for this project they will be equipped with CTDs.

A pre-launch field campaign was conducted during winter 2019-2020 to assess the ground truth instrumentation prior to launch of the satellite. This site was 300 km west of Monterey, California, in the heart of the North Pacific storm track, and at a depth of approximately 5 km. The moorings performed well in these fully exposed conditions, giving confidence in their future deployment for SWOT satellite validation that will be in the rough seas off Point Conception in the depth of winter. During this pre-launch field campaign phase, the Wirewalker yielded about 3500 roundtrip profiles to 500m (~3500 km travelled), during its 86 days of deployment. The mooring allowed a full-ocean depth estimate of SSH with an uncertainty of less than 1 cm, according to results published this year in the Journal of Atmospheric and Oceanic Research by a team of institutions led by JPL (https://doi.org/10.1175/JTECH-D-21-0039.1). Additionally, a similar mooring was recovered in spring 2022 after 223 days near Cortes Bank off San Diego, California; yielding about 7400 roundtrip profiles to 500 m (~7400 km traveled), with an average repeat rate of one cycle every 43.4 minutes.

 

REFERENCES:

Deployment ExamplesChris KontoesCTD