ship-based
(proposed)
infrastructure
(proposed)
ship-based
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infrastructure
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mooring

Insights on the design of the sampling strategy of the SWOT-AdAC Cal/Val campaign 

A SWOT Pre-launch field campaign conducted during 09/2019–01/2020 assessed the potential of various instruments and platforms to meet the SWOT Cal/Val requirement and shed light on the design of SWOT-AdAC California Cal/Val field campaign that will occur in 2023. 


Map of the SWOT Pre-launch field campaign instrumentation. Three moorings are marked by the three colored dots. The dashed yellow line is the glider target path of 60 km wide.

The Surface Water and Ocean Topography (SWOT) mission aims to map sea surface height (SSH) in wide swaths with an unprecedented spatial resolution and sub-centimeter accuracy. 

This improvement in resolution in respect to conventional satellite altimetry is expected to be groundbreaking for several key ocean questions, including the energy budget, the connection between surface and internal dynamics, biogeochemistry and biodiversity, and the dynamics at the ice margin.

But the instrument performance needs to be verified using independent measurements in a process known as calibration and validation (Cal/Val). The SWOT Cal/Val needs in-situ measurements that can make synoptic observations of SSH field over an O(100km) distance with an accuracy matching the SWOT requirements specified in terms of the along-track wavenumber spectrum of SSH error. No existing in-situ observing system has been demonstrated to meet this challenge. 

The study On the development of SWOT in-situ Calibration/Validation for short-wavelength ocean topography reports results of a field campaign conducted during 09/2019–01/2020 to assess the potential of various instruments and platforms to meet the SWOT Cal/Val requirements. These instruments include two GPS buoys, two Bottom Pressure Recorders (BPR), three moorings with fixed Conductivity-Temperature-Depth (CTD) and CTD profilers, and a glider. 

The observations demonstrated that: (1) the SSH (hydrostatic) equation can be closed with 1-3 cm RMS residual using BPR, CTD mooring and GPS SSH, and (2) using the upper ocean steric height derived from CTD moorings enable sub-centimeter accuracy in the California Current region during the 2019-2020 winter. Given that the three moorings are separated at 10-20-30 km distance, the observations provide valuable information about the small-scale SSH variability associated with the ocean circulation at frequencies ranging from hourly to monthly in the region. 

The combined analysis sheds light on the design of the SWOT-AdAC California Cal/Val field campaign that will occur in 2023. 

A minimum baseline for the SWOT postlaunch ocean Cal/Val field campaign.

FOR MORE INFORMATION

Wang, J., Fu, L., Haines, B., Lankhorst, M., Lucas, A. J., Farrar, J. T., Send, U., Meinig, C., Schofield, O., Ray, R., Archer, M., Aragon, D., Bigorre, S., Chao, Y., Kerfoot, J., Pinkel, R., Sandwell, D., & Stalin, S. (2022). On the development of SWOT in-situ Calibration/Validation for short-wavelength ocean topography, Journal of Atmospheric and Oceanic Technology