An Investigation of the Influences of SWOT Sampling and Errors on Ocean Eddy Observation

Abstract

The mission of Surface Water and Ocean Topography (SWOT) is scheduled to be launchedin 2022, and global ocean eddies with radius scales of larger than 10 km are expected to be observedfrom space. However, there are still open questions about the capability of SWOT to detect oceaneddies. Based on ocean model data and SWOT orbit, this study simulates along-track observationof SWOT. Two eddy datasets are derived from simulated observation data via mapping and eddyidentification procedures, one of which includes SWOT errors and the other does not. The thirdeddy dataset is generated from the original model data. Through comparing these three eddydatasets, it is found that 34% (40%) eddies are lost due to insufficient temporal sampling and errorsin the Kuroshio Extension (South China Sea) region, and numerous artifact eddies are generated.To further explain the influence of SWOT errors on smaller-scale eddies, two eddies (a cyclonic eddyand an anticyclonic eddy) with the radius of about 10 km are repeatedly observed 100 times usingthe SWOT-simulator. The cyclonic eddy with larger amplitude has been detected 84 times, whilethe anticyclonic eddy is visible 76 times. Therefore, the influence of the SWOT sampling and errorson ocean eddy observation is revealed by the results of these observing system simulationexperiments (OSSEs).

EddyGraph: The Tracking of Mesoscale Eddy Splitting and Merging Events in the Northwest Pacific Ocean

“…First, a global data set will be identified with improvements in computational efficiency. Second, in this study, we extracted typical events for validation due to the limited accuracy of our data set caused by the SLA data resolutions; the accuracy of our data set can be optimized with improvements in data resolution promoted by the progress of ocean remote sensing technology [38]. Third, our algorithm for tracking eddy splitting and merging events is based on the nature of eddies in two-dimensional SLA data.…”

A Simulation Experiment on In-Situ Observation of Short-Wavelength Scale Dynamic Processes and Potential Applications to Wide-Swath Interferometric Altimetry Validation

“…where p represents the pressure, ρ represents the density that can be decomposed as: 𝜌 = 𝜌 0 + 𝜌 ′ ( 6 ) where 𝜌 0 is the reference potential density (1027.5 kg/m3), 𝜌 ′ is the potential density anomaly. Equation ( 5) can also be expressed in the form: ( 7 ) In this equation, 𝑝 𝐴 refers to the atmospheric surface pressure, 𝑝 𝐵 refers to the bottom pressure of ocean, ζ is the SSH referenced to z = 0, and -h is the depth of the ocean. Transforming the above formula as…”

“…The Tiangong-2 [4] and soonto-be-launched "Surface Water Ocean Topography (SWOT) Mission" [5], "Guanlan" [6] and other possible missions will provide high-precision two-dimensional (2D) SSH data as the basis of the study of short-wavelength scale dynamic processes. Nevertheless, the simulation showed that more than one-third of eddies cannot be observed by SWOT in the high eddy kinetic energy (EKE) region (the Kuroshio Extension), even without considering the effect of internal tides [7]. Meanwhile, with the development of altimeter technology, the validation methods for conventional altimeters no longer meet the needs of many future altimeter missions, especially the validation requirements for WIA 2D data areas [8,9].…”

Analytical Models for Multipath and Switch Leakage for the SWOT Interferometer

“…The planned SWOT observatory [1][2][3][4], a collaboration between the US and French space agencies slated for launch in 2022, is designed to make high resolution, accurate two-dimensional measurements of ocean topography using SAR interferometry [5][6][7][8]. This unprecedented set of measurements would allow characterization of ocean mesoscale and sub-mesoscale dynamic processes [9][10][11] that are crucial to understanding and quantifying the exchange of energy between ocean layers and their impact on local and global carbon and energy budgets as well as nutrient transport [12,13]. The primary instrument on board the SWOT observatory enabling this unique set of measurements is KaRIn [14,15], a Ka-band (35 GHz) near-nadir radar interferometer capable of measuring sea-surface height with centimetric accuracy at kilometer scale resolutions [16], complemented with a nadir altimeter [17], GPS and DORIS [18] receivers and a three-frequency radiometer [19].…”