The new wave of oceanographers: Daocheng Yu

Physical oceanographer focusing on marine gravity recovery from satellite altimetry.

Daocheng Yu got his PHD from the Department of Civil Engineering, National Yang Ming Chiao Tung University, Taiwan.  He is now Associate Professor at the School of Geomatics, Liaoning Technical University, China.

SWOT AdAC: What is your field of research and how did you choose it?

Daocheng Yu: My field of research field is Geodesy, and in particular marine gravity recovery from satellite altimetry.

How exciting it is to reveal seafloor secrets from space! Satellite altimeter observations are helpful for us to explore seafloor topography. The sea surface heights measured by satellite altimeters can be used to derive marine gravity anomalies, which are useful for mapping the seafloor topography and determining the tectonic structures of the seafloor. Most of the seafloor tectonic are detected by the satellite-derived marine gravity field. It makes sense for me to further improve the accuracy and spatial resolution of the marine gravity field to discover uncharted tectonic features.

SWOT AdAC: How is your filed of research related to SWOT?

DY: The accuracies of the current marine gravity fields are about 3-5 mgal. The nominal grid intervals of these fields are 1×1 min, but the actual signal resolution (half-wavelength) may exceed 6 km. The accuracy and resolution of marine gravity field depend on the accuracy and resolution of the sea surface heights (SSHs) measured by satellite altimeters. A nadir-looking radar altimeter measures only SSHs along the satellite ground tracks to obtain one-dimensional SSH observations. The cross-track spacing of exact repeat missions (ERMs) is hundreds of kilometers, while that of geodetic missions (GMs) can be a few kilometers. Thus, GM data are mainly used to derive marine gravity field; however, the accuracies of GMs are lower than those of ERMs. Moreover, there are systematic and random errors in the SSH observations from different tracks, leading to spatially non-uniform SSH observations. In contrast, SWOT measures wide-swath SSHs with a nominal 2-km spatial resolution with unprecedented accuracy. Therefore, SWOT’s swath SSH observations outperform radar altimeter data in both spatial resolution and accuracy, leading to much improved marine gravity fields

SWOT AdAC: What do you find exciting about SWOT and the SWOT-AdAC campaign you will be participating? How will you contribute to the campaign?

DY: My past research has indicated that SWOT sea surface height (SSH) observations have the potential on deriving a high-accuracy marine gravity field. The north and east components of the deflection of the vertical (DOV), which can be used to recover marine gravity anomalies, determined from the current nadir-looking altimeters have different qualities. The accuracy of the north DOV component is better than that of the east DOV component because most satellites are in near-polar orbits. In theory, SWOT wide-swath observations can obtain the north and east DOV components with the same accuracy, which will improve the quality of the marine gravity field.

In the South China Sea and western Pacific campaign, our team proposes to recover the marine gravity field from SWOT 1-day repeated measurements in the South China Sea, which can be assessed by the shipborne gravity data. It is exciting that the marine gravity field derived from SWOT is better than that derived from conventional radar altimeters.

In the South China Sea and western Pacific campaign, I will pre-process the SWOT SSH observations in the fast sampling phase, and then derive marine gravity anomalies in the South China Sea. Because SWOT first observes wide-swath SSHs, some problems may arise when deriving marine gravity anomalies from SWOT data using the methods for processing the one-dimensional data from conventional altimeters. I will overcome these problems to obtain the optimal gravity field. I will combine the altimeter data from all the current altimeters to recover a best marine gravity field in the South China Sea, which is used to compare to the SWOT-derived gravity field. Also, I will detect sub-mesoscale oceanic eddies from SWOT measurements.

SWOT AdAC: What are your plans after the SWOT-AdAC campaign

DY: I plan to recover a high-accuracy and high-resolution marine gravity field in the South China Sea from the SWOT data in the science phase. I will improve the current methods for deriving marine gravity from the nadir-looking altimeters and even develop a new gravity recovery method for SWOT data. I will summarize optimal data processing for SWOT data. I hope that the best gravity field will discover some uncharted tectonic features of the seafloor.  If I have enough resources, I will determine a global marine gravity grid from 21-day repeated SWOT SSH measurements.