Yao Yu (UCSD, USA)

The marine geoid, which can be converted to sea surface slope and gravity anomaly, is
the principal signal in measurements of sea surface height. Gravity anomaly derived
from current radar altimeters, has an accuracy of 2-4 mGal and a spatial resolution
approaching 10 km (full wavelength). The swath measurements from SWOT may have
significantly lower noise and thus provide a major advance in the accuracy and
resolution of marine gravity. We use the Foundation seamounts area in the South
Pacific to assess the SWOT altimeter data collected during the first 90-days of the cal/val
orbit. These large seamounts have complete bathymetry and gravity coverage from two
shipboard surveys (Sonne – 1995 and L’ Atalante, 1997) and have some unique
characteristics that make an ideal location for calibration and validation of SWOT
measurements. 1) The 2-4 km tall seamounts formed on shallow seafloor near the
spreading ridge and thus have very large amplitude, short wavelength (~ 6 km) gravity
anomalies (~120 mGal). 2) The seafloor has a relatively uniform density because of thin
sediment cover. 3) The regions was sampled by the 1-day SWOT repeat orbit so many
repeats are available for stacking. 4) Ocean mesoscale variability is low in the region;
oceanographic “noise” is 50-100 times smaller than the gravity signal so can be largely
ignored in our analysis of SWOT data. We use the multibeam bathymetry to improve
the accuracy and resolution of the existing altimeter-derived gravity reaching an
accuracy of better than 2 mGal and a spatial resolution of 6.8 km as compared with the
shipboard gravity. We will use the gravity field in this region to assess the accuracy and
spatial resolution that can be achieved by SWOT from single and multiple passes.