Reconstructing Ocean Surface Current Combining Altimetry and Future
Spaceborne Doppler Data
Abstract
Two methods for the mapping of ocean surface currents from satellite
measurements of sea level and future current vectors are presented and
contrasted. Both methods rely on the linear and Gaussian analysis
frameworkwith different levels of covariance definitions. The first
method separately maps sea level and currents with single-scale
covariance functions and leads to estimates of the geostrophic and
ageostrophic circulations. The second maps both measurements
simultaneously and projects the circulation onto 4 contributions:
geostrophic, ageostrophic rotary, ageostrophic divergent and inertial.
When compared to the first method, the second mapping moderately
improves the resolution of geostrophic currents but significantly
improves estimates of the ageostrophic circulation, in particular
near-inertial oscillations. This method offers promising perspectives
for reconstructions of the ocean surface circulation. Even the hourly
dynamics can be reconstructed from measurements made locally every few
days because nearby measurements are coherent enough to help fill the
gaps. Based on numerical simulation of ocean surface currents, the
proposed SKIM mission that combines a nadir altimeter and a Doppler
scatterometer with a 300 km wide swath (with a mean revisit time of 3
days) would allow the reconstruction of 50% of the near-inertial
variance around an 18 hour period of oscillation.