The Significance of the Long-Wavelength Correction for Studies of
Baroclinic Tides with SWOT
Abstract
The long-wavelength correction (LWC) of SWOT data is intended to reduce
errors related to the stability of the SWOT antenna and its attitude in
orbit, especially those errors related to the roll of the satellite.The
algorithms used to compute the LWC utilize SWOT KaRIn sea surface-height
(SSH) measurements and additional data, and the LWC may abosrb
geophysical SSH into the correction. Different LWC algorithms are used
on the L2 and L3 SWOT products, which are analyzed here during the 1-day
repeat (Cal/Val) mission phase lasting approximately 100 days. During
this mission phase the SSH anomaly (SSHA) computed using the L3 LWC is
much more realistic than the L2 LWC, shown here by comparing spatial
statistics of the L2 and L3 products.The L3 LWC algorithm is nonlinear
insofar as it depends on second-order statistics of the SSHA and
multi-satellite SSHA differences, making it difficult to quantify the
extent to which it could absorb baroclinic tidal signals. To overcome
this difficulty, a proxy L3 LWC algorithm is developed which mimics the
L3 LWC but is strictly linear in the SSHA. The proxy LWC is applied to
the predicted internal tide available on the products, and it is found
to absorb roughly 5% to 10% of the variance of the internal tide;
although, this figure varies strongly depending on the magnitude and
orientation of the tidal waves.