Scientific objectives: surface currents, waves & sea ice drift

The main objective of SKIM 

is to measure the total surface current vectors (TSCV). Each word here is important: the total velocity is the velocity of actual water parcels averaged over a few minutes (snapshots would include much stronger wind-wave signatures). This differs from altimeter-derived currents that generally miss most of the current variance. Because SKIM includes a classic altimeter, it will be able to bridge the gap between today's measurements and the more complete assessment of the TCSV. Vector current measurement on a single pass would be a first time ever measurement from space: previous ATI or Doppler centroid (as on this Envisat image) only give the current component perpendicular to the satellite track. Measurements of current shall be over the global ice-free and precipitation-free ocean and inland seas from 82°S to 82°N at a spatial resolution of ≤40 km (equivalent wavelength of ≤80 km) with a revisit of ≤ 10 days and a standard uncertainty of ≤0.1 m/s for each component.

Another important objective is to measure and investigate the directional wave spectrum simultaneously with TSCV at a gridded spatial resolution of ≤70 km. One motivation for the wave measurement is the correction of the important wave-induced Doppler velocity bias. As a result an accurate measurement of the current requires an accurate characterization of the wave field. This wave bias is characterized by a surface Stokes drift vector that is amplified by the sensitivity of the radar to surface slopes. This same Stokes drift is also a very important component of the average drift velocity of

water and floatsam. SKIM will be unique in measuring this component of the surface current vector.

Over sea ice, SKIM will measure sea ice motion and characterise the wave-TSCV-sea ice interaction (i.e. break-up, growth, kinematics) at sub-daily timescales together with collocated surface characteristics (e.g. sea ice thickness, dynamic ocean topography) from the nadir-pointing beam.

A particular area of interest for the TCSV is the the Equatorial ocean, including equatorial wave dynamics (Kelvin waves, Tropical Instability waves ...), upwelling, at intra-seasonal to inter-annual time scales. This is where altimetry captures very little of the ocean dynamics.

All these measurements will characterise and quantify ocean surface kinematics (i.e. waves, fronts, large-scale TSCV) and their impact on multi-scale ocean-atmosphere exchange of momentum, heat, mass, carbon dioxide (and other climatically important gases) in complex heterogeneous regions (e.g. polar regions continental shelves, large frontal regions).