Arctic Sea Ice Drift Measured by Shipboard Marine Radar

This study presents Arctic sea ice drift fields measured by shipboard marine X-band radar (MR). The measurements are based on the maximum cross correlation between two sequential MR backscatter images separated ∼1 min in time, a method that is commonly used to estimate sea ice drift from satellite products. The advantage of MR is that images in close temporal proximity are readily available. A typical MR antenna rotation period is ∼1–2 s, whereas satellite revisit times can be on the order of days. The technique is applied to ∼4 weeks of measurements taken from R/V Sikuliaq in the Beaufort Sea in the fall of 2015. The resulting sea ice velocity fields have ∼500 m and up to ∼5 min resolution, covering a maximum range of ∼4 km. The MR velocity fields are validated using the GPS-tracked motion of Surface Wave Instrument Float with Tracking (SWIFT) drifters, wave buoys, and R/V Sikuliaq during ice stations. The comparison between MR and reference sea ice drift measurements yields root-mean-square errors from 0.8 to 5.6 cm s⁻¹. The MR sea ice velocity fields near the ice edge reveal strong horizontal gradients and peak speeds > 1 m s⁻¹. The observed submesoscale sea ice drift processes include an eddy with ∼6 km diameter and vorticities <–2 (normalized by the Coriolis frequency) as well as converging and diverging flow with normalized divergences <–2 and >1, respectively. The sea ice drift speed correlates only weakly with the wind speed (r² = 0.34), which presents a challenge to conventional wisdom.