Imaging mesoscale upper ocean dynamics using synthetic aperture radar and optical data

Abstract

A synergetic approach for quantitative analysis of high‐resolution ocean synthetic aperture radar (SAR) and imaging spectrometer data, including the infrared (IR) channels, is suggested. This approach first clearly demonstrates that sea surface roughness anomalies derived from Sun glitter imagery compare very well to SAR roughness anomalies. As further revealed using these fine‐resolution (∼1 km) observations, the derived roughness anomaly fields are spatially correlated with sharp gradients of the sea surface temperature (SST) field. To quantitatively interpret SAR and optical (in visible and IR ranges) images, equations are derived to relate the “surface roughness” signatures to the upper ocean flow characteristics. As developed, a direct link between surface observations and divergence of the sea surface current field is anticipated. From these satellite observations, intense cross‐frontal dynamics and vertical motions are then found to occur near sharp horizontal gradients of the SST field. As a plausible mechanism, it is suggested that interactions of the wind‐driven upper layer with the quasi‐geostrophic current field (via Ekman advective and mixing mechanisms) result in the generation of secondary ageostrophic circulation, producing convergence and divergence of the surface currents. The proposed synergetic approach combining SST, Sun glitter brightness, and radar backscatter anomalies, possibly augmented by other satellite data (e.g., altimetry, scatterometry, ocean color), can thus provide consistent and quantitative determination of the location and intensity of the surface current convergence/divergence (upwelling/downwelling). This, in turn, establishes an important step toward advances in the quantitative interpretation of the upper ocean dynamics from their two‐dimensional satellite surface expressions.