Improving Surface Current Estimation From Geostationary Ocean Color Imager Using Tidal Ellipse and Angular Limitation

Abstract

Sea surface currents (SSCs) in coastal regions can be mapped from successive optical images observed by satellite. We implemented the maximum cross‐correlation (MCC) algorithm to Geostationary Ocean Color Imager‐derived total suspended matter in the East China Sea in this study. We developed a new data filtering method to improve the accuracy of SSC vector sequence using estimated tidal ellipse. The proposed method eliminated spurious vectors by considering direction order and suitable angular limitation. The obtained average velocity of SSC reached 0.72 m/s, which was close to the buoy‐measured average speed of 0.64 m/s. Compared with existing spurious vector eliminating method, the average angular error was improved significantly by 28–38% and the average relative magnitude error was improved by 3% in the case study.

An Objective Method with a Continuity Constraint for Improving Surface Velocity Estimates from the Geostationary Ocean Color Imager

“…Previous studies suggested the existence of many unrealistic velocity vectors in MCCderived surface currents [2,7]. Great efforts are made to eliminate erroneous vectors using various techniques [6,9,30].…”

“…The MCC method is commonly used to estimate hourly total surface currents from the sequential tracer images [4,6,7,10,12,13]. Briefly, a sub-source box in an initial image is cross-correlated with the same size box in a subsequent image, searching for the most likely location in the second image by the maximum cross-correlation coefficient.…”

“…Traditional direct measurements of surface currents are both time-and cost-consuming, and it is impossible to obtain two-dimensional, continuous surface current fields with wide coverage. The prospect of observing nearly instantaneous surface velocity fields without temporal aliasing over a large area has prompted numerous attempts to infer advective surface currents directly from sequential satellite imagery [1][2][3][4][5][6][7].…”

“…The Geostationary Ocean Color Imager (GOCI), on the other hand, could provide up to eight hourly snapshots per day with a spatial resolution of 500 m [11]. The unprecedented GOCI capability is adequate for deriving changing surface currents in the China seas (here referring to the Bohai Sea, Yellow Sea (YS), and East China Sea (ECS)) where the tidal currents dominate [7,10,[12][13][14][15][16][17][18]. Substantial efforts have been carried out to retrieve the hourly variability of surface currents using various GOCI-derived hourly ocean color products, such as total suspended matter (TSM) [13,15,17], chlorophyll a [4,6], normalized water-leaving radiances, and a diffuse attenuation coefficient [10,12].…”