A Combination of Spatial Domain Filters to Detect Surface Ocean Current from Multi-Sensor Remote Sensing Data

Mohammed Abdul Athick As,Shih-Yu Lee

doi:10.3390/rs14020332

Abstract

This research investigates the applicability of combining spatial filter’s algorithm to extract surface ocean current. Accordingly, the raster filters were tested on 80–13,505 daily images to detect Kuroshio Current (KC) on weekly, seasonal, and climatological scales. The selected raster filters are convolution, Laplacian, north gradient, sharpening, min/max, histogram equalization, standard deviation, and natural break. In addition, conventional data set of sea surface currents, sea surface temperature (SST), sea surface height (SSH), and non-conventional data such as total heat flux, surface density (SSD), and salinity (SSS) were employed. Moreover, controversial data on ocean color are included because very few studies revealed that chlorophyll-α is a proxy to SST in the summer to extract KC. Interestingly, the performance of filters is uniform and thriving for seasonal and on a climatological scale only by combining the algorithms. In contrast, the typical scenario of identifying Kuroshio signatures using an individual filter and by designating a value spectrum is inapplicable for specific seasons and data set. Furthermore, the KC’s centerlines computed from SST, SSH, total heat flux, SSS, SSD, and chlorophyll-α correlate with sea surface currents. Deviations are observed in the various segments of Kuroshio’s centerline extracted from heat flux, chlorophyll-α, and SSS flowing across Tokara Strait from northeast Taiwan to the south of Japan.

Highlights

The recent advancements in satellite sensors and their algorithms have archived coherent, reliable, and high-resolution global oceanographic data for many decades
Defining isotherm could not detect during summer as Kuroshio Current (KC) wears off due to uniform sea surface heating
We regenerated the results as per the algorithms proposed by Liu and Hou for detecting Kuroshio front from sea surface temperature (SST) and chlorophyll-α [18] using a range between 25–27 ◦ C

Summary

Introduction

The recent advancements in satellite sensors and their algorithms have archived coherent, reliable, and high-resolution global oceanographic data for many decades. The characteristics of Kuroshio water differ from those of its surroundings, and it forms a clear distinguished front of biophysical parameters such as SST, SSS, and chlorophyll-α [3,4]. As warm and saline water is brought into the study region (Figure 1) from the tropical pacific ocean, the SST and SSS of Kuroshio are higher than their surrounding waters. Precise temperature and salinity boundaries formed at the north and western edges of the Kuroshio axis [5]. Satellite-based remote sensing from various sensors provides valuable knowledge for current ocean investigations

Methods

Results

Discussion

Conclusion