Quantifying sargassum boundaries on eastern and western walls of the gulf stream protruding near cape hatteras into Sargasso Sea Bermuda/Azores

摘要

The Sargasso Sea has been a ocean life habitat for millions of years, yet accurate assessment of the boundary area and detection of these relatively small sea surface features using Landsat series and Moderate resolution Imaging Spectroradiometer (MODIS) instruments have been found to have difficulty or even impossible due to lack of spatial resolution, coverage, recurring observance, and algorithm limitations to identify pelagic species of Sargassum. Sargassum rafts tend to be elongated, curved in the upwind direction and warmer than the surrounding ocean surface. Long weed `trails' extending upwind from the rafts are evidence of plants dropping out and being left behind. Satellite data utilizing a simple ocean color indexes such as the floating algae Index and Normalized Differential Vegetation Index (NDVI) have been established to detect floating algae in open environments using MODIS instruments. Floating Algae Index (FAI) has shown advantages over the traditional NDVI and Enhanced Vegetation Index (EVI) because FAI is less sensitive to changes in environmental and observing conditions (aerosol type and thickness, solar/viewing geometry, and sun glint) and can see through thin clouds. The baseline subtraction method provides a simple yet effective means for atmospheric correction. The algorithms assisted in identifying the boundary area of the Sargasso Sea and the path of this floating alga past Cape Hatteras into the Atlantic Ocean. Due to the fact that similar spectral bands are available on many existing and planned satellite sensors such as Landsat series observations satellites, the NDVI and FIA concept was extendable to establish a long-term record of these ecologically biological dependent ocean plants.