Abstract
Through the analysis of hyperspectral imaging data collected over water surfaces covered by floating vegetation, such as Sargassum and algae, we observed that the spectra commonly contain a reflectance peak centered near 1.07 μm. This peak results from the competing effects between the well-known vegetation reflectance plateau in the 0.81–1.3 μm spectral range and the absorption effects above 0.75 μm by liquid water within the vegetation and in the surrounding water bodies. In this article, we propose a new index, namely the floating vegetation index (FVI), for the hyperspectral remote sensing of vegetation over surface layers of oceans and inland lakes. In the formulation of the FVI, one channel centered near 1.0 μm and another 1.24 μm are used to form a linear baseline. The reflectance value of the third channel centered at the 1.07-μm reflectance peak above the baseline is defined as the FVI. Hyperspectral imaging data acquired with the AVIRIS (Airborne Visible Infrared Imaging Spectrometer) instrument over the Gulf of Mexico and over salt ponds near Moffett Field in southern portions of the San Francisco Bay were used to demonstrate the success in detecting Sargassum and floating algae with this index. It is expected that the use of this index for the global detection of floating vegetation from hyperspectral imaging data to be acquired with future satellite sensors will result in improved detection and therefore enhanced capability in estimating primary production, a measure of how much carbon is fixed per unit area per day by oceans and inland lakes.
Highlights
Multi-channel satellite instruments, such as MODIS (Moderate Resolution Imaging Spectroradiometer) [1,2], MERIS (Medium Resolution Imaging Spectrometer) [3], SeaWiFS (Sea-Viewing Wide Field-of-View Sensor) [4], VIIRS (Visible Infrared Imaging Radiometer Suite) [5], and OLCI (Ocean and Land Color Instrument) [6], were designed for remote sensing of ocean color over open ocean waters
We propose a new index, namely the floating vegetation index (FVI), for the hyperspectral remote sensing of vegetation, regardless of green, red, or brown colored vegetation, floating on the water surfaces of oceans and inland lakes
We use a specific AVIRIS data set acquired over salt evaporation ponds in the southern portion of the San Francisco Bay at UTC 20:21:00 on 26 August 2009 to illustrate the FVI concept and the deficiency of the red channels used in the formation of the MODIS FAI and MERIS MCI indices
Summary
Multi-channel satellite instruments, such as MODIS (Moderate Resolution Imaging Spectroradiometer) [1,2], MERIS (Medium Resolution Imaging Spectrometer) [3], SeaWiFS (Sea-Viewing Wide Field-of-View Sensor) [4], VIIRS (Visible Infrared Imaging Radiometer Suite) [5], and OLCI (Ocean and Land Color Instrument) [6], were designed for remote sensing of ocean color over open ocean waters. The retrieving algorithms for these instruments were mainly designed for the derivation of ocean constitutes suspended or dissolved in water, such as chlorophyll-a (Chl-a) concentration, absorption coefficients of colored dissolved organic matter (CDOM), and diffuse attenuation coefficient. The Chl-a data product does not fully include the chlorophyll-a contained in vegetation floating on water surfaces due to the fact that relevant bright pixels are frequently masked out prior to Chl-a retrieval. The use of the standard Chl-a data product for the derivation of ocean primary production can, result in an underestimation of primary production (which is a measure of carbon fixing rate per unit area per day). 2f0c1a8,r1b0o, n14f2i1xing rate per unit area per day). Algae bloom cases, floating vegetation can cover a large portion of a gInivceenrtwaiantesritauraetaio.
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