SPECTRAL OF REMOTE SENSING REFLECTANCE OF SURFACE WATERS

Abstract

Spectral measurements of remote sensing reflectance (R_rs) of surface waters in the northeastern Gulf of Mexico were conducted in various seasons in 1999-2000 using Fieldspec Analytical Spectral Devices (ASD) Spectroradiometer. Filtering process was performed on the data to eliminate invalid data. In general, in coastal waters particularly near rivers mouth (water type-2) the R_rs spectrals were relatively low at blue, maximum at green, and decreased to a minimum value at the red wavelength. In offshore waters (type-1), the general pattern of R_rs spectrals were maximum at the blue wavelength and then continued to decline at the green wavelength until the minimum value at the red wavelength except during summer where R_rs spectrals in most offshore area having the maximum value at the green wavelength due to the phytoplankton bloom as a result of freshwater intrusion from the Mississippi river. In general, the patterns and values of R_rs ​​were significantly different among seasons and locations. Results showed that R_rs values ​​at the blue wavelength (λ=400 nm) were generally higher in the spring than in other seasons ranging of 0.007-0.018 sr^-1 in offshore waters and 0.004-0.015 sr^-1 in coastal waters. During spring, Rrs values at the green ​​wavelength (λ=500 nm) were also higher than in other seasons ​​ranging of 0.005-0.013 sr^-1 found in coastal waters. However, during summer in coastal waters, the maximum values of R_rs spectrals were found in different green wavelength on different locations showed the differences in the type and composition of phytoplankton, organic materials, and suspension matters at those locations.

Keywords: remote sensing reflectance, phytoplankton, offshore, coastal, Gulf of Mexico