Spatial Distribution and Variability of Total Scattering Coefficient in Surface Water of Various Season

Abstract

The optical properties of the waters are affected by the intensity and angle of incidence light and material contained in the water column. The optical properties are divided into two categories i.e., apparent optical properties (AOP) influenced by the intensity and angle of incident light and the amount of material in the water, and the inherent optical properties (IOP) affected only by the content of the material in the column water such as phytoplankton, suspended solid materials, organic matter, and colored dissolved organic matter (colored dissolved organic matter (CDOM). Scattering is the process of radiation deflection by the water column and the material contained in the water column. Scattering is divided into two categories i.e., backscattering and forward scattering. Total scattering is a combination of backscattering and forward scattering. The Northeastern Gulf of Mexico waters (NEGOM) contains type-1 waters (offshore) and type-2 (coastal waters). The NEGOM waters are also influenced by the Loop Current, upwelling, wind, and freshwater discharge of several rivers. Currently, few studies were conducted related variability and spatial distribution of the total scattering in NEGOM waters especially in tropical waters. Standard facilities and bio-optical equipment are also minimal to none in Indonesia. Therefore, this research is very important to be conducted. The purpose of this study was to determine the variability of the spatial and temporal distribution of the total scattering coefficient (scattering) in 9 wavelength (λ) in different seasons in the NEGOM. The result was expected to obtain information about the value, variability, and the spatial distribution of the total scattering coefficient (scattering) which will be utilized in the development of bio-optical algorithms satellite ocean color. The results showed that the total scattering coefficient in 1999 (average of 0.26(±0.05)-0.37(± 0.07) m-1), was generally higher in the summer than that in spring and winter (average of 0.09(±0.002)-0.23(±0.04) m-1). Except in the Mississippi region, the total scattering coefficient in spring 1999 (average of 1.54(±0.94)-2.01(±1.03) m-1) was higher than that in summer and winter. In 2000, total scattering coefficient values were also generally higher in summer (average of 0.21(±0.02)-0.32(±0.02) m-1) than that in spring and winter (average of 0.03(±0.003)-0.21(±0.01) m-1. These results showed that particles and suspended matter in summer were generally higher than that in spring and winter. In general, total scattering coefficients were relatively high especially in the coastal waters near the reiver mouth and relatively low in offshore waters in every season except during the summer the total scattering coefficients were relatively high in offshore waters. The relatively high total scattering coefficients found in offshore during summer was caused by the intrusion of the Mississippi river flow toward offshore containing high nutrients that can enhance the growth of phytoplankton in the waters offshore, increase suspended matter, and reduce salinity. The average value of total scattering coefficients at each local coastal and offshore waters in the NEGOM each season were also showed significantly different results.