Abstract
Measurements of diurnal changes in ocean color in turbid coastal regions in the Gulf of Mexico were characterized using above water spectral radiometry from a National Aeronautics and Space Administration (aerosol robotic network-WaveCIS CSI-06) site that can provide 8 to 10 observations per day. Satellite capability to detect diurnal changes in ocean color was characterized using hourly overlapping afternoon orbits of the visual infrared imaging radiometer suite (VIIRS) Suomi National Polar-orbiting Partnership ocean color sensor and validated with in situ observations. The monthly cycle of diurnal changes was investigated for different water masses using VIIRS overlaps. Results showed the capability of satellite observations to monitor hourly color changes in coastal regions that can be impacted by vertical movement of optical layers, in response to tides, resuspension, and river plume dispersion. The spatial variability of VIIRS diurnal changes showed the occurrence and displacement of phytoplankton blooming and decaying processes. The diurnal change in ocean color was above 20%, which represents a 30% change in chlorophyll-a. Seasonal changes in diurnal ocean color for different water masses suggest differences in summer and winter responses to surface processes. The diurnal changes observed using satellite ocean color can be used to define the following: surface processes associated with biological activity, vertical changes in optical depth, and advection of water masses.
Highlights
The color of ocean water can change rapidly throughout the day, especially in coastal areas where dynamic ocean processes occur.[1]
Our objective is to examine the diurnal changes in ocean color that can occur in coastal regions and determine the capability of the present polar-orbiting satellites to identify and validate these changes
Our objective was to examine the diurnal changes in ocean color that can occur in coastal regions and determine the capability of the present polar orbiting satellites to identify and validate these changes
Summary
The color of ocean water can change rapidly throughout the day, especially in coastal areas where dynamic ocean processes occur.[1] Ocean color is defined as the spectral water-leaving radiance (nLw) or remote sensing reflectance (Rrs) and is used to define water properties including chlorophyll-a and inherent optical properties, such as absorption and scattering.[2,3,4] Changes in the color of the ocean water can occur on daily, hourly, and subhourly scales as a result of (1) advection of water masses, such as fronts and river plumes that respond to wind events, tidal forcing, and dynamic circulation events;[5] (2) water mass bio–geo–optical changes that include the growth and decay of phytoplankton blooms;[6] (3) upwelling and downwelling of vertical optical layers;[7,8,9,10] and (4) particle settling and resuspension events.[11,12,13] The changes in vertical. Diurnal color changes can support how bio-optics is linked to changes in surface temperature and physical processes from circulation models.[3]
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