Characterizing the vertical diffuse attenuation coefficient for downwelling irradiance in coastal waters: Implications for water penetration by high resolution satellite data

To characterize the water column, the diffuse attenuation coefficient of downwelling irradiance, Kd(z, λ) (m− 1) is one of the most important optical properties of seawater. The purpose of this research was to determine the downwelling diffuse attenuation coefficient of water around Roatan Island, Honduras. In situ Kd analysis showed low attenuation coefficient values in green and blue and increased exponentially after 570 nm. The blue, green and red portion of the spectrum showed a Kd value of 0.138, 0.158, and 0.503 m− 1, respectively. Error analysis revealed a significantly high uncertainty in the red region (600-700 nm) and, as expected, low estimation uncertainty in blue and green. When compared with IKONOS derived Kd (490 nm), it was observed that the differences were negligible, being 0.0084 and 0.0054 m− 1 for station #1 and #2, respectively. Based on the fact that 90% of the diffused reflected light from a water body comes from a surface layer of water of depth 1 / Kd, the results showed that a typical satellite sensor (such as IKONOS) can penetrate up to 8 m in the blue band, 6 m in green, and 2 m in the red region.