Despite the importance of the optical properties such as the downwelling diffuse attenuation coefficient for characterizing the upper water column, until recently no in situ optical measurements were published for the Red Sea. Kirby et al. used observations from the Coastal Zone Color Scanner to characterize the spatial and temporal variability of the diffuse attenuation coefficient (K_d(490)) in the Red Sea. To better understand optical variability and its utility in the Red Sea, it is imperative to comprehend the diffuse attenuation coefficient and its relationship with in situ properties. Two apparent optical properties, spectral remote sensing reflectance (R_rs) and the downwelling diffuse attenuation coefficient (K_d), are calculated from vertical profile measurements of downwelling irradiance (E_d) and upwelling radiance (L_u). K_d characterizes light penetration into water column that is important for understanding both the physical and biogeochemical environment, including water quality and the health of ocean environment. Our study tests the performance of the existing K_d(490) algorithms in the Red Sea and compares them against direct in situ measurements within various subdivisions of the Red Sea. Most standard algorithms either overestimated or underestimated with the measured in situ values of K_d. Consequently, these algorithms provided poor retrieval of K_d(490) for the Red Sea. Random errors were high for all algorithms and the correlation coefficients (r²) with in situ measurements were quite low. Hence, these algorithms may not be suitable for the Red Sea. Overall, statistical analyses of the various algorithms indicated that the existing algorithms are inadequate for the Red Sea. The present study suggests that reparameterizing existing algorithms or developing new regional algorithms is required to improve retrieval of K_d(490) for the Red Sea.

Date Published: 7 May 2016
PDF: 6 pages
Proc. SPIE 9878, Remote Sensing of the Oceans and Inland Waters: Techniques, Applications, and Challenges, 987804 (7 May 2016); doi: 10.1117/12.2222823

Published in SPIE Proceedings Vol. 9878:
Remote Sensing of the Oceans and Inland Waters: Techniques, Applications, and Challenges
Robert J. Frouin; Satheesh C. Shenoi; K. H. Rao, Editor(s)