title: Radiance transmittance measured at the ocean surface.
abstract: The radiance transmittance (Tr) is the ratio of the water-leaving radiance (Lw(0+)) to the sub-surface upwelling radiance (Lu(0-)), which is an important optical parameter for ocean optics and ocean color remote sensing. Historically, a constant value (~0.54) based on theoretical presumptions has been adopted for Tr and is widely used. This optical parameter, however, has never been measured in the aquatic environments. With a robust setup to measure both Lu(0-) and Lw(0+) simultaneously in the field, this study presents Tr in the zenith direction between 350 and 700 nm measured in a wide range of oceanic waters. It is found that the measured Tr values are generally consistent with the long-standing theoretical value of 0.54, with mean relative difference less than 10%. In particular, the agreement within the spectral domain of 400-600 nm is found to be the best (with the averaged difference less than 5%). The largest difference is observed for wavelengths longer than 600 nm with the average difference less than 15%, which is related to the generally very small values in both Lu(0-) and Lw(0+) and rough environmental conditions. These results provide a validation of the setup for simultaneous measurements of upwelling radiance and water-leaving radiance and confidence in the theoretical Tr value used in ocean optics studies at least for oceanic waters.
authors.forename: Jianwei
authors.initials: J
authors.lastname: Wei
authors.forename: Zhongping
authors.initials: Z
authors.lastname: Lee
authors.forename: Marlon
authors.initials: M
authors.lastname: Lewis
authors.forename: Nima
authors.initials: N
authors.lastname: Pahlevan
authors.forename: Michael
authors.initials: M
authors.lastname: Ondrusek
authors.forename: Roy
authors.initials: R
authors.lastname: Armstrong