Relationships between Q-factor and seawater optical properties in a coastal region

The Q-factor-the ratio between upwelling irradiance and upwelling radiance-describes the bidirectional structure of seawater apparent optical properties as a function of geometry and of marine and atmospheric optical characteristics. A 3-yr time series of Q(n)(lambda) measurements-the Q-factor determined by nadir radiance-from the North Adriatic Sea coastal waters, has been analyzed. Scatter plots of Q(n)(lambda) versus sun zenith, theta (0) for different intervals of the diffuse attenuation coefficient K-d(lambda) have shown a consistent exponential trend. In addition, least-squares regressions of Q(n)(lambda) versus Q(n)(490) have exhibited determination coefficients R-2 that vary from 0.77 to 0.94 in the spectral range between 412 and 555 nm and R-2 = 0.50 at 665 nm. To account for these findings, an empirical model for Q(n)(lambda) as a function of theta (0) and K-d(lambda (0)) at the reference wavelength lambda (0) = 490 nm is proposed for North Adriatic coastal waters.