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

Zibordi, Giuseppe, Jean-François Berthon

Limnol. Oceanogr., 46(5), 2001, 1130-1140 | DOI: 10.4319/lo.2001.46.5.1130

ABSTRACT: 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(λ) measurements—the Q-factor determined by nadir radiance—from the North Adriatic Sea coastal waters, has been analyzed. Scatter plots of Qn(λ) versus sun zenith, ₀, for different intervals of the diffuse attenuation coefficient Kd(λ) have shown a consistent exponential trend. In addition, leastsquares regressions of Q_n(λ) versus Q_n(490) have exhibited determination coefficients R² that vary from 0.77 to 0.94 in the spectral range between 412 and 555 nm and R² = 0.50 at 665 nm. To account for these findings, an empirical model for Qn(λ) as a function of ₀ and K_d(λ₀) at the reference wavelength λ₀ = 490 nm is proposed for North Adriatic coastal waters.