Apparent optical properties of the Canadian Beaufort Sea – Part 2: The 1% and 1 cm perspective in deriving and validating AOP data products

[摘要] A next-generation in-water profiler designed to measure the apparent opticalproperties (AOPs) of seawater was developed and validated across a widedynamic range of in-water properties. The new free-falling instrument, theCompact-Optical Profiling System (C-OPS), was based on sensors built witha cluster of 19 state-of-the-art microradiometers spanning 320–780 nm anda novel kite-shaped backplane. The new backplane includes tunableballast, a hydrobaric buoyancy chamber, plus pitch and rolladjustments, to provide unprecedented stability and vertical resolution innear-surface waters. A unique data set was collected as part of thedevelopment activity plus the first major field campaign that used the newinstrument, the Malina expedition to the Beaufort Sea in the vicinity of theMackenzie River outflow. The data were of sufficient resolution and qualityto show that errors – more correctly, uncertainties – in the execution ofdata sampling protocols were measurable at the 1% and 1 cm level withC-OPS. A theoretical sensitivity analysis as a function of three water typesestablished by the peak in the remote sensing reflectance spectrum,R_rs(λ), revealed which water types and which parts of thespectrum were the most sensitive to data acquisition uncertainties. Shallowriverine waters were the most sensitive water type, and the ultraviolet andnear-infrared spectral end members, which are critical tonext-generation satellite missions, were the most sensitive parts of thespectrum. The sensitivity analysis also showed how the use of data productsbased on band ratios significantly mitigated the influence of dataacquisition uncertainties. The unprecedented vertical resolution providedhigh-quality data products, which supported an alternative classificationcapability based on the spectral diffuse attenuation coefficient,K_d(λ). The K_d(320) and K_d(780)data showed how complex coastal systems can be distinguishedtwo-dimensionally and how near-ice water masses are different from theneighboring open ocean. Finally, an algorithm for predicting the spectralabsorption due to colored dissolved organic matter (CDOM), denoteda_CDOM(λ), was developed using theK_d(320) / K_d(780) ratio, which was based ona linear relationship with respect to a_CDOM(440). The robustnessof the approach was established by expanding the use of the algorithm toinclude a geographically different coastal environment, the SouthernMid-Atlantic Bight, with no significant change in accuracy (approximately98% of the variance explained). Alternative spectral end membersreminiscent of next-generation (340 and 710 nm) as well as legacy satellitemissions (412 and 670 nm) were also used to accurately derive a_CDOM(440) from Kd

[学科分类] 地球化学与岩石