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| Titel |
Apparent optical properties of the Canadian Beaufort Sea – Part 2: The 1% and 1 cm perspective in deriving and validating AOP data products |
| VerfasserIn |
S. B. Hooker, J. H. Morrow, A. Matsuoka |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 10, no. 7 ; Nr. 10, no. 7 (2013-07-04), S.4511-4527 |
| Datensatznummer |
250018327
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| Publikation (Nr.) |
 copernicus.org/bg-10-4511-2013.pdf |
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| Zusammenfassung |
| A next-generation in-water profiler designed to measure the apparent optical
properties (AOPs) of seawater was developed and validated across a wide
dynamic range of in-water properties. The new free-falling instrument, the
Compact-Optical Profiling System (C-OPS), was based on sensors built with
a cluster of 19 state-of-the-art microradiometers spanning 320–780 nm and
a novel kite-shaped backplane. The new backplane includes tunable
ballast, a hydrobaric buoyancy chamber, plus pitch and roll
adjustments, to provide unprecedented stability and vertical resolution in
near-surface waters. A unique data set was collected as part of the
development activity plus the first major field campaign that used the new
instrument, the Malina expedition to the Beaufort Sea in the vicinity of the
Mackenzie River outflow. The data were of sufficient resolution and quality
to show that errors – more correctly, uncertainties – in the execution of
data sampling protocols were measurable at the 1% and 1 cm level with
C-OPS. A theoretical sensitivity analysis as a function of three water types
established by the peak in the remote sensing reflectance spectrum,
Rrs(λ), revealed which water types and which parts of the
spectrum were the most sensitive to data acquisition uncertainties. Shallow
riverine waters were the most sensitive water type, and the ultraviolet and
near-infrared spectral end members, which are critical to
next-generation satellite missions, were the most sensitive parts of the
spectrum. The sensitivity analysis also showed how the use of data products
based on band ratios significantly mitigated the influence of data
acquisition uncertainties. The unprecedented vertical resolution provided
high-quality data products, which supported an alternative classification
capability based on the spectral diffuse attenuation coefficient,
Kd(λ). The Kd(320) and Kd(780)
data showed how complex coastal systems can be distinguished
two-dimensionally and how near-ice water masses are different from the
neighboring open ocean. Finally, an algorithm for predicting the spectral
absorption due to colored dissolved organic matter (CDOM), denoted
aCDOM(λ), was developed using the
Kd(320) / Kd(780) ratio, which was based on
a linear relationship with respect to aCDOM(440). The robustness
of the approach was established by expanding the use of the algorithm to
include a geographically different coastal environment, the Southern
Mid-Atlantic Bight, with no significant change in accuracy (approximately
98% of the variance explained). Alternative spectral end members
reminiscent of next-generation (340 and 710 nm) as well as legacy satellite
missions (412 and 670 nm) were also used to accurately derive
aCDOM(440) from Kd
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