An Evaluation of Radiometric Products from Fixed-Depth and Continuous In-Water Profile Data from Moderately Complex Waters

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Abstract

Radiometricproductsdetermined fromfixed-depthandcontinuousin-waterprofiledatacollected at a coastal site characterized bymoderatelycomplexwaterswere compared to investigate differences and limitations between the two measurement methods. The analysis focused on measurements performed with the same radiometer system sequentially deployed at discrete depths (i.e., 1 and 3m) and successively used toprofilethewatercolumn. Within the 412-2683-nm spectral interval, comparisons show uncertainties of 2% 24%, 3% 25%, and 2% for the subsurface values of upwelling radiance, L-un, upward irradiance, E-un, and downward irradiance, E-dn, all normalized with respect to the above-waterdownward irradiance. The related spectral biases vary from -2% to 1% for L-un, are in the range of 2%-3% for E-un, and are lower than 0.5% for E-dn. Derivedproductslike the irradiance reflectance, R, Q factor at nadir, Q, and normalizedwaterleaving radiance, L-WN, exhibit spectral uncertainties of 4%-6%, 2%-3%, and 2% 24%. The related spectral biases vary from 1% to 3%, 2% to 3%, and 22% to 1%, respectively. An analysis of these results indicates a general diminishing of uncertainties and biases with a decrease of the diffuse attenuation coefficient, K-d, determined at 490 nm, for most of the quantities investigated. Exceptions are E-dn and K-d because an increase of K-d reduces the perturbations due to wave effects on downward irradiance measurements. Anevaluationof the perturbing effects due to the presence of optical stratifications, which lead to a nonlinear decrease with depth of log-transformedradiometricmeasurements, shows an expected increase in uncertainty and bias specifically evident for K-u, E-un, K-l, and L-un, and derived quantities like R, Q, and L-WN. Overall results, supported by a t-test analysis, indicate the possibility of using moorings inmoderatelycomplexcoastalwatersto determine L-WN with a slightly higher uncertainty with respect to that achievable withcontinuousprofiling systems.
Original languageUnknown
Pages (from-to)91-106
JournalJOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY
Volume26
Issue numberNA
DOIs
Publication statusPublished - 1 Jan 2009

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