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Inverse modeling of case-2 waters: Error sources and error propagation

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Inverse Modeling of case-2 waters Inverse modeling of case-2 waters > P. Gege > 15 April 2009 Inverse modeling of case-2 waters: Error sources and error propagation Peter Gege MICAS Expert Working Group, Wageningen, 15 April 2009 Folie 2 Inverse modeling of case-2 waters > P. Gege > 15 April 2009 Overview Case 2 model Error sources Error propagation Error ranking Consequences for fit strategy Folie 3 Inverse modeling of case-2 waters > P. Gege > 15 April 2009 Model: Optically deep case-2 water Irradiance reflectance Backscattering bb(λ) = bb,W(λ) + X · bb,X* · (λ/500)n Absorption a(λ) = aW(λ) + Y · exp[–S · (λ–440)] + C · aP*(λ) bb,W(λ) = 0.00111 · (λ/500)–4.32 = backscattering coefficient of pure water (m–1) bb,X* = 0.0086 m2 g−1 = specific backscattering coefficient of suspended matter at 500 nm aW(λ) = absorption of pure water (from: H. Buiteveld, J. H. M. Hakvoort, M. Donze: The optical properties of pure water. SPIE Vol. 2258, Ocean Optics XII, 1994, p. 174-183) aP*(λ) = specific absorption of phytoplankton . )(b)(a )(bf)(R b b λ+λ λ⋅=λ Gordon et al. (1975) The model considers 3 water constituents (WCs): Phytoplankton, Gelbstoff, Suspended Matter. H. R. Gordon, O. B. Brown, M. M. Jacobs (1975): Computed Relationships between the Inherent and Apparent Optical Properties of a Flat Homogeneous Ocean. Applied Optics 14, 417-427. WASI Folie 4 Inverse modeling of case-2 waters > P. Gege > 15 April 2009 Model: Variability of R(λ) Folie 5 Inverse modeling of case-2 waters > P. Gege > 15 April 2009 Error source: Ambiguities Ambiguity: different parameter combinations yield similar spectra Problem increases drastically with number of fit parameters Æ keep it as low as possible Curve C Y S A 2 µg/l 0.200 m-1 0.0140 nm-1 B 1 µg/l 0.232 m-1 0.0124 nm-1 C 4 µg/l 0.132 m-1 0.0200 nm-1 P. Gege, A. Albert (2006): A tool for inverse modeling of spectral measurements in deep and shallow waters. In: L.L. R

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