Validation of a spectral correction procedure for sun and sky reflections in above-water reflectance measurements

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Groetsch, Philipp M.M. ; Gege, Peter ; Simis, Stefan G.H. ; Eleveld, Marieke A. ; Peters, Steef W.M. (2017)
  • Publisher: dsfsdf
  • Related identifiers: doi: 10.1364/oe.25.00a742
  • Subject: Institut für Methodik der Fernerkundung | EA0 | Experimentelle Verfahren

A three-component reflectance model (3C) is applied to above-water radiometric measurements to derive remote-sensing reflectance Rrs(l). 3C provides a spectrally resolved offset D(l) to correct for residual sun and sky radiance (Rayleigh- and aerosol-scattered) reflections on the water surface that were not represented by sky radiance measurements. 3C is validated with a data set of matching above- and below-water radiometric measurements collected in the Baltic Sea, and compared against a scalar offset correction D. Correction with D(l) instead of D consistently reduced the (mean normalized root-mean-square) deviation between Rrs(l) and reference reflectances to comparable levels for clear (D: 14.3 +- 2.5 %, D(l): 8.2 +- 1.7 %), partly clouded (D: 15.4 +- 2.1 %, D(l): 6.5 +- 1.4 %), and completely overcast (D: 10.8 +- 1.7 %, D(l): 6.3 +- 1.8 %) sky conditions. The improvement was most pronounced under inhomogeneous sky conditions when measurements of sky radiance tend to be less representative of surface-reflected radiance.Accounting for both sun glint and sky reflections also relaxes constraints on measurement geometry, which was demonstrated based on a semi-continuous daytime data set recorded in an eutrophic freshwater lake in the Netherlands. Rrs(l) that were derived throughout the day varied spectrally by less than 2 % relative standard deviation. Implications on measurement protocols are discussed. An open source software library for processing reflectance measurements was developed and is made publicly available.
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