Validation of empirical and semi-analytical remote sensing algorithms for estimating absorption by Coloured Dissolved Organic Matter in the Baltic Sea from SeaWiFS and MODIS imagery
Validation of empirical and semi-analytical remote sensing algorithms for estimating absorption by Coloured Dissolved Organic Matter in the Baltic Sea from SeaWiFS and MODIS imagery
An extensive bio-optical data set obtained from field measurements was used to
evaluate the performance of an empirical (Kowalczuk et al. 2005) and two semi-
analytical algorithms: Carder et al. (1999) and GSM01 (Maritorena et al. 2002) for
estimating CDOM absorption in the Baltic Sea. The data set includes coincident
measurements of radiometric quantities and absorption coefficients of CDOM made during 43 cruises between 2000 and 2008. In the first stage of the analysis, the
accuracy of the empirical algorithm by Kowalczuk et al. (2005) was assessed using
in situ measurements of remote sensing reflectance. Validation results improved
when matching points located in Gulf of Gdańsk close to the Vistula River mouth
were eliminated from the data set. The calculated errors in the estimation of
aCDOM(400) in the first phase of the analysis were Bias = −0.02, RMSE = 0.46
and R2 = 0.70. In the second stage, the empirical algorithm was tested on satellite
data from SeaWiFS and MODIS imagery. The satellite data were corrected
atmospherically with the MUMM algorithm designed for turbid coastal and inland
waters and implemented in the SeaDAS software. The results of the best case
scenario for estimating the CDOM absorption coefficient aCDOM(400), based on
SeaWiFS data, were Bias = −0.02, RMSE = 0.23 and R2 = 0.40. The validation
of the Kowalczuk et al. (2005) empirical algorithm applied to MODIS data led
to a less accurate estimate of aCDOM(400): Bias = −0.03, RMSE = 0.19 and
R2 = 0.29. This assessment of the accuracy of standard semi-analytical algorithms
available in the SeaWiFS and MODIS imagery processing software revealed that
both algorithms (GSM 01 and Carder) underestimate CDOM absorption in the
Baltic Sea with mean systematic and random errors in excess of 70%. The paper
presents examples of the application of the Kowalczuk et al. (2005) empirical
algorithm for producing maps of the seasonal distribution of aCDOM(400) in the
Baltic Sea between 2004 and 2008.
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