Kowalczuk, P, Darecki, M, Zablocka, M, Gorecka, I (2010). 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. OCEANOLOGIA, 52(2), 171-196.
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 at 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 Gdansk close to the Vistula River mouth were eliminated from the data set. The calculated errors in the estimation of a(CDOM) (400) in the first phase of the analysis were Bias = -0.02, RMSE = 0.46 and R-2 = 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 a(CDOM) (400), based on SeaWiFS data, were Bias = -0.02, RMSE = 0.23 and R-2 = 0.40. The validation of the Kowalczuk et al. (2005) empirical algorithm applied to MODIS data led to a less accurate estimate of a(CDOM)(400): Bias = -0.03, RMSE = 0.19 and R-2 = 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 a(CDOM)(400) in the Baltic Sea between 2004 and 2008.