An Algorithm to Determine the Slope of the Spectral Absorption of Colored Dissolved Organic Matter (CDOM) and Detritus

A simple method to determine the slope of spectral variations of combined absorption of the colored dissolved organic matter and detritus (CDM) is presented. This method uses the slope of total absorption spectrum excluding contribution of waters in lieu of slope for the CDM. The errors in slopes using the new method decreased with increase in contributions of CDM to the total absorption. The relative errors were less than 10% when CDM contributions were above 60% and even at very low contributions of CDM of 25%, errors in the slopes were less than 40%. For estuarine and coastal waters rich in CDM, the errors in the slopes for CDM were less than 10% using this simple method. Absorption of CDM derived using the slope with the new method in a semi-analytical algorithm QAAV6 showed improved performance with RMSE of 0.07, 0.0119 and 0.0027 at 405, 555 and 665 nm respectively and with R² > 0.95 at all spectral range. The method provided values of spectral absorption due to CDM with fewer errors when validated with the satellite derived data from MODIS and SeaWiFS. This method to determine the slope of CDM could be easily implemented in any model, as it was very generic in nature, simple, did not involve any mathematical model and avoids empirical methods. Since the method is also independent of any specific bands, it can be used for most ocean color satellites. Considering the performance of this new method and applicability for most water types, it was considered as a better option to derive the slope of CDM than using a constant value or deriving the slope with empirical method.