An empirical algorithm for light absorption by ocean water based on color

Empirical algorithms for the total absorption coefficient and absorption coefficient by pigments for surface waters at 440 nm were developed by applying a quadratic formula that combines two spectral ratios of remote-sensing reflectance. For total absorption coefficients ranging from 0.02 to 2.0 m-• a goodness offit was achieved between the measured and modeled data with a root-mean-square difference between the measured and modeled values for log10 scale (RMSD•og•0) of0.062 (15.3% for linear scale, number of samples N = 63), while RMSDlog•0 is 0.111 (29.1% for linear scale, N = 126) for pigment absorption (ranging from 0.01 to 1.0 m-l). As alternatives to pigment concentration algorithms, the absorption algorithms developed can be applied to the coastal zone color scanner and sea-viewing wide-field-of-view sensor data to derive inherent optical properties of the ocean. For the same data sets, we also directly related the chlorophyll a concentrations to the spectral ratios and obtained an RMSDlog•0 value of 0.218 (65.2% for linear scale, N = 120) for concentrations ranging from 0.06 to 50.0 mg m -3. These results indicate that it is more accurate to estimate the absorption coefficients than the pigment concentrations from remotely sensed data. This is likely due to the fact that for the broad range of waters studied the pigment-specific absorption coefficient a 440 nm ranged from 0.02 to 0.2 m 2 (mg chl) -•. As an indirect test of the algorithms developed, the chlorophyll a concentration algorithm is applied to an independent global data set and an RMSDlog•0 of 0.191 (55.2% for linear scale, N 919) is obtained. There is no independent global absorption data set available as yet to test the absorption algorithms.