An algorithm to determine the spectral total absorption coefficient of water is presented. The algorithm is based on the Gershun’s equation of α = μKE. The spectral underwater average cosine, μ and vertical attenuation coefficient of net irradiance, KE were obtained from radiative transfer simulations using Hydrolight with large in-situ measured data from the coastal and estuarine waters of Goa. A refined algorithm of spectral μ as in Ref.  is used to determine the spectral underwater average cosine. The spectral KE was related to the diffuse attenuation coefficient, Kd. The algorithms to derive absorption were validated using an independent NOMAD optical data at wavelengths 412, 440, 488, 510, 532, 555, 650 and 676 nm. The performance of the algorithm was evident from the high R2, low bias and low RMSE. The values of R2 at wavelengths 412, 440, 488, 510, 532, 555, 650 and 676 nm were 0.95, 0.95, 0.93, 0.93, 0.88, 0.82, 0.62, and 0.65 respectively. The corresponding bias were -0.0064, 0.0076, 0.0038, 0.0044, 0.0122, 0.0124, 0.0362, and 0.0093 respectively. The algorithms for μ and KE provide the spectral weighted average within Z90 and have the advantage of deriving the absorption coefficients from the satellite data.