This study presents an empirical approach for estimating sea surface salinity (SSS) from remote sensing
of ocean colour. The analysis is based on two important empirical relationships of in-water optical
properties. The first involves the behaviour of the optical properties of coloured dissolved organic matter
(CDOM) under conservative mixing along the salinity gradient. The second is the tight relationship
between CDOM and water-leaving radiance. Our results showed that CDOM absorption coefficients
in ultra-violet wavelengths (350 and 380 nm) can be best estimated using the blue-green band ratio
Rrs(412/547) with a R2
value of 0.87. It was also found that the absorption coefficient of CDOM in
the study area was tightly correlated with the salinity (R2
≈0.83); however, the data indicate that this
relationship may be dependent on freshwater flow and the intensity of vertical mixing. During the wet
and well-mixed season (Northeast monsoon), CDOM was almost conservative with salinity but tended
to behave non-conservatively during the dry and stratified season (Southwest monsoon). These resulting
empirical relationships allow CDOM and salinity in the study area to be estimated from satellite ocean
colour data. Validation using independent datasets showed that the algorithms for CDOM and salinity
perform relatively well with the RMS error of 0.04 m-1 and 0.30`, respectively, over a range of salinity
from 30` to 33`. The ability of the algorithm to predict salinity as those presented in this study can be
further improved using more independent tests with in-situ and satellite bio-optical measurements.