Abstract:
Estuarine and coastal waters are characterised by highly variable and optically complex
conditions resulting from spatially and temporally heterogeneous distributions of optically ac
tive constituents (OACs), notably phytoplankton pigments, total suspended matter (TSM), and
chromophoric dissolved organic matter (CDOM). These aquatic environments, generally clas
sified as Case II waters, challenge conventional remote sensing methodologies due to the non
linear and spectrally overlapping contributions of absorption and scattering processes governed
by these constituents. This thesis presents a comprehensive investigation of the bio-optical
dynamics of estuarine and coastal ecosystems through an integrative approach combining
multi-seasonal in-situ radiometric, spectrophotometric, and remote sensing observations with
satellite-derived ocean colour products. The research specifically emphasizes the quantification
and remote sensing of CDOM and its implications for radiative transfer processes and coastal
ecosystem functioning. A semi-analytical retrieval algorithm was developed for the robust esti
mation of CDOM absorption at 440 nm (a440
CDOM) across diverse optical regimes by isolating the
CDOMsignal influencing the spectral reflectance and minimising the attenuation by the other
OACs. Thedevelopedalgorithmwasoftheform, a440
the three wavelength index given as x = ( 1
R412
rs
cdom = −0.01368x2+0.102x+0.02295, with
− 1
) ×R560
R490
rs
rs . This algorithm was formulated
and validated using an extensive global dataset of in-situ measurements comprising absorption
and attenuation coefficients, water-leaving radiance, and CDOM spectral slopes, acquired from
estuarine and nearshore coastal zones. Comparative evaluation against widely adopted empiri
cal and semi-analytical algorithms demonstrated superior performance of the proposed model,
yielding the highest coefficient of determination (r2 = 0.64) and the lowest error metrics (rmse
= 0.1039, mae = 0.064, mape = 51.96%). Notably, its accuracy improved under conditions
where CDOM exerted a dominant influence on the total absorption budget. The validation
using satellite-derived data from MODIS-Aqua and Sentinel-3 OLCI further substantiated the
algorithm’s applicability across a spectrum of Case II waters
