TY - JOUR
T1 - Estimating underwater light attenuation from space – A spectral approach for case 2 marine waters
AU - Holbach, Andreas Michael
AU - Stæhr, Sanjina Upadhyay
AU - Stæhr, Peter A.
AU - Markager, Svend
PY - 2025/7/15
Y1 - 2025/7/15
N2 - Water clarity is a key indicator of marine ecosystem health, responding to eutrophication and influencing the distribution of phototrophic life on the seafloor. Traditional ship-based measurements of underwater light profiles and diffuse light attenuation coefficients (Kd) remain fundamental for environmental monitoring, including in Danish waters. However, satellite-based estimates of water clarity are often challenged by optically complex (case 2) waters and limited spectral coverage. This study presents a novel empirical spectral modelling approach across the range of photosynthetically active radiation (PAR) from 400 to 700 nm that • integrates existing individual spectral models of inherent optical properties (IOPs), • applies Sentinel-3 satellite-derived IOPs at 443 nm in this model, • employs a multivariate outlier removal procedure to enhance accuracy, and • estimates KdPAR through an iterative procedure mimicking the way it usually is determined in situ with PAR sensors. Model-derived KdPAR estimates were validated against in situ measurements from Danish marine waters (2018–2023) and compared with two simpler non-spectral satellite-based approaches. Results showed strong agreement between modelled and in situ KdPAR (n = 1458, R = 0.63), outperforming existing satellite-based methods. The new KdPAR product effectively captured spatial and temporal variability in complex case 2 waters, though discrepancies were noted in optically shallow areas, heterogeneous water columns, and seasonal phytoplankton shifts. These findings highlight the potential of operational satellite-derived IOP products as a robust proxy for water clarity, providing a valuable supplement to limited in situ data. The improved spatial and temporal coverage supports enhanced environmental monitoring, aligning with EU Water Framework and Marine Strategy Framework Directives.
AB - Water clarity is a key indicator of marine ecosystem health, responding to eutrophication and influencing the distribution of phototrophic life on the seafloor. Traditional ship-based measurements of underwater light profiles and diffuse light attenuation coefficients (Kd) remain fundamental for environmental monitoring, including in Danish waters. However, satellite-based estimates of water clarity are often challenged by optically complex (case 2) waters and limited spectral coverage. This study presents a novel empirical spectral modelling approach across the range of photosynthetically active radiation (PAR) from 400 to 700 nm that • integrates existing individual spectral models of inherent optical properties (IOPs), • applies Sentinel-3 satellite-derived IOPs at 443 nm in this model, • employs a multivariate outlier removal procedure to enhance accuracy, and • estimates KdPAR through an iterative procedure mimicking the way it usually is determined in situ with PAR sensors. Model-derived KdPAR estimates were validated against in situ measurements from Danish marine waters (2018–2023) and compared with two simpler non-spectral satellite-based approaches. Results showed strong agreement between modelled and in situ KdPAR (n = 1458, R = 0.63), outperforming existing satellite-based methods. The new KdPAR product effectively captured spatial and temporal variability in complex case 2 waters, though discrepancies were noted in optically shallow areas, heterogeneous water columns, and seasonal phytoplankton shifts. These findings highlight the potential of operational satellite-derived IOP products as a robust proxy for water clarity, providing a valuable supplement to limited in situ data. The improved spatial and temporal coverage supports enhanced environmental monitoring, aligning with EU Water Framework and Marine Strategy Framework Directives.
KW - Coastal waters
KW - Diffuse light attenuation coefficient
KW - Monitoring
KW - Ocean optics
KW - Sentinel-3
KW - Spectral model
KW - Water clarity
UR - http://www.scopus.com/inward/record.url?scp=105006833512&partnerID=8YFLogxK
U2 - 10.1016/j.scitotenv.2025.179775
DO - 10.1016/j.scitotenv.2025.179775
M3 - Journal article
C2 - 40450779
SN - 0048-9697
VL - 986
JO - Science of the Total Environment
JF - Science of the Total Environment
M1 - 179775
ER -