Improving the Atmospheric Correction of OLCI over Turbid Waters by Using
the SWIR band at 1016 nm and a new Baseline Residual Technique
Abstract
Since April 2016, the OLCI era has begun, providing a new opportunity
for atmospheric correction of turbid waters due to its novel spectral
band in the SWIR. This new band at 1016 nm, which is much less expensive
for the mission than longer SWIR bands (such as MODIS’ 1240, 1640 and
2130 nm bands) may give similar and even better performances than
far-SWIR and NIR bands for turbid water atmospheric correction with
suitable algorithm development. Although water absorption at this band
is 6.9 and 11.8 times higher than at 865 and 779 nm NIR bands, it is
still not enough to fully absorb the backscattered signal produced by
suspended sediments in very turbid waters such as Río de la Plata
(Argentina). This means that an alternative to the “black water”
approach is needed for this sensor in this region which makes special
use of the new SWIR band. In this work, we present an atmospheric
correction for turbid waters developed for OLCI, based on Baseline
Residuals (BLRs), i.e. spectral quantities computed from band triplets
(in the same way as the Fluorescence Line Height algorithm) of
Rayleigh-corrected reflectances in the Red/NIR/SWIR bands. The BLR
algorithm is evaluated and compared to results obtained with standard
atmospheric correction approaches, showing better general performance
and spatial de-correlation between atmospheric and water signal.
Although the algorithm has proven to yield satisfactory match ups of
Total Suspended Matter (Delgado et al. [Ocean Optics XXIV, (2018)]),
future efforts will be put in validating water reflectance using
radiometric field measurements.