Evaluation of empirical and semi-analytical chlorophyll algorithms in the Ligurian and North Tyrrhenian Seas

Abstract

Abstract. The estimation of chlorophyll concentration in marine waters is fundamental for a number of scientific and practical purposes. Standard ocean color algorithms applicable to moderate resolution imaging spectroradiometer (MODIS) imagery, such as OC3M and MedOC3, are known to overestimate chlorophyll concentration ([CHL]) in Mediterranean oligotrophic waters. The performances of these algorithms are currently evaluated together with two relatively new algorithms, OC5 and SAM_LT, which make use of more of the spectral information of MODIS data. This evaluation exercise has been carried out using in situ data collected in the North Tyrrhenian and Ligurian Seas during three recent oceanographic campaigns. The four algorithms perform differently in Case 1 and Case 2 waters defined following global and local classification criteria. In particular, the mentioned [CHL] overestimation of OC3M and MedOC3 is not evident for typical Case 1 waters; this overestimation is instead significant in intermediate and Case 2 waters. OC5 and SAM_LT are less sensitive to this problem, and are generally more accurate in Case 2 waters. These results are finally interpreted and discussed in light of a possible operational utilization of the [CHL] estimation methods.

Plastic Debris Occurrence, Convergence Areas and Fin Whales Feeding Ground in the Mediterranean Marine Protected Area Pelagos Sanctuary: A Modeling Approach

“…As for SST, the CMEMS sea surface temperature nominal operational product for the Mediterranean Sea, daily gap-free maps (L4) at 1 km horizontal resolution (Buongiorno Nardelli et al, 2013) were chosen. Chl-a concentrations were estimated by the OC5 algorithm (Gohin et al, 2002) on NASA MODIS AQUA reflectances, 1 km space resolution, as this algorithm presents intrinsic robustness in the waters of the Ligurian and North Tyrrhenian Seas (Lapucci et al, 2012; more details in Supplementary Material).…”

Small-scale variability of the current in the Strait of Bonifacio

“…The OC5 algorithm, provided by Ifremer (Gohin et al 2002), was initially developed to give accurate [CHL] estimations on the Bay of Biscay and the English Channel oceanic and coastal areas. OC5, recently updated by data from the French Mediterranean area, presents intrinsic robustness for both oceanic and coastal waters when compared with other regional and global algorithms used in the Ligurian and North Tyrrhenian sea (Lapucci et al 2012) and also in other seas such as the Bay of Bengal (India) (Tilstone et al 2011). All the MODIS AQUA Level-2 files, containing all or part of the study area in July, August, and September 2012, were acquired from the online OBPG Data Processing System.…”

Parameterization of Spectral Particulate and Phytoplankton Absorption Coefficients in Sognefjord and Trondheimsfjord, Two Contrasting Norwegian Fjord Ecosystems

“…At 443 nm, where a p (λ) and a phy (λ) absorb maximum, least squares fit provided the following relationships in Sognefjord (Equations (9) and (10)) and Trondheimsfjord (Equations (13) and (14)). Following the second approach i.e., including the inner Sognefjord stations the relationships were derived as in Equations (11) and (12…”

“…This necessitates in situ observations and local, region-specific parameterizations of bio-optical algorithms for accurate retrievals of biogeochemical parameters [9,10]. Satellite retrievals of biogeochemical parameters via semi-analytical algorithms involving absorption and scattering coefficients have resulted in better estimates [11,12]. Absorption coefficients of phytoplankton have been proved more efficient in estimating ocean primary production than chlorophyll-a concentration (Chla) [13].…”