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|Title:||Validation of Satellite Ocean Color Primary Products at Optically Complex Coastal Sites: Northern Adriatic Sea, Northern Baltic Proper and Gulf of Finland|
|Authors:||ZIBORDI Giuseppe; BERTHON Jean-Francois; MELIN Frederic; D'ALIMONTE Davide; KAITALA Seppo|
|Citation:||REMOTE SENSING OF ENVIRONMENT vol. 113 p. 2574-2591|
|Publisher:||ELSEVIER SCIENCE INC|
|Type:||Articles in periodicals and books|
|Abstract:||The study presents and discusses the application of in situ data from the Ocean Color component of the Aerosol Robotic Network (AERONET-OC) to assess primary remote sensing products from Moderate Resolution Imaging Spectroradiometer (MODIS) and Sea-viewing Wide-Field-of-view Sensor (SeaWiFS). Three AERONET-OC European coastal sites exhibiting different atmospheric and marine optical properties were considered for the study: the Acqua Alta Oceanographic Tower (AAOT) in the northern Adriatic Sea exhibiting Case-1 and Case-2 moderately sediment dominated waters; and, the Gustaf Dalen Lighthouse Tower (GDLT) in the northern Baltic Proper and the Helsinki Lighthouse Tower (HLT) in the Gulf of Finland, both characterized by Case-2 highly yellow substance dominated waters. The analysis of MODIS derived normalized water-leaving radiance at 551 nm, LWN(551) has shown relatively good results for all sites with uncertainties of the order of 10% and biases ranging from -1 to -4%. Larger uncertainty and bias have been observed at 443 nm for the AAOT (i.e., 18 and -7%, respectively). At the same center-wavelength, results for GDLT and HLT have exhibited much larger uncertainties (i.e., 56 and 67%, respectively) and biases (i.e., 18 and 25%, respectively), which undermine the possibility of presently using remote sensing LWN data at the blue center-wavelengths for bio-optical investigations in the Baltic Sea. An evaluation of MODIS derived aerosol optical thickness, ¿a, has shown uncertainties and biases of the order of tens of percent increasing with wavelength at all sites. For AAOT, GDLT and HLT, ¿a(869) has shown an overestimate of 71, 101 and 91%, respectively. This result indicates the lack of an appropriate aerosol model for the atmospheric correction process, or the need of applying a vicarious calibration factor at the 869 nm center-wavelength to remove the effects of uncertainties in the atmospheric optical model and the space sensor radiometric calibration. Similar results have been obtained from the analysis of SeaWiFS data. Finally, in view of showing the possibility of reducing uncertainties and biases in satellite regional radiometric products, AERONET-OC data from the Baltic Sites (i.e., GDLT and HLT) have been applied to remove systematic errors introduced in MODIS LWN by the atmospheric correction process. Results have indicated a substantial reduction of uncertainty and bias in the blue and red center-wavelengths (e.g., decreasing from 60 and 21% to 20 and 5%, respectively, for LWN(443)).|
|JRC Institute:||Sustainable Resources|
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