Normalized Water-Leaving Radiance determined from above-water radiometry - Venise (45N,12E)

AERONET-OC “Acqua Alta Oceanographic Tower” (AAOT, also identified as Venise). The site established and maintained by the JRC since 2002 is located in the northern Adriatic Sea at approximately 8 nautical miles from the Venice Lagoon, and is characterized by optically complex waters moderately dominated by sediments. AERONET-OC is the Ocean Color component of the Aerosol Robotic Network (AERONET, Holben et al. 1998), a federated instrument network and data archive, managed by the Goddard Space Flight Center (GSFC) of the U.S. National Aeronautics and Space Administration (NASA) and specifically conceived to support aerosol investigations through standardized instruments and methods (Holben et al. 2001). Similar to AERONET, AERONET-OC (Zibordi et al. 2009) relies on NASA’s commitment for field instruments calibration, data processing and archiving. These activities are complemented by independent actions focused on establishing and maintaining CE-318 modified sun-photometers at coastal sites of interest for individual investigators or research institutions. These modified sun-photometers, called SeaWiFS Photometer Revision for Incident Surface Measurements (SeaPRISM), have the capability of performing autonomous above-water radiometric measurements in addition to usual atmospheric measurements (Zibordi et al. 2004). Key features of AERONET-OC are: i. near-real time data collection and processing (i.e., within a few hours); ii. use of standardized instruments, calibration procedure and data processing; iii. open access to measurements and products through a specified data policy. The primary data product of AERONET-OC is the Normalized Water-Leaving Radiance at wavelengths suitable for satellite ocean color applications. An additional product is the aerosol optical thickness, complemented by phase function, particle size distribution and single scattering albedo of aerosols, all having potential importance to assess the performance of the atmospheric correction process applied to satellite data. AERONET-OC sites are located in coastal regions by taking advantage of available and accessible offshore grounded structures. Deployment requirements for the collection of measurements suitable for ocean color validation activities are summarized as follows: i. fixed deployment platforms allowing for measurement of the direct sun irradiance through accurate sun-tracking; ii. superstructures with height and shape minimizing contamination of the measuring system by sea-spray; and iii. deployment positions allowing unobstructed sea observations at the maximum possible distance from the superstructure at the time of satellite overpass. Recalling that the minimization of superstructure perturbations in above-water radiometric measurements requires observations of the sea surface at distances at least equal to the superstructure height, the measurement systems are generally deployed from dedicated extensions of the main structure.