[ARCHIVE] Mediterranean Sea Remote Sensing Reflectances and Attenuation Coefficient at 490nm from Multi Satellite and Sentinel-3 OLCI observations

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'''Short description:'''

The Global Ocean Satellite monitoring and marine ecosystem study group (GOS) of the Italian National Research Council (CNR), in Rome, distributes Remote Sensing Reflectances (Rrs), and diffuse attenuation coefficient of light at 490 nm (kd490) for multi-sensor (MODIS-AQUA, NOAA20-VIIRS, NPP-VIIRS, Sentinel3A-OLCI at 300m of resolution) (at 1 km resolution) and Sentinel3A-OLCI observations (at 300m resolution). Exclusively for multi-sensor also the absorption of phytoplankton (aph443), Gelbstoff material (adg443), and the particulate backscattering (bbp443) coefficients at 443 nm are provided. Rrs is defined as the ratio of upwelling radiance and downwelling irradiance at any wavelength (412, 443, 490, 555, and 670 nm for multi-sensor, and 400, 412, 443, 490, 510, 560, 620, 665, 674, 681 and 709 nm for OLCI) and can also be expressed as the ratio of normalized water leaving Radiance (nLw) and the extra-terrestrial solar irradiance (F0). Kd490 is defined as the diffuse attenuation coefficient of light at 490 nm, and is a measure of the turbidity of the water column. It is related to the presence of scattering particles via the ratio between Rrs at 490 and 555 nm (490 and 560 nm for OLCI). For multi-sensor observations Kd490 is achieved via Mediterranean regional algorithm developed by GOS on the basis of MedBiOp in situ dataset (Volpe et al., 2019). The current day data temporal consistency is evaluated as Quality Index (QI):

QI=(CurrentDataPixel-ClimatologyDataPixel)/STDDataPixel

where QI is the difference between current data and the relevant climatological field as a signed multiple of climatological standard deviations (STDDataPixel).

Inherent Optical Properties (aph443, adg443 and bbp443 at 443nm) are derived via QAAv6 model.

'''Processing information:'''

Multi-sensor products are constituted by MODIS-AQUA, NOAA20-VIIRS, NPP-VIIRS and Sentinel3A-OLCI. For consistency with NASA L2 dataset, BRDF correction was applied to Sentinel3A-OLCI prior to band shifting and multi sensor merging. Hence, the single sensor OLCI data set is also distributed after BRDF correction. Single sensor NASA Level-2 data are destriped and then all Level-2 data are remapped at 1 km spatial resolution (300m for Sentinel3A-OLCI) using cylindrical equirectangular projection. Afterwards, single sensor Rrs fields are band-shifted, over the SeaWiFS native bands (using the QAAv6 model, Lee et al., 2002) and merged with a technique aimed at smoothing the differences among different sensors. This technique is developed by The Global Ocean Satellite monitoring and marine ecosystem study group (GOS) of the Italian National Research Council (CNR, Rome). Then geophysical fields (i.e. chlorophyll, kd490, bbp, aph and adg) are estimated via state-of-the-art algorithms for better product quality.

'''Description of observation methods/instruments:'''

Ocean colour technique exploits the emerging electromagnetic radiation from the sea surface in different wavelengths. The spectral variability of this signal defines the so-called ocean colour which is affected by the presence of phytoplankton.

'''Quality / Accuracy / Calibration information:'''

A detailed description of the calibration and validation activities performed over this product can be found on the CMEMS web portal.

'''Suitability, Expected type of users / uses:'''

This product is meant for use for educational purposes and for the managing of the marine safety, marine resources, marine and coastal environment and for climate and seasonal studies.

'''Dataset names :'''

*dataset-oc-med-opt-multi-l3-rrs412_1km_daily-rt-v02

*dataset-oc-med-opt-multi-l3-rrs443_1km_daily-rt-v02

*dataset-oc-med-opt-multi-l3-rrs490_1km_daily-rt-v02

*dataset-oc-med-opt-multi-l3-rrs510_1km_daily-rt-v02

*dataset-oc-med-opt-multi-l3-rrs555_1km_daily-rt-v02

*dataset-oc-med-opt-multi-l3-rrs670_1km_daily-rt-v02

*dataset-oc-med-opt-multi-l3-kd490_1km_daily-rt-v02

*dataset-oc-med-opt-multi-l3-bbp443_1km_daily-rt-v02

*dataset-oc-med-opt-multi-l3-adg443_1km_daily-rt-v02

*dataset-oc-med-opt-multi-l3-aph443_1km_daily-rt-v02

*dataset-oc-med-opt-olci-l3-rrs400_300m_daily-rt-v02