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Saint-Jean-sur-Richelieu, Canada

Santer R.,University of the Littoral Opal Coast | Zagolski F.,PARBLEU Technologies Inc | Aznay O.,C S Systemes dInformation
International Journal of Remote Sensing | Year: 2015

A good knowledge of the inherent optical properties (IOPs) of aerosols is a strong requirement for accurately performing atmospheric correction over the ocean. For several decades, IOPs have been computed using standard aerosol models (SAMs) that characterize the micro-physical properties of aerosols. These SAMs were used in the last generation of the Medium Resolution Imaging Spectrometer (MERIS) auxiliary data files (ADFs) to feed the atmospheric correction algorithm. Alternatively, Aerosol Robotic Network (AERONET) measurements can also provide IOPs. We built a database with the aerosol IOPs encountered over four AERONET stations in the North Sea plus one at the Acqua Alta Oceanographic Tower (AAOT, Venice, Italy). Several thousands of data sequences containing the aerosol IOPs were processed with filtering techniques and statistical methods to produce 16 classes of IOPs. An analysis of the dispersion of the IOPs within each class was conducted to evaluate the induced errors in the MERIS level-2 (L2) products in European coastal waters. We also investigated the reduction in the errors that can be achieved if there is access to auxiliary meteorological data (i.e. the relative humidity) or by using the bidirectionality in the satellite measurements, such as for advanced along-track scanning radiometer (AATSR) data. © 2015, © 2015 Taylor & Francis. Source

Aznay O.,ADRINORD | Santer R.,ADRINORD | Santer R.,University of the Littoral Opal Coast | Zagolski F.,PARBLEU Technologies Inc
International Journal of Remote Sensing | Year: 2014

A new approach has been developed to validate atmospheric correction (AC) over the ocean. The latter has been applied to the ground-segment data from the Medium Resolution Imaging Spectrometer (MERIS) on board the Environmental Satellite (Envisat) platform. An atmospheric validation database has been built up with a ground-based instrument, i.e. the Cimel radiometer from the Aerosol Robotic Network (AERONET). The aim of this work is to assess the atmospheric scattering functions needed to perform AC of remotely sensed data. The inputs to this new methodology were provided by AERONET, after inversion of radiometric measurements (i.e. solar direct extinctions and sky diffuse radiances) to get the inherent optical properties (IOPs) of the aerosols. The successive orders (SOs) of scattering code have been used as the radiative transfer tool in this study. This new concept for the validation of AC has been illustrated with the MERIS level-2 data extracted from the Meris Matchup In-situ Database (MERMAID) over the Acqua Alta Oceanographic Tower (AAOT, Venice - Italy). Results indicate first, an overestimate of the MERIS aerosol optical thickness (AOT) at 865 nm, and second, a marine reflectance affected by a negative bias of about 13% at 412.5 nm. This yields to an overestimate of the MERIS algal-1 pigment index, which may exceed 50%, over AAOT. The same trend is also observed in the determination of the algal-2 pigment index. © 2014 © 2014 Taylor & Francis. Source

Zagolski F.,PARBLEU Technologies Inc | Santer R.,ADRINORD | Santer R.,University of the Littoral Opal Coast
International Journal of Remote Sensing | Year: 2016

Performing a classical atmospheric correction over water requires a well-defined climatology representative of the aerosols encountered in the remote areas of oceans. Different climatologies built up at the global scale are candidates to be implemented, as an auxiliary data file (ADF) including look-up tables (LUTs) with radiative properties of the aerosols, in a traditional atmospheric correction algorithm. In addition to these, two regional climatologies were developed in the 2-Seas region, comprising both the Eastern English Channel and the North Sea, and at the Acqua Alta Oceanographic Tower (AAOT) in the Adriatic Sea. By using the optical data processor of the European Space Agency (ODESA), Medium Resolution Imaging Spectrometer (MERIS) level-1 (L1) data extracted from the MERis MAtchup In-situ Database (MERMAID) were processed to obtain the level-2 (L2) products over water. For a given climatology, a full processing chain was developed to generate the MERIS aerosol LUTs suitable to ODESA. The final step consisted of an analysis of the L2 products, for both the aerosols and marine reflectance, in the framework of the evaluation of the performance of each climatology in atmospheric correction over oceans. Finally, we recommend using the regional aerosol climatologies available from the AErosol RObotic NETwork (AERONET) database, at least for the retrieval of the L2 aerosol product. In regard to marine reflectance, this remains more challenging and needs a more extensive analysis. © 2016 Taylor & Francis. Source

Santer R.,University of the Littoral Opal Coast | Zagolski F.,PARBLEU Technologies Inc | Aznay O.,University of the Littoral Opal Coast
International Journal of Remote Sensing | Year: 2010

An approach to simulate the signal at the top of the atmosphere (TOA) in the visible and near-infrared regions is based on the exploitation of CIMEL sky radiances in three spectral bands (i.e. 440 nm, 675 nm and 870 nm). An iterative method, developed at the Laboratoire Interdisciplinaire des Sciences de l'Environnement (LISE, Wimereux, France), allows the aerosol phase function to be extracted from these ground-based measurements. Sky radiances are corrected for the multiple scattering based on the use of a radiative transfer tool and the aerosol phase function is derived from the primary scattering approximation. In order to cover the largest range of scattering angles, only the sky radiances acquired at low solar elevations are employed in this retrieval. These extreme geometrical conditions impose to adapt the radiative transfer code and to check its performances. Limits, performances and accuracy of this inverse method are discussed and illustrated both from the radiative transfer computations and from the CIMEL measurements. Moreover, thanks to the fact that the Aerosol Robotic Network (AERONET) also proposes CIMEL derived aerosol phase functions, the latter have been compared with our results. The substantial discrepancies that appear between the two sets are explained by the different objectives used in the two retrieval algorithms. © 2010 Taylor & Francis. Source

Aznay O.,University of the Littoral Opal Coast | Zagolski F.,PARBLEU Technologies Inc | Santer R.,University of the Littoral Opal Coast
International Journal of Remote Sensing | Year: 2011

The AErosol RObotic NETwork (AERONET) of CIMEL ground-based radio-meters, which covers the entire globe, has already been used in many previous studies for validating the inherent optical properties (IOPs) of aerosols. The IOPs are generally computed from microphysical properties using Mie's theory. Many recent studies link the uncertainties in these IOPs with the use of aerosol climatology based on microphysical properties. The objective of this study was to propose an alternative aerosol climatology based on the aerosol IOPs derived directly from CIMEL sky radiance measurements using our in-house iterative method. To achieve this task, an AERONET database of CIMEL sky radiance sequences was first processed using a specific set of criteria. Then, a representative subset of CIMEL data collected over the Venice site was used to refine the selected criteria and to evaluate new criteria for the data quality check, such as the preliminary tests applied to CIMEL sky radiances, the speed-up of convergence of our aerosol phase function retrieval algorithm, and the consistency of it soutputs. Because the extraction of the phase function requires a good knowledge of the surface reflectance, we used MODerate Imaging Spectroradiometer (MODIS) albedo maps, which are available on a monthly basis. Statistical methods were then applied to the CIMEL database to discard the incorrect sequences and to suggest a classification of the aerosol models on the basis of their IOPs. The need to include specific aerosol models in this climatology to account for Saharan duststorms, as well as to describe the Asian dust events, was also investigated in this study. Moreover, the medium-resolution imaging spectrometer (MERIS) look-up tables (LUTs) generated over land with these new aerosol IOPs are fully compatible with the currentlevel-2 algorithms.The improvement expected with this climatology will be evaluated using the MERIS imagery. © 2011 Taylor & Francis. Source

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