The aquatic science products from the Earth Observation sensors developed mainly for land applications require vicarious calibration coefficients to increase the performance of the sensor in the case of highly absorbing surface such as coastal water which could be outside the range of validity of the radiometric coefficients provided by the mission. Within BELHARMONY project (funded by BELSPO, 2018-2020) the gains retrieval for the MSI/S2, OLI/L8 and Proba-V data acquired over coastal environment is performed by using satellite data acquired over the AERONET-OC stations (Zibordi et al., 2009) when in-situ atmospheric and water products are available. All the in situ measurements considered for the simulation of the sensor signal satisfy the quality assurance criteria, which means that the AERONET products are at level 2.0. The sensor signal is simulated by using the 6SV radiative transfer model (Kotchenova et al., 2007; Vermote et al., 1997). In order to minimize the aerosol effect on the remotely sensed signal as reported in Bassani et al., 2015, only images with contemporary in-situ AERONET products with low aerosol loading represented by the aerosol optical thickness at 550nm are considered suitable for this study. Regarding the micro-physical properties of the aerosol the inverse AERONET products are often lacking at level 2.0, to overcome this condition the size distribution is assumed bi-modal dominated by fine or coarse aerosol mode depending on the Angstrom exponent, which is the AERONET direct product sensitive to the aerosol particle size. Furthermore, the AERONET-OC normalized water-leaving radiance is also input for simulation of sensor signal by modifying the source code of the 6SV model. A new method for the spectral interpolation of the water AERONET product was proposed by mixing a cubic spline and an analytic function to obtain a hyperspectral water-leaving reflectance over the entire VNIR (visible and near-infrared) domain starting with values at the AERONET channels. In order to achieve an accurate simulated signal, the specular reflection of the water surface is considered by introducing as input the speed and surface direction of the wind provided by AERONET station and the approximate value obtained by the online NMMB/BSC-Dust model, respectively. The dataset was screened for the wind speed following the results presented in Moore et al., 2000; the threshold is fixed to 5m/s to limit the increasing of the water-leaving reflectance due to the white-caps over the water surface. The last screening is represented by the conditions about the geometrical configuration of the acquisition and illumination reported in Pahlevan et al., 2014 to minimize the sun glint effect by restricting the relative azimuth and the solar zenith angle. The 6SV model was run for each selected images. The simulated TOA (top of atmosphere) radiance continuous within the discrete-spectral domain VNIR and sampled every 2.5nm has to be convolved to the spectral response function (SRF) of the sensor to obtain the simulated sensor signal (REF). Finally, the gain is calculated as the ratio of REF/MEAS, where MEAS stands for the observed signal. The removal of available data allows to the reliability and validity of the input data and the outcome of this study. To this aim, this study requires to work over a sufficient number of observations in order to reduce the uncertainty in the final gain retrieval. New data in the next months are expected to be available over the AERONET stations improving the quality of the retrieved gains. References: - Zibordi,G.; Melin, F.; Berthon, J.-F.; Holben, B.; Slutsker, I.; Giles, D., D'Alimonte, D.; Vandemark, D.; Feng, H.; Schuster, G.; Fabbri, B.E.; Kaitala, S.; Seppala, J.: AERONET-OC: a network for the validation of ocean color primary products, Journal of Atmospheric and Oceanic Technology, 26(8), 1634-1651, doi:10.1175/2009JTECHO654.1, 2009. - Vermote, E.F.; Tanré, D.; Deuzé.; Herman, M.; Morcrette, J.J.; Kotchenova, S.Y.: Second Simulation of a Satellite Signal in the Solar Spectrum-Vector (6SV). Available online: http://6s.ltdri.org (accessed on 23 August 2016) - Kotchenova, S. Y. and Vermote, E. F.: Validation of a vector version of the 6S radiative transfer code for atmospheric correction of satellite data. Part II. Homogeneous Lambertian and anisotropic surface, Appl. Optics, 46, 4455-4464,doi:10.1364/AO.46.004455, 2007. - Bassani, C.; Manzo, C.; Braga, F.; Bresciani, M.; Giardino, C.; and Alberotanza, L.: The impact of the microphysical properties of aerosol on the atmospheric correction of hyperspectral data in coastal waters, Atmos. Meas. Tech., 8, 1593-1604, doi:10.5194/amt-8-1593-2015, 2015. - Pahlevan, N., Lee, Z., Wei, J., Schaaf, C. B., Schott, J. R., Berk, A.: On-orbit radiometric characterization of OLI (Landsat-8) for applications in aquatic remote sensing, Remote Sensing of Environment, 154, 272-284, doi: 10.1016/j.rse.2014.08.001.
Gain retrieval for low radiance calibration over Aeronet-OC sites
Bassani Cristiana;
2019
Abstract
The aquatic science products from the Earth Observation sensors developed mainly for land applications require vicarious calibration coefficients to increase the performance of the sensor in the case of highly absorbing surface such as coastal water which could be outside the range of validity of the radiometric coefficients provided by the mission. Within BELHARMONY project (funded by BELSPO, 2018-2020) the gains retrieval for the MSI/S2, OLI/L8 and Proba-V data acquired over coastal environment is performed by using satellite data acquired over the AERONET-OC stations (Zibordi et al., 2009) when in-situ atmospheric and water products are available. All the in situ measurements considered for the simulation of the sensor signal satisfy the quality assurance criteria, which means that the AERONET products are at level 2.0. The sensor signal is simulated by using the 6SV radiative transfer model (Kotchenova et al., 2007; Vermote et al., 1997). In order to minimize the aerosol effect on the remotely sensed signal as reported in Bassani et al., 2015, only images with contemporary in-situ AERONET products with low aerosol loading represented by the aerosol optical thickness at 550nm are considered suitable for this study. Regarding the micro-physical properties of the aerosol the inverse AERONET products are often lacking at level 2.0, to overcome this condition the size distribution is assumed bi-modal dominated by fine or coarse aerosol mode depending on the Angstrom exponent, which is the AERONET direct product sensitive to the aerosol particle size. Furthermore, the AERONET-OC normalized water-leaving radiance is also input for simulation of sensor signal by modifying the source code of the 6SV model. A new method for the spectral interpolation of the water AERONET product was proposed by mixing a cubic spline and an analytic function to obtain a hyperspectral water-leaving reflectance over the entire VNIR (visible and near-infrared) domain starting with values at the AERONET channels. In order to achieve an accurate simulated signal, the specular reflection of the water surface is considered by introducing as input the speed and surface direction of the wind provided by AERONET station and the approximate value obtained by the online NMMB/BSC-Dust model, respectively. The dataset was screened for the wind speed following the results presented in Moore et al., 2000; the threshold is fixed to 5m/s to limit the increasing of the water-leaving reflectance due to the white-caps over the water surface. The last screening is represented by the conditions about the geometrical configuration of the acquisition and illumination reported in Pahlevan et al., 2014 to minimize the sun glint effect by restricting the relative azimuth and the solar zenith angle. The 6SV model was run for each selected images. The simulated TOA (top of atmosphere) radiance continuous within the discrete-spectral domain VNIR and sampled every 2.5nm has to be convolved to the spectral response function (SRF) of the sensor to obtain the simulated sensor signal (REF). Finally, the gain is calculated as the ratio of REF/MEAS, where MEAS stands for the observed signal. The removal of available data allows to the reliability and validity of the input data and the outcome of this study. To this aim, this study requires to work over a sufficient number of observations in order to reduce the uncertainty in the final gain retrieval. New data in the next months are expected to be available over the AERONET stations improving the quality of the retrieved gains. References: - Zibordi,G.; Melin, F.; Berthon, J.-F.; Holben, B.; Slutsker, I.; Giles, D., D'Alimonte, D.; Vandemark, D.; Feng, H.; Schuster, G.; Fabbri, B.E.; Kaitala, S.; Seppala, J.: AERONET-OC: a network for the validation of ocean color primary products, Journal of Atmospheric and Oceanic Technology, 26(8), 1634-1651, doi:10.1175/2009JTECHO654.1, 2009. - Vermote, E.F.; Tanré, D.; Deuzé.; Herman, M.; Morcrette, J.J.; Kotchenova, S.Y.: Second Simulation of a Satellite Signal in the Solar Spectrum-Vector (6SV). Available online: http://6s.ltdri.org (accessed on 23 August 2016) - Kotchenova, S. Y. and Vermote, E. F.: Validation of a vector version of the 6S radiative transfer code for atmospheric correction of satellite data. Part II. Homogeneous Lambertian and anisotropic surface, Appl. Optics, 46, 4455-4464,doi:10.1364/AO.46.004455, 2007. - Bassani, C.; Manzo, C.; Braga, F.; Bresciani, M.; Giardino, C.; and Alberotanza, L.: The impact of the microphysical properties of aerosol on the atmospheric correction of hyperspectral data in coastal waters, Atmos. Meas. Tech., 8, 1593-1604, doi:10.5194/amt-8-1593-2015, 2015. - Pahlevan, N., Lee, Z., Wei, J., Schaaf, C. B., Schott, J. R., Berk, A.: On-orbit radiometric characterization of OLI (Landsat-8) for applications in aquatic remote sensing, Remote Sensing of Environment, 154, 272-284, doi: 10.1016/j.rse.2014.08.001.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
