Using coupled radiative transfer simulations for developing atmospheric correction for hyperspectral ocean colour remote sensing in application to the EnMAP mission
The major goal of this project is to develop an efficient atmospheric correction over water (open, coastal and inland waters), with defined uncertainties. This shall be done by using currently available (mostly open ocean) hyperspectral top of atmosphere (TOA) reflectance (RTOA) data from SCIAMACHY, HYPERION, HICO and simulations by the coupled atmosphere-ocean radiative transfer model (RTM) SCIATRAN (see Rozanov et al. 2014, Rozanov et al. revised). With the simulated data, atmospheric absorbing and scattering effects on RTOA can be precisely located and accounted for in the correction scheme, as well as other effects as glint and due to the proximity to the coast (e.g. mixed land-water pixels, adjacency effect, bottom reflection). These simulations will also be used to develop a correction scheme (look-up-tables, LUT) for these effects, as well as for estimating water leaving reflectance (RRS) from RTOA data. Particularly the atmospheric correction scheme Polymer, which was developed by HYGEOS for MERIS (Steinmetz et al. 2011) shall be investigated for its application to hyperspectral data (see further details under preparatory work by the PI). The developed atmospheric correction scheme and retrieval of RRS will be used by the HZG project to develop advanced water colour products (e.g. chlorophyll-a concentration of phytoplankton functional types, gelbstoff absorption). The uncertainty will be derived from SCIATRAN simulations, intercomparison and validation with in situ RRS (mainly coastal and inland waters made available by HZG) and satellite RTOA from multispectral sensors (e.g. MERIS). The developed algorithms will be tested on HICO and SCIAMACHY data (downscaled to ENMAP spectral resolution but keeping the spatial resolution) before ENMAP operation. After verification, the atmospheric correction scheme, which allows the retrieval of RRS, will be implemented into the ENMAP box.
V.V. Rozanov, A. Rozanov, A. Kokhanovsky, J.P. Burrows, J. Quant. Spectrosc. Rad. Transfer, 133, 13-71,(2014)
V.V. Rozanov, T. Dinter, A.V. Rozanov, A. Wolanin, A. Bracher, Burrows J.P. J. Quant. Spectrosc. Rad. Transfer, revised version submitted 30 Jan 2016.
F. Steinmetz, P.-Y. Deschamps, D. Ramon, Optics Express, 19(10), 9783–9800, 2011.