Remote sensing reflectance reconstruction to obtain water optical properties from MERIS multi-spectral satellite images Marjorie Schmeltz a , Jean-Marie Froidefond a , Frédéric Jourdin b and Peter Gege c a Université de Bordeaux 1, UMR 5805, avenue des facultés, 33405 Talence, France b Service Hydrographique et Océanographique de la Marine (SHOM), 29228 Brest, France c DLR Remote Sensing Technology Institute, Oberpfaffenhofen, D-82234 Wessling, Germany ABSTRACT We use a multiple regression analysis and a data bank of about 400 reflectance spectra to reconstruct hyperspectral reflectances between 400 and 900 nm with a 5 nm step using only the values known at the wavelengths of the MERIS sensor level 2 data. For in situ remote sensing reflectances measured during different oceanographic missions, the reconstruction is within 2 per cent almost over the entire spectrum. The main difference (to a maximum of 4 per cent) usually occurs at the inflexion point of the reflectance curve between 580 and 600 nm. Observed in-situ remote sensing reflectances or reconstructed spectra are inverted using a Water Colour Simulator bio-optical model (WASI) to obtain the inherent optical properties (IOP) of the water. The values derived by the model are compared with the measurements when available. To validate the reconstruction, we compare the results of the model inversion using the initial spectrum or the reconstructed one as input. Preliminary results show that the derived values from the inversion of the reconstructed spectrum are very close to the values generated from the inversion of the initial spectrum, especially in case 1 waters. This reconstruction technique is used to generate hyperspectral remote sensing reflectances from reflectance data calculated by the MERIS sensor. We use the reconstructed spectra as input to be inverted in the WASI model in order to quantify the substances' concentrations; in particular, the inversion is working well for the suspended particulate matter concentrations. Keywords: Coastal turbid waters; In-situ ocean colour measurements; WASI bio-optical model; Reflectance; Attenuation depth; CDOM. 1. INTRODUCTION About 400 hyperspectral Remote sensing reflectance (Rrs) spectra of the surface water were obtained with a TRIOS spectroradiometer mounted on a mini-catamaran [1] over different areas (Bay of Biscay, Mediterranean Sea, French Guiana shelf, off New Caledonia and Gabon coast). Simultaneously, hydrologic measurements (CTD, fluorescence, attenuation, scattering) and water samples were collected to measure suspended particulate matter (SPM), Chlorophyll-a and coloured dissolved organic matter (CDOM) concentrations. These optical measurements were carried out to determine the relationship between the water components and the remote sensing reflectance (Rrs). In the past, we have obtained several relationships between the suspended matter concentrations and the Rrs [2], [3]. But these relationships are empirical and with a low precision. Moreover, it was impossible to obtain CDOM and Chlorophyll-(Chla) concentrations in the case 2 waters. Consequently, the Water colour Simulator software (WASI, [4]) was selected to invert in-situ reflectance spectra. The satellite sensors MODIS and MERIS have multispectral channels and these data, although fit to be used as is in WASI, will only give multispectral inverted results and cannot be directly compared with our observed measurements. We use a multiple regression analysis and a data bank of over 400 reflectance spectra to reconstruct hyperspectral reflectances between 400 and 900 nm with a 5 nm step using only the values at the 15 wavelengths of the MERIS sensor (412.5, 442.5, 490, 510, 560, 620, 665, 681.25, 708.75, 753.75, 760.625, 778.75, 865, 885, 900). Then, these reconstructed spectra are used as inputs and inverted by WASI to obtain the Inherent Optical Proceedings of SPIE Vol. 7856 Remote Sensing and Modeling of the Atmosphere, Oceans, and Interactions III. SPIE Asia-Pacific Remote Sensing, Songdo Convensia Incheon, Republic of Korea, 11.-14. Oct. 2010