New outcomes from spatial remote sensing during the ECORS experiment : towards validation of ocean color products and large-scale bathymetry mapping in a coastal zone

DEHOUCK, A., MARTINY, N., FROIDEFOND, J.M., SENECHAL, N. and BUJAN, S., 2009. New outcomes from spatial remote sensing during the ECORS experiment : towards validation of ocean color products and large-scale bathymetry mapping in a coastal zone. Journal of Coastal Research, SI 56 (Proceedings of the 10th International Coastal Symposium), pg – pg. Lisbon, Portugal, ISBN High-resolution optical remote sensing is an important tool in beach morphodynamics studies. The sand bar systems on the beach can be covered at a few-meter resolution over several tens of kilometres alongshore. The remote sensing reflectance in the blue and the green wavelengths can be used to quantify the concentrations of the ocean constituents (SPM, CDOM, Chl-a) and estimate water depth. During the ECORS experiment, two FORMOSAT-2 scenes (2 and 8m of resolution), part of the Kalideos-Littoral database of CNES, were successfully acquired on February 10 2008 and April 5 2008. On April 5, a specific in-situ reflectance data set was collected onboard a jet-ski (3-25 m water depth), as well as water samples and bathymetric surveys. This unique synchronous data set represents a good opportunity : i) to validate high-resolution “ocean color” products in coastal shallow and turbid waters, ii) to calibrate an optical inversion algorithm for mapping bathymetry. Preliminary results are encouraging. The validation exercise is first focused on the remote sensing reflectance, used for bathymetry inversion. The match-ups between the remote sensing reflectance and the jet-ski measurements emphasize the importance of achieving previous accurate radiometric calibration of the spectral bands of the satellite and robust atmospheric corrections (under-estimate of the satellite-derived product by about 35-40% in the blue and the green using standard aerosol climatology). For the bathymetry inversion, the optical algorithm accurately reproduces the location and depth of the horns and troughs of the nearshore sandbar while it is less efficient seaward over the crest, overestimating water depth by 0.5-1.5 m.