Estimating the diffuse attenuation coefficient of the Photosynthetically Available Radiation (KPAR) allows to monitor primary production, dissolved organic matters, coastal suspended sediments and water transparency. The latter aim, especially for military purposes, may be efficiently achieved with the use of underwater gliders. The present study aims at estimating the KPAR in the the Bay of Biscay (North-East Atlantic), during a sea campaign which took place in February 2021, in fairly transparent waters mainly containing non-living suspended material. The sea survey involved a SEAEXPLORER glider equiped with an ocean color radiometer. The glider measurements were in agreement with those from shipboard CTD-PAR casts (with a mean relative difference of about 11%). VIIRS L2 and MODIS L4 satellite products were validated with the glider data. Accordingly, a bias correction has been proposed for the ocean color satellite KPAR algorithm.