Ground truth measurements are necessary for the validation of remotely sensed data. Rapid ship or aircraft spectral measurements of the upwelling and downwelling (ir)radiance are needed to determine the reflectance of the water column as well, as to intercalibrate with satellite sensors. Intercalibrations are hindered by the application of different instruments with varying spectal bands. It is shown that when an optical data bank (ODB) of high resolution spectra (400-720 nm) of a specific sea area is available, it is possible to reconstruct new and old reflectance spectra, accurate to within 1 per cent almost over the full spectral range, out of the reflectance measured in five bands. The ODB could contain subsurface- or airborne-collected data. It appears to be possible to use simple instruments with five specific bands to compare with satellite data, even if these differ in central wavelengths. In this way high resolution spectral data could also be stored by means of only five bands. The reconstruction technique used is based upon a multiple regression analysis (MRA) or the OBD. To validate this full reflectance spectrum reconstruction method, spectral data collected with different radiometers in different locations were successfully regenerated from five key bands (412, 492, 556, 620, and 672nm). It is proposed that airborne spectral reflectance measurements could remain limited to only five specific spectral bands.