Estimation of upward radiances and reflectances at the surface of the sea from above-surface measurements

Abstract

Abstract. During four field days in the years 2009–2011, 22 series of measurement were collected in the Inner Oslofjord. The data consist of recordings of spectral sub-surface and above-surface nadir radiances, as well as spectral downward irradiance in air. The studied wavelengths are 351, 400 nm and the 10 former MERIS channels in the range 413–754 nm. The water-leaving radiance and the reflected radiance at the sea surface can be determined from the measured nadir radiances in water and air. A simpler and much faster method, which determines the radiance reflectance at the surface as well as the water-leaving and reflected radiances solely from the measurements of upward nadir radiance and downward irradiance in air, is presented. A comparison between the quantities determined by the two methods shows that the average relative deviations between their results are less than or equal to 15% for the reflected radiance, at the studied wavelengths. The average relative deviations of the water-leaving radiance at 560 nm is 24%. We consider this to be acceptable uncertainties for a first check of satellite products in coastal waters.