Estimation of uncertainties in above-water radiometric measurements from hyperspectral and polarimetric imaging

Abstract

Uncertainties in radiance above the ocean surface are mostly determined by the skylight reflected from the air-water interface. Their accurate characterization is important for the accurate measurements of the water-leaving radiance as well as for the estimation of the impact of these uncertainties on the atmospheric correction of satellite and airborne ocean observations. Uncertainties are affected by the state of the ocean surface dependent on the wind speed and the corresponding reflection coefficient, which can be calculated based on Cox-Munk relationships. These uncertainties were estimated in the hyperspectral mode from shipborne measurements by the Hyperspectral Imager ULTRIS X20 (Cubert, Germany), with a 400-1000 nm wavelength range and a 410x410 pixel resolution. Measurements were taken during a VIIRS Cal/Val cruise in Hawaii area in a broad range of wind speeds 0-10 m/s and at viewing angles 20-60 degrees. In addition, airborne measurements from a helicopter at four different altitudes of 60, 150, 450, and 750 meters were carried out in different parts of Chesapeake Bay to establish a relationship between uncertainties and altitude. For these, a Teledyne DALSA M2450 polarized camera with a filter wheel containing several filters at different spectral bands was used together with the imager to characterize wave slope statistics and to determine uncertainties in measurements of the Stokes vector components and the degree of linear polarization (DoLP). Measurement uncertainties are further compared with simulations.