In situ determination of the remote sensing reflectance: an inter-comparison

Abstract

Inter-comparison of data products from simultaneous measurements performed with independent systems and methods is a viable approach to assess the consistency of data and additionally to investigate uncertainties. Within such a context the inter-comparison called <I>Assessment of In Situ Radiometric Capabilities for Coastal Water Remote Sensing Applications</I> (ARC) was carried out at the Acqua Alta Oceanographic Tower in the northern Adriatic Sea to explore the accuracy of in situ data products from various in- and above-water optical systems and methods. Measurements were performed under almost ideal conditions, including a stable deployment platform, clear sky, relatively low sun zenith angles and moderately low sea state. Additionally, all optical sensors involved in the experiment were inter-calibrated through absolute radiometric calibration performed with the same standards and methods. Inter-compared data products include spectral water-leaving radiance <I>L</I>_w (&lambda;), above-water downward irradiance <I>E</I>_d(0⁺,&lambda;) and remote sensing reflectance <I>R</I>_rs(&lambda;). Data products from the various measurement systems/methods were directly compared to those from a single reference system/method. Results for <I>R</I>_rs(&lambda;) indicate spectrally averaged values of relative differences comprised between −1 and +6%, while spectrally averaged values of absolute differences vary from approximately 6% for the above-water systems/methods to 9% for buoy-based systems/methods. The agreement between <I>R</I>_rs(&lambda;) spectral relative differences and estimates of combined uncertainties of the inter-compared systems/methods is noteworthy.