Theoretical assessment of structure perturbations in above-water radiometry

A confident use of above-water radiometry requires that the perturbing effects of the deployment structure (structure perturbations, SPs) do not significantly affect the acquired data. A field experiment conducted at the Acqua Alta Oceanographic Tower (AAOT) in the north Adriatic Sea investigated SP dependence on the distance between the structure and the sensor footprint. Experimental results revealed clear SP patterns but also underlined the difficulty of a comprehensive analysis solely based on in situ measurements. On the theoretical side, several investigations examined how in situ radiometric data can be affected by the measurement setup, although they did not address the above-water case in full detail. The scope of this work is then to complement prior experimental and theoretical evaluations through a Monte Carlo analysis of SP in above-water radiometry. Results for the AAOT are presented in the context of the prior experimental findings and to support operational AERONET-OC measurements. In particular, the study shows that forward and backward Monte Carlo simulations provide complementary insights into the SPs dependence on factors such as spatial variability, measurement geometry and illumination conditions. On that basis, the work reports minimal SPs on AERONET-OC measurements at the AAOT when applying basic quality assurance criteria. These outcomes highlight how radiometric measurements taken with above-water systems deployed on fixed offshore structures and research vessels would benefit from theoretical SP analyses.