Radiometric field inter-comparison of fiducial reference measurements using an open source community processor

A radiometric field intercomparison was conducted at the Acqua Alta Oceanographic Tower (AAOT) in the Adriatic Sea from 14 to 21 July 2022 to assess differences in the accuracy of above-water radiometer systems (Sea-Bird HyperSAS, pySAS, TriOS-RAMSES) processed using an open-source community processor (HyperCP). Class-based and sensor-specific characteristics of the radiometers were used to determine the quantities <i>E</i>_<i>d</i>(<i>λ</i>), <i>L</i>_<i>sky</i>(<i>λ</i>), <i>L</i>_<i>t</i>(<i>λ</i>) and <i>R</i>_<i>rs</i>(<i>λ</i>), and their associated uncertainties. Using sensor-specific characteristics, the differences among systems were 2% for <i>E</i>_<i>d</i>(<i>λ</i>), <i>L</i>_<i>sky</i>(<i>λ</i>), <i>L</i>_<i>t</i>(<i>λ</i>) and 2.5% for <i>R</i>_<i>rs</i>(<i>λ</i>) and the uncertainties were 1.5%, 2%, 1.5% and 5%, respectively. The differences were higher when using class-based characteristics. <i>L</i>_<i>wn</i>(<i>λ</i>) values were also compared to the above-water AERONET-OC SeaPRiSM and in-water HyperPro II. For SeaPRiSM, the differences and uncertainties were <5% over blue and green bands when using Mobley [App. Opt.38, 7442 (1999)10.1364/AO.38.007442] sea surface reflectance factors (ρ) and no NIR correction. For HyperPro II the differences were larger but were reduced when <i>R</i>_<i>rs</i>(<i>λ</i>) from the above-water systems was computed using ρ from Zhang et al. [Opt. Express25, A1 (2017)10.1364/OE.25.0000A1] with similarity (sim) spectrum (spec) NIR correction. HyperCP using sensor-specific characteristics is highly recommended to reduce the associated uncertainties and to produce the highest quality data for satellite OC validation.