@prefix this: . @prefix sub: . @prefix np: . @prefix rdf: . @prefix prov: . @prefix npx: . @prefix dc: . @prefix xsd: . a np:Nanopublication; np:hasAssertion sub:assertion; np:hasProvenance sub:provenance; np:hasPublicationInfo sub:pubinfo; dc:created "2026-07-25T16:23:23.490Z"^^xsd:dateTime; dc:creator ; dc:license ; npx:introduces sub:chla-open-source-westerschelde-replication; npx:wasCreatedAt ; "Open-source Sentinel-2 chlorophyll-a retrieval validated against in situ data in the Westerschelde estuary"; . sub:chla-open-source-westerschelde-replication a , ; "Open-source Sentinel-2 chlorophyll-a retrieval validated against in situ data in the Westerschelde estuary"; , , , , ; """Five deliberate deviations, each recorded rather than hidden: 1. Atmospheric-correction processor. The paper selected C2RCC for its chlorophyll-a time series (the \"cGS\" chain, C2RCC + Gons). C2RCC exists only inside ESA SNAP and crashes natively in the container, so it is excluded; this replication runs Acolite instead, making the chain \"aGS\" (Acolite + Gons), an open-source analogue. Note the original study itself reports Acolite as its worst-performing processor. 2. Site. Validation is in the Westerschelde estuary, not the Sado, because the Sado in situ match-up data are available only on request (paper Data Availability Statement) and no open, contemporaneous, in-estuary substitute exists. The Westerschelde is a comparable mesotidal, well-mixed, turbid estuary. 3. Period. The record spans January 2016 to July 2026 (the full Sentinel-2 era), not the original's March 2018 to March 2020 field campaign, to gain the \"more complete set of match-ups\" the paper called for. 4. In situ reference. Coincident chlorophyll-a comes from Rijkswaterstaat routine monitoring stations, not the original AQUASado sampling campaign. 5. Fully open-source chain. Every step (Sentinel-2 L1C, Acolite, the Gons algorithm) is open and reproducible, whereas the original's selected chain depends on the proprietary SNAP/C2RCC processor."""; ; """The satellite half of the paper's pipeline is reproduced with a fully open-source chain (the \"aGS\" chain) and validated against an independent in situ reference. Sentinel-2 A/B/C Level-1C granules over the Westerschelde estuary are atmospherically corrected with Acolite to water-leaving reflectance, clipped to an estuary bounding box covering the along-axis stations. Chlorophyll-a is retrieved with the Gons et al. (2005) red-edge three-band algorithm, using the 665, 705 and 783 nm bands, transcribed from the original paper's Table 2; the bands are matched by nearest wavelength to absorb the Sentinel-2 A/B/C band-centre drift. At each in situ station a 3x3 pixel window is cut on the native 10 m UTM grid, with per-pixel quality control (water only, no cloud/shadow/glint, atmospheric-correction success), and the valid pixels are averaged. Satellite retrievals are paired with coincident in situ chlorophyll-a from Rijkswaterstaat monitoring stations on station and time within a plus-or-minus two-hour window. Agreement is scored with the paper's metric suite (coefficient of determination, slope, intercept, RMSE, bias, unbiased RMS, absolute and relative percentage difference), with the regression-family metrics computed in log10 space for chlorophyll-a and the percentage-difference metrics on untransformed values, exactly as the original specifies. Statistics are reported both over the full Sentinel-2 record and over the original study's field-campaign window, to separate the effect of changing the period from the effect of changing the site."""; """This study tests only the chlorophyll-a limb of the original claim: the assertion that Sentinel-2 MSI retrieval of chlorophyll-a is the weak side of a parameter- dependent accuracy — that chlorophyll-a is the parameter for which further research and a more complete set of match-ups are still needed. In scope is whether an independent, satellite-derived chlorophyll-a product agrees with coincident in situ chlorophyll-a measurements in a mesotidal, well-mixed, turbid estuary, and whether the original study's weak-chlorophyll-a caution still holds when the retrieval chain is fully open source and transferred to a different estuary and a longer period. Out of scope, and left to separate atomic chains, are the turbidity, suspended- particulate-matter and coloured-dissolved-organic-matter limbs of the paper's asymmetry, the seasonal time-series analysis, and any grid-sensitivity (HEALPix / DGGS) representation of the corrected fields."""; . sub:assertion prov:wasAttributedTo . 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