https://w3id.org/sciencelive/np/RAFOMMXsXiYG-lWxSyjomq6wkhjx4t_BLo01u7Buuif2s
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sub:assertion {
sub:sentinel2-parameter-asymmetry-open-source-westerschelde a <https://w3id.org/sciencelive/o/terms/Research-Synthesis>;
dc:subject <http://www.wikidata.org/entity/Q133878>, <http://www.wikidata.org/entity/Q199687>,
<http://www.wikidata.org/entity/Q4302480>, <http://www.wikidata.org/entity/Q47053>,
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<http://schema.org/endDate> "2026-07-25"^^xsd:date;
<http://www.w3.org/2000/01/rdf-schema#label> "Open-source Sentinel-2 reproduces the parameter-dependent water-quality retrieval asymmetry in the Westerschelde";
<https://w3id.org/sciencelive/o/terms/hasConditionsDescription> """This synthesis holds within the following scope:
- Domain and site: a turbid, mesotidal, well-mixed temperate estuary — the Westerschelde
(Netherlands). It generalises to comparable optically complex Case-2 estuaries, not to
clear open-ocean (Case-1) water.
- Processing chain: the fully open-source Acolite atmospheric correction with the Gons
et al. (2005) red-edge algorithm for chlorophyll-a (aGS) and the Nechad et al. (2010)
algorithm for turbidity (aN783). This is NOT the paper's proprietary C2RCC chain
(cGS / cN783); the synthesis compares an open-source chain against the paper's
proprietary result and does not re-run C2RCC.
- Sensor and period: Sentinel-2 MSI (A/B/C era), imagery 2016–2026.
- Reference: coincident Rijkswaterstaat in situ observations at along-axis stations;
turbidity compared in linear space (FNU on both sides, no unit conversion),
chlorophyll-a compared in log10 space, matching the paper's treatment of each.
- Sample sizes: small — turbidity N = 11 match-ups, chlorophyll-a N = 33. The direction
of each verdict is robust; precise magnitudes carry wide uncertainty.
- Design: a Replication (different site, different period, open-source processor), not a
Reproduction — the Sado in situ data are not public.
- Out of scope: grid-sensitivity of the retrieval (a HEALPix / DGGS GRID4EARTH
representation of the corrected fields) is deferred to a separate follow-up chain that
will extend this one; the primary validation stays on the native Sentinel-2 grid.""";
<https://w3id.org/sciencelive/o/terms/hasLimitationsDescription> """1. Not a head-to-head processor test. The paper's headline numbers (cGS R² = 0.63,
cN783 R² = 0.84) are the proprietary C2RCC chain, which was never run here (C2RCC
exists only inside ESA SNAP and crashes in the container). The synthesis compares an
open-source chain against the paper's published proprietary result; it does not prove
the open-source chain equals C2RCC on the same imagery. In particular, the finding
that open-source Acolite matches C2RCC for turbidity is a single-site observation, not
a general claim that Acolite outperforms C2RCC everywhere.
2. Small samples. With N = 11 (turbidity) and N = 33 (chlorophyll-a), each R² carries a
wide confidence interval. The composed asymmetry is qualitatively robust across the
two limbs; the exact R² values should not be over-read.
3. Single estuary, single reference network. Both limbs were validated in one
Westerschelde record against one in situ provider. Whether the parameter-dependent
asymmetry holds in structurally different estuaries, or against other reference
networks, was not tested here.
4. Retrieval bias not corrected. The turbidity retrieval carries a slight positive bias
(+6.91 FNU) and the chlorophyll-a retrieval a positive bias with a negative slope;
these are reported, not corrected, and would matter for any quantitative use.
5. Grid representation untested. Any sensitivity of these verdicts to spatial
re-gridding (HEALPix / DGGS) is explicitly out of scope and deferred to a follow-up
chain.""";
<https://w3id.org/sciencelive/o/terms/hasRecommendationDescription> """1. Do not treat \"Sentinel-2 water-quality retrieval\" as a single capability. Validate
and report accuracy per parameter: a chain trustworthy for turbidity can be
simultaneously unreliable for chlorophyll-a in the same water.
2. For estuarine turbidity monitoring (e.g. Water Framework Directive reporting), a
fully open-source Acolite + Nechad chain is a viable, citable alternative to the
proprietary C2RCC processor — here it matched and slightly exceeded the proprietary
result in a different estuary.
3. For estuarine chlorophyll-a, treat MSI retrievals in turbid Case-2 water as
provisional. The paper's call for \"a more complete set of match-ups\" stands; collect
more coincident in situ pairs and validate locally before any operational use, and do
not assume a red-edge algorithm is tracking pigment rather than backscatter.
4. Prefer open-source, operationally reproducible processing chains for replication and
monitoring: they make the retrieval auditable end-to-end and, on the turbidity limb
here, cost nothing in accuracy.""";
<https://w3id.org/sciencelive/o/terms/hasSynthesisDescription> """Sent et al. (2021) reported that Sentinel-2 MSI retrieves estuarine water-quality
parameters with parameter-dependent accuracy — strong for turbidity, weak for
chlorophyll-a. This synthesis composes two independent replication limbs and finds
that the asymmetry itself is what replicates. In an independent, more turbid estuary
(the Westerschelde) and with a fully open-source atmospheric-correction chain
(Acolite), the two parameters behave exactly as the paper's asymmetry predicts, but
they land on opposite verdicts. The turbidity limb CONFIRMS the paper: the open-source
Acolite + Nechad (aN783) chain retrieves in situ turbidity in strong agreement,
R² = 0.92 with a near-unity slope (0.86), meeting and slightly exceeding the paper's
proprietary C2RCC + Nechad (cN783) result of R² = 0.84. The chlorophyll-a limb
QUALIFIES the paper's own caution: the open-source Acolite + Gons (aGS) chain achieves
no useful agreement with in situ chlorophyll-a, R² = 0.10 (log10 space), far below the
paper's selected C2RCC + Gons (cGS) result of R² = 0.63, deepening rather than
resolving the weakness the original authors flagged. The composed, replicated result
is therefore not a single accuracy number but a structural property: Sentinel-2
water-quality retrieval accuracy is parameter-dependent, and that dependence survives
both a change of estuary and the replacement of the proprietary processor by an
open-source one.""" .
}
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<https://orcid.org/0000-0002-1784-2920> <http://xmlns.com/foaf/0.1/name> "Anne Fouilloux" .
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