https://w3id.org/sciencelive/np/RAs--Uf0wMFAWeTv54c4P37QYNp70c8nxUY9M6HgOfg4c/Head https://w3id.org/sciencelive/np/RAs--Uf0wMFAWeTv54c4P37QYNp70c8nxUY9M6HgOfg4c http://www.nanopub.org/nschema#hasAssertion https://w3id.org/sciencelive/np/RAs--Uf0wMFAWeTv54c4P37QYNp70c8nxUY9M6HgOfg4c/assertion https://w3id.org/sciencelive/np/RAs--Uf0wMFAWeTv54c4P37QYNp70c8nxUY9M6HgOfg4c http://www.nanopub.org/nschema#hasProvenance https://w3id.org/sciencelive/np/RAs--Uf0wMFAWeTv54c4P37QYNp70c8nxUY9M6HgOfg4c/provenance https://w3id.org/sciencelive/np/RAs--Uf0wMFAWeTv54c4P37QYNp70c8nxUY9M6HgOfg4c http://www.nanopub.org/nschema#hasPublicationInfo https://w3id.org/sciencelive/np/RAs--Uf0wMFAWeTv54c4P37QYNp70c8nxUY9M6HgOfg4c/pubinfo https://w3id.org/sciencelive/np/RAs--Uf0wMFAWeTv54c4P37QYNp70c8nxUY9M6HgOfg4c http://www.w3.org/1999/02/22-rdf-syntax-ns#type http://www.nanopub.org/nschema#Nanopublication https://w3id.org/sciencelive/np/RAs--Uf0wMFAWeTv54c4P37QYNp70c8nxUY9M6HgOfg4c/assertion https://w3id.org/sciencelive/np/RAs--Uf0wMFAWeTv54c4P37QYNp70c8nxUY9M6HgOfg4c/wgs84-vs-sphere-sst-outcome http://schema.org/endDate 2026-04-22 https://w3id.org/sciencelive/np/RAs--Uf0wMFAWeTv54c4P37QYNp70c8nxUY9M6HgOfg4c/wgs84-vs-sphere-sst-outcome http://www.w3.org/1999/02/22-rdf-syntax-ns#type https://w3id.org/sciencelive/o/terms/FORRT-Replication-Outcome https://w3id.org/sciencelive/np/RAs--Uf0wMFAWeTv54c4P37QYNp70c8nxUY9M6HgOfg4c/wgs84-vs-sphere-sst-outcome http://www.w3.org/2000/01/rdf-schema#label WGS84 ellipsoid HEALPix geometry reduces FOSCAT SST gap-filling RMSE by 167.7 mK (12.6%) over sphere at operational resolution (nside=128) https://w3id.org/sciencelive/np/RAs--Uf0wMFAWeTv54c4P37QYNp70c8nxUY9M6HgOfg4c/wgs84-vs-sphere-sst-outcome https://w3id.org/sciencelive/o/terms/hasConclusionDescription The PCC research question is answered affirmatively at operational resolution: using WGS84 ellipsoid geometry instead of perfect-sphere HEALPix when resampling lat/lon SST observations to HEALPix cells reduces FOSCAT scattering-transform gap-filling RMSE by 167.7 mK (12.6%) at nside=128, on a single day of Copernicus Marine data. The geometry choice has a quantifiable effect on accuracy at the resolutions actually used in operational SST analysis pipelines, where 0.25° native data is binned into HEALPix cells comparable in size to the underlying observations. The benefit is resolution-dependent: at coarser resolution (nside=32), prior testing showed the WGS84 vs sphere difference collapses to ~1.5 mK (0.14%), well within run-to-run variability — i.e. at coarse resolution the geometry choice doesn't matter. The practical recommendation is to migrate to WGS84 geometry for operational SST gap-filling pipelines. https://w3id.org/sciencelive/np/RAs--Uf0wMFAWeTv54c4P37QYNp70c8nxUY9M6HgOfg4c/wgs84-vs-sphere-sst-outcome https://w3id.org/sciencelive/o/terms/hasConfidenceLevel https://w3id.org/sciencelive/o/terms/Moderate https://w3id.org/sciencelive/np/RAs--Uf0wMFAWeTv54c4P37QYNp70c8nxUY9M6HgOfg4c/wgs84-vs-sphere-sst-outcome https://w3id.org/sciencelive/o/terms/hasEvidenceDescription Single-day comparison on Copernicus Marine SST for 2026-04-01 at HEALPix nside=128 (12 × 128² = 196,608 total pixels). Inputs: L3S PMW (cmems_obs-sst_glo_phy_l3s_pmw_P1D-m) with cloud gaps, L4 analysis (cmems_obs-sst_glo_phy-temp_nrt_P1D-m) as gap-free reference. Pipeline parameters: NORIENT=4, KERNELSZ=3, lmax=60 (harmonic baseline), 300 L-BFGS iterations, CPU. RMSE measured against L4 in cloudy ocean pixels only. Sphere geometry: 134,587 ocean / 69,547 observed / 65,040 gap pixels — RMSE = 1333.0 mK, runtime 2081.8 s.\n\nWGS84 geometry: 134,472 ocean / 69,626 observed / 64,846 gap pixels — RMSE = 1165.3 mK, runtime 2083.2 s. Difference: WGS84 lower by 167.7 mK (12.6% relative reduction), with similar gap-pixel counts and identical runtime so the comparison is balanced. Full results JSON archived at Zenodo 10.5281/zenodo.19693573. https://w3id.org/sciencelive/np/RAs--Uf0wMFAWeTv54c4P37QYNp70c8nxUY9M6HgOfg4c/wgs84-vs-sphere-sst-outcome https://w3id.org/sciencelive/o/terms/hasLimitationsDescription Three caveats limit the strength of the conclusion. (1) Single-date evaluation. Only one day (2026-04-01) of L3S/L4 SST was tested at nside=128; cloud distribution, ocean regimes, and the gap pattern vary across days and seasons, so a multi-day study would strengthen the result. (2) L4 as ground truth. The 1333.0 / 1165.3 mK numbers are computed against the L4 operational analysis, not against in-situ measurements; L4 itself is an interpolation that may have its own systematic biases. (3) Single comparison resolution. This study's canonical run is at nside=128 only. 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