https://w3id.org/sciencelive/np/RALzO6a4kKOJYXVS-9pEY48i-PDe25x4eBlzTBjGh7n9Y
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sub:langhovde-basal-lead-time-2022-outcome a <https://w3id.org/sciencelive/o/terms/FORRT-Replication-Outcome>;
<http://schema.org/endDate> "2026-10-09"^^xsd:date;
<http://www.w3.org/2000/01/rdf-schema#label> "Basal pressure vs acceleration onsets at Langhovde Glacier, January 2022: inconclusive (one event)";
<https://w3id.org/sciencelive/o/terms/hasConclusionDescription> """This record cannot tell whether basal water pressure rises before grounded-ice acceleration. The claim is therefore neither supported nor contradicted.
What is clear:
- In the one instrumented event (2–6 January 2022), rain and melt came first: rain began at 01:50 UTC on 2 January, and the basal pressure rise followed about 19 h later in every processing.
What is not clear:
- The order of pressure and acceleration depends on the processing.
- Centred smoothing of the published 15 min GNSS puts the speed rise about 8 h before the pressure rise.
- The same smoothing of the reprocessed 1 s GNSS puts pressure about 6 h before speed.
- Every past-only (causal) estimate is indeterminate, with spreads of more than ±10 h.
Why sharper data did not resolve it:
- The grounded and floating trunk stations share a ~12 h variability in speed that is larger than the event's speed-up. It is mostly not GNSS multipath and not a simple tidal response.
- The borehole tilt sensor was still settling.
The proposed held-out comparison of three nested models needs several events. In a single-event hold-out, adding basal pressure and uplift did not improve on weather and speed history.""";
<https://w3id.org/sciencelive/o/terms/hasConfidenceLevel> <https://w3id.org/sciencelive/o/terms/LowConfidence>;
<https://w3id.org/sciencelive/o/terms/hasEvidenceDescription> """Basal pressure and forcing:
- BH2201 basal water level peaked at 51.0 m a.s.l. (97% of flotation) at 23:07 UTC on 3 January 2022; 50.95 m after the measured air-pressure correction.
- Rain led the pressure rise by a median of 18.6–18.9 h (causal) and 20.8–23.4 h (centred), in 30–32 of 32 rule × bandwidth × reference combinations.
Pressure to GNSS1 (grounded) speed, onset leads (positive = pressure first):
- 15 min deposit:
- centred median −8.0 h (\"level lags\", 20 of 30 combinations);
- robust causal median +0.6 h, 13 earlier and 13 later (\"indeterminate\").
- 1 s kinematic GNSS (100% fixed; 5.7 mm and 3.7 mm horizontal SD against the published 15 min positions):
- centred median +5.75 h (\"level leads\", 16 of 32 combinations defined);
- robust causal, corrected for detection delay, median +3.6 h, range −7.6 to +36.1 h, 13 of 32 defined (\"indeterminate\");
- after sidereal filtering and tidal correction, still \"indeterminate\" (median +4.9 to +6.8 h).
- Detection delay of the causal speed estimators on synthetic onsets: 3.0–8.9 h (15 min data); 3.4 h (1 s data, h = 3 h).
Sub-daily variability at GNSS1:
- 12–13 h period, SD 0.047 m/d at h = 1 h, against an event speed-up of about 0.03 m/d (12.5%).
- Sidereal filtering removed 14% (GNSS1) and 32% (GNSS2) of the 10–15 h variance.
- A tidal model fitted before the event explained R² = 0.001 and 0.07 afterwards.
- GNSS1 and GNSS2 band-passed (6–18 h) residuals correlate at r = 0.97 (east), 0.72 (north) and 0.84 (up). GNSS1 and receiver LG1 correlate at 0.17, 0.23 and 0.00.
Bed tilt and nested models:
- Bed tilt in BH2201 drifted about 0.9 mrad/h, with 13 steps above 5 mrad (largest 77 mrad).
- Nested models, one-event hold-out at GNSS1 (h = 3 h): skill of the pressure-and-uplift model relative to weather-and-speed was −0.24, −0.05 and −0.01 at 1, 3 and 6 h horizons.
- Rolling-origin forecasts began only after the event onset.""";
<https://w3id.org/sciencelive/o/terms/hasLimitationsDescription> """- One event, at one site, in one season. No conclusion about lead time in general, or at other glaciers, can be drawn.
- The proposed predictive test was not run. The lead labels describe this event only.
- Basal pressure comes from one borehole, about 190 m from the grounded GNSS station.
- Onset times depend on the smoothing and the onset rule. All combinations are reported, not a chosen one.
- The origin of the ~12 h speed variability is not established: real trunk motion is likely, but differential troposphere cannot be excluded. What the two extra GNSS receivers stand on is not documented in the archive.
- The bed-tilt sensor was settling (drift and steps), so its onsets were withdrawn. The tilt-rate change during the pressure rise and the stick-slip-like steps after the peak are post hoc observations, not tested.
- Several steps were amended after results were seen (dated in ANALYSIS_PLAN.md).""";
<https://w3id.org/sciencelive/o/terms/hasOutcomeRepository> <https://doi.org/10.5281/zenodo.23266427>;
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<https://orcid.org/0000-0002-1784-2920> <http://xmlns.com/foaf/0.1/name> "Anne Fouilloux" .
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