Ice sheets
Small icebergs add a lot of Greenland fjord freshwater
Open access · cc by · source: Europe PMC
High-resolution UNet mapping finds far more small icebergs than Sentinel-2 thresholding, raising Sermilik meltwater estimates toward ~2000 m³ s−1.
How this study connects
Role on claims
Each row is a claim on a concept or method page where this paper supports, challenges, or qualifies the statement. Roles are hand-checked — not a model guess.
A UNet trained on ~10,000 manual labels in ~3 m Planet imagery mapped 60.4 km² of icebergs in Sermilik — ~50% more area than same-day Sentinel-2 top-of-atmosphere thresholding, with ~5× more small bergs. Size distributions follow a power law only above ~300 m². Along-fjord discharge is ~1310 m³ s⁻¹ (~2020 m³ s⁻¹ in a June–July comparison). Small bergs, which optical thresholding undercounts, melt near the surface.
Evidence for the claim as stated.
Optical and radar ice products do not count the same objects at the same timescale. Planet UNet finds ~50% more iceberg area and ~5× more small bergs than Sentinel-2 thresholding; 12-day Sentinel-1 glacier speeds smear events that GNSS resolves daily; ITS_LIVE annual mosaics average many Landsat pairs. A student who adds Sermilik meltwater, Greenland lake-terminus speed, and Iceland spring speed-up as one ‘SAR velocity’ is mixing sensors, resolutions and averaging windows.
Evidence for the claim as stated.
Open questions
Tensions this paper is part of
From concept pages' “where studies disagree.” Disagreement means the same question; scope means different assays, populations, or outcomes.
Optical and radar ice products do not count the same objects at the same timescale. Planet UNet finds ~50% more iceberg area and ~5× more small bergs than Sentinel-2 thresholding; 12-day Sentinel-1 glacier speeds smear events that GNSS resolves daily; ITS_LIVE annual mosaics average many Landsat pairs. A student who adds Sermilik meltwater, Greenland lake-terminus speed, and Iceland spring speed-up as one ‘SAR velocity’ is mixing sensors, resolutions and averaging windows.
Discoveries this paper informs or conflicts with
- Remapping Greenland's bed doubled the count of glaciers warm water can reach
This paper informs this development.
Study at a glance
- Design
- Other — UNet mapping of icebergs in Planet imagery vs Sentinel-2 thresholding in Greenland fjords
- N
- N=10000 · ~10,000 manual iceberg labels used to train the UNet
- Population
- Icebergs in Sermilik and Kangerlussuaq fjords, East Greenland
- Outcome
- Higher small-iceberg area and meltwater discharge estimates (~1300–2000 m³ s−1 Sermilik)
Structured fields used in claim comparison tables when every cited study has a complete layer.
Inspect source passages
Small icebergs add a lot of Greenland fjord freshwater
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
Authors manually annotated 10,000 iceberg instances.
We manually annotate a total of 10,000 instances of icebergs in those sub-images and perform elastic deformation and random rotation to augment the training data to a total of 1800 sub-images (over 40,000 iceberg instances, see Section S2.2).
How many more small icebergs appear in Planet imagery?
However, the total number of small icebergs in Planet imagery is nearly five times greater than those in Sentinel-2 (Fig.
Key findings
P-UNet mapped 60.4 km² of icebergs in Sermilik, ~50% more than S-TOA, with ~5× more small bergs. Size distributions follow a power law only above ~300 m². Sermilik discharge is ~1310 m³ s−1 along-fjord and ~2020 m³ s−1 in a June–July comparison, exceeding some prior melt estimates; small bergs melt near the surface.
Methodology
Authors trained a UNet on ~10,000 manual iceberg labels in ~3 m Planet imagery of Sermilik and Kangerlussuaq fjords, compared with same-day Sentinel-2 TOA thresholding, fit size distributions, and converted area to meltwater with empirical keel/width relations.
Limitations
Two fjords and a few summer images do not give an annual cycle. Melt rates ignore fjord stratification and deep keels. Power-law extrapolation of small-berg contribution year-round is an assumption.
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