Helsinki ice update Feb. 20th
Disclaimer: This is not safety advice or an advocacy to venture onto the ice. The writer is not professionally qualified to analyse ice conditions. Satellite interpretation reflects surface signals only and cannot determine load-bearing strength. Special safety precautions are required when travelling on ice.
Latest true colour image February 20th
Executive Summary
This update follows optical wetness analysis on February 17th. and surface SAR analysis on Feb. 15th with key observations of:
The dominant new feature is the Porkkala-Helsinki shipping lane, which now shows clear evidence of operational use
A north–south oriented lead has formed east of Koirasaari along the main shipping corridor
The previously fractured area around Koirasaari remains otherwise structurally static
Context since last update
Conditions favour surface refreezing due to:
Temperatures: Below -6 degrees (FMI/Harmaja)
Wind regime: 4-6m/s from North
Snowfall: No new snow
Reported events: Reported events: Blominmäki wastewater outflow area reported as covered with thin ice and snow
Existing snow cover may weaken ice in areas influenced by currents (narrows, straits, outflows). This cannot be directly inferred from current satellite imagery.
Latest imagery
How to read SAR (Sentinel-1)
SAR highlights structural features and surface roughness and penetrates non-packed snow cover.
Brighter returns —> rougher or fractured surfaces
Darker returns —> smoother surfaces or open water
SAR does not measure ice thickness or load-bearing strength.
How to read NDWI - Water Body Index
NDWI reflects surface moisture conditions.
Strong blue areas —> open water or very wet surfaces
Snow cover may mask moisture signals beneath
Cloud edges and shadowing can generate false positives; these are marked or commented where they affect interpretation
Note: Coast above Matinkylä, Lauttasaari Helsinki are under cloud cover
Feature 1 – Porkkala-Helsinki shipping lane
The shipping lane is visible for the first time in February in the NDWI wetness index and shows a continuous linear return in SAR.
The alignment and continuity strongly suggest recent vessel activity.
Interpretation confidence: High, based on consistent signal across both SAR and NDWI.
Feature 2 – Blominmäki waste water outflow pipe
The outflow location is visible in true colour imagery and faintly identifiable in SAR.
The feature is marked as a permanent weak location.
Interpretation confidence: High, due to a well-known anomaly
Feature 3 – Open lead near main shipping lane
A distinct north–south surface contrast has emerged east of Koirasaari.
The SAR signal indicates a smoother surface compared to the previous scene, consistent with either open water or recently formed thin ice.
The feature appears structurally connected to the main shipping corridor.
Interpretation confidence: High, based on clear surface differentiation since the previous image.
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