Helsinki ice update Feb. 25th

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.

Executive Summary

This update follows optical wetness and surface SAR analysis on February 20th with key optical band observations of:

• A major fracturing of the Melkki-Rysäkari corridor

• Increased activity on the Porkkala-Helsinki shipping lane

• Blominmäki waste water treatment outflow wetness area has widened

Sufficient SAR imagery was not available for this update.

Context since last update

Conditions favour fracturing conditions around ice edges due to:

• Temperatures: Between -2 to -10 degrees (FMI/Harmaja)

• Wind regime: Up to 14m/s gusts South and East

• Snowfall: ~10cm of new snow

• Reported events: None

New and existing snow cover weakens ice in areas influenced by currents (narrows, straits, outflows). This cannot be directly inferred from current satellite imagery.

Latest imagery

How to read False Colour (Sentinel-1)

False colour is based on optical bands and closely resembles what the naked eye would see:

• Dark blue to cyan returns —> Water

• White return —> Snow

• Red returns —> Vegetation

View fullsize

View fullsize

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

View fullsize

View fullsize

Feature 1 – Melkki-Rysäkari corridor

A distinct and broad fracturing and wetness is visible both false colour and NDWI, consistent with wet areas/very thin ice if not open water.

The feature is structurally connected to the main shipping corridor.

Interpretation confidence: High, based on clear optical return and NDWI signal.

Feature 2 – Porkkala-Helsinki shipping lane

The shipping lane return has strengthened, with also a clear new loop emerging north of Kytö.

The imagery indicates increased vessel activity.

Interpretation confidence: High, based on consistent optical and NDWI signal.

Feature 3 – Blominmäki waste water outflow pipe

The outflow location has increased in visibility in true colour imagery and NDWI (though remains small in the above images), with wet areas appearing around the open water area. The measured diameter of optical changes is appx. 350 meters.

The change indicates wetter/thinner ice surface around the open water.

Interpretation confidence: High, due to a well-known anomaly and clear optical and NDWI return.

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