Observing the Earth with Polarisation – Aerosol Events Captured by 3MI

Last Updated

18 May 2026

Published on

08 May 2026

Introduction

The 3MI (Multi-viewing, Multi-channel, Multi-polarisation Imager) instrument was launched on 12^th August 2025 onboard the EPS-SG/A satellite. Since then, it has been continuously observing the Earth with its unique capability to measure polarised light reflected by the Earth-Atmosphere system.

Polarisation is a property of light in which the electric field oscillates in a specific direction, known as the plane of polarization. It is generated when sunlight interacts with atmosphere particles such as aerosols, ice crystals, and droplets. By measuring the polarised signal, 3MI enables advanced characterisation of aerosol properties supporting improvements in air quality forecasting, numerical weather prediction, early warning systems, and climate monitoring.

This gallery, created by the 3MI experts at EUMETSAT within the Remote Sensing and Products (RSP) Division, presents a selection of remarkable aerosol events captured by 3MI. In the classical RBG images (left), land, clouds, and aerosol structures are readily identifiable. In contrast, the polarized RGB images (right) reveal some additional features that are highly valuable for aerosol retrieval. For example, surface contribution is generally reduced (except for sun glint over water surfaces), while clouds usually appear grey or dark - except for liquid clouds observed under specific geometries, where rainbow-like features (cloud-bow) can be seen. Interestingly, aerosols are often highly visible, as they generate a significant polarized signal under many conditions.

The images shown here are based on a preliminary version of the 3MI Level-1 products. RGB composites are typically constructed using spectral bands 670 nm, 555 nm, and 443 nm.

Enjoy exploring these unique views of our atmosphere!

This first daily composite illustrates the ability of 3MI to provide quasi-global observations of the Earth-Atmosphere system on a daily basis. The standard natural-colour composite is overlaid with a polarisation-derived composite for one of the 14 viewing angles provided by 3MI, highlighting the additional and distinctive information revealed by polarisation.

Combined Aerosol Types in India and China

On 19 October 2025, 3MI observed, during the same overpass, the Indo-Gangetic Plain, the Tibetan plateau, and the Xinjiang province. In the first image, a very significant aerosol load is visible over the Gangetic plain. In the polarised image, the surface mostly disappears (e.g. over the Tibetan plateau, middle) and the aerosol plume covering a large part of the Gangetic plain is clearly captured (bottom). In contrast, the Xinjiang province (top) appears to exhibit limited aerosol presence under this viewing geometry.
The second image, the Xinjiang province is observed a few minutes earlier during the same overpass. Under this viewing geometry, which is very different from the first image, a significant aerosol background becomes evident, extending across the entire province. It extends up to about 2,000 m in altitude and is bordered by high mountains. This region is known for its very turbid atmosphere, dominated by natural dust and, particularly in winter, mixed with anthropogenic dust and urban/industrial pollutants.

This comparison highlights the importance of multi-angle observations, alongside spectral and polarimetric measurements, for improved aerosol detection and monitoring.

Wildfires in Patagonia (Chile)

In the early phase, the fire is active around the El Hayo region (middle of the image for 7 January 2026). The emitted smoke, visible in polarization with a reddish colour, is transported northwards and eastwards, following different wind corridors, and mixes with clouds when reaching the Atlantic Ocean. A smoke column is also transported westwards over the Pacific Ocean.
On 18^th January 2026, the fire is very active in Concepcion. A substantial column of smoke rises into the atmosphere and is transported north-westwards over the Pacific Ocean. In polarization, the smoke plume reveals its complexity and evolution as it travels further from the source.
On 26^th January 2026, the fire, still located in western Chile, is transported eastwards and rises into the atmosphere, where it becomes embedded within a cloud structure over the South Atlantic Ocean. Again, polarization clearly highlights the evolution of the plume properties, as well as its vertical development in the atmosphere.

Fine dust in the Bodélé Depression (Chad)

The Bodélé depression is known as a major source of fine dust transported across the Atlantic Ocean and an important source of nutrient minerals for the Amazon rainforest. On 14 November 2025, two significant aerosol sources, containing fine particles that generate polarisation, are visible: dust originating from the Bodélé region and smoke from biomass burning transported from the south-west.
The dominant north-easterly wind, which intensifies when passing between Tibesti and Ennedi mountains, exhibits a pronounced diurnal cycle. This strong wind lifts dust from the surface, with maximum intensity occurring in mid-morning, coinciding with the 3MI overpass. The image captured on 10 January 2026 clearly shows dust emitted the same morning (right), while a plume emitted the previous day remains visible 800 km away (bottom).
A similar, very frequent situation – occurring on about 100 days per year - is observed on 23 February 2026.

Wildfires and Biomass Burnings in South Africa & Amazonia

On 30^th October 2025, smoke – primarily generated by biomass burning in Zambia and Mozambique - reached Lake Malawi. This smoke, dominated by fine particles, produces a strong and clearly visible polarized signal.
On New Year’s Day (1 January 2026), smoke from biomass burning in Central Africa is visible in the bottom-right of the image. A distinct column of smoke, likely originating from plantations in the central Chad desert, is also captured with polarization (upper-right).
On 18^th January 2026, Central Africa shows intense biomass burning activity. Polarization highlights numerous small fires, the individual smoke plumes they generate, and their merging into a widespread smokey atmosphere.
A spectacular “comet-like” plume is observed on 28^th February 2026. This smoke plume, originating from a fire in the Amazon rainforest, has a very localised source in the State of Roraima, suggesting a link to deforestation activities.

Aerosol Events in Indo-Gangetic Plain (India)

This impressive collection of images, covering 12 days, from 31^st October to 11^th November 2025, illustrates the evolution of atmospheric conditions over the Indo-Gangetic Plain. Major aerosol sources are clearly visible, extending from New Delhi to Calcutta. The aerosols, characterized by a strong polarized signature, represent a mixture of smoke from cropland fires and anthropogenic pollution.

Desert dust wall from Algeria to Canary Islands

On 30^th March 2026, 3MI captured the 1,500 km-long wall of desert dust, emitted only a few hours earlier and extending across Algeria from north-east to south-west.
On the following day, 31^st March 2026, a particularly dense part of the dust plume reached the Canary Islands. The desert dust, clearly visible in the standard RGB composite, is also captured in polarization, providing additional information on particle microphysics. In the left part of the image, a spectacular cloud bow - a rainbow-like feature formed above liquid clouds – displays colorful iridescence influenced by the droplet size distribution of the liquid droplets at the top of the cloud. A pronounced backscattering peak is also observed in the upper-left.
On 1^st April 2026, the impressive desert dust plume continues to move eastwards over the Atlantic Ocean. A cloud bow remains visible in the upper-left of the image.