From calm breezes to destructive cyclones, winds shape Earth’s weather and climate. Satellites allow us to observe these dynamic patterns from above — revealing their structure, strength, and change.

Understanding Wind

Tropical storms are powerful weather systems capable of producing damaging winds, intense rainfall and storm surges. They are structured, low-pressure systems that develop over warm ocean waters of at least 27°C, with maximum sustained wind speeds ranging between 63 km/h and 118 km/h. Their formation and intensity directly relate to environmental conditions including sea surface temperature (SST), atmospheric pressure, wind patterns, and moisture content.

Once a storm has a wind speed greater than 118 km/h, it may be classified as a hurricane (North Atlantic and Northeast Pacific), cyclone (South Pacific and Indian Oceans) or typhoon (Northwest Pacific). These storms are categorised into intensity levels based on the Saffir-Simpson Hurricane Wind Scale.

Measurements of wind speeds are critical to categorising these storms and supporting disaster preparedness. While ground-based measurements provide critical, timely observations, space-based measurements can provide consistent, global coverage, as well as providing critical observations over the oceans where tropical storms often develop and intensify.

Measuring Wind from Space

Traditional methods for measuring wind from space include the use of radar scatterometers alongside optical imagers. Operational tropical storm forecasts and warnings are issued by national and regional meteorological agencies, who rely on a wide range of observations and models. Novel methods for understanding wind have been developed in recent decades, and include the use of radars, lidars and microwave imagers. Through its Earth Explorer and Third Party Missions, ESA provides complementary, science-quality satellite data that expand global coverage and deepen understanding of storm processes, feeding into the development of the broader forecasting system.

ESA’s Soil Moisture and Ocean Salinity (SMOS) mission carries the Microwave Imaging Radiometer using Aperture Synthesis (MIRAS) instrument, which images in the L-band at a frequency of 1.41 GHz. Since 2018, ESA has provided the SMOS Wind Data Service, which derives surface wind speed over the ocean from SMOS brightness temperature measurements - a parameter that takes into account sea surface salinity, temperature, and roughness. In very high winds, the SMOS L-band radiometer provides valuable information on the status of the ocean surface layer as its signal does not saturate, and is less sensitive to rain. As a result, SMOS wind data provides useful complementary observations to those from traditional sensors.

Three wind products are available from SMOS:

• SMOS Near Real Time Level 2 swath wind speed (SMOS L2WS NRT): SMOS retrieved surface wind speed gridded maps with a spatial sampling of 1/4° x 1/4°. These products are available within 4 to 6 hours from sensing.
• SMOS wind radii fixes (SMOS WRF): Contains the SMOS 10-minute maximum-sustained winds (in knots) and wind radii (in nautical miles) for the 34 kt (17 m/s), 50 kt (25 m/s), and 64 kt (33 m/s) winds per geographical storm quadrants and for each SMOS pass intercepting a tropical cyclone in all the active ocean basins. SMOS WRF products are available within 4 to 6 hours from sensing.
• SMOS Level 3 daily wind speed (SMOS L3WS): Daily composite maps of the collected SMOS L2 swath wind products for a specific day. Available the day after sensing.

C-band Synthetic Aperture Radar (SAR) data, such as that provided by Copernicus Sentinel-1 and RADARSAT, can also be used to derive wind speed for tropical storms. For example, Sentinel-1 Level-2 products provide gridded estimates of surface wind speed and direction (Ocean Wind Field) and two-dimensional ocean swell spectra that includes wind information (Ocean Swell Spectra). RADARSAT data can be accessed through ESA’s Third Party Missions Programme, and are available in the RADARSAT-1 and -2 Full Archive and Tasking catalog, as well as the ESA Archive of RADARSAT-2.

Furthermore, although ESA’s CryoSat satellite was designed to monitor polar ice, its radar altimeter — like those on other radar altimetry missions — also contributes to oceanographic and meteorological products, including wind data. By measuring the roughness of the sea surface, these instruments enable the derivation of wind speed estimates.

Together, these instruments provide a near-real-time view of winds at the ocean surface, forming the foundation for understanding and forecasting tropical storm behaviour.

Profiling the Structure of Storms

The Earth Cloud Aerosol and Radiation Explorer (EarthCARE), a joint mission by ESA and the Japanese Aerospace Exploration Agency (JAXA), is providing new insights into the vertical structure of tropical storms. Together its cloud profiling radar and multispectral imager reveal the height, composition, and layering of clouds within storm systems, adding to our understanding of the structure of storms.

ESA’s Aeolus mission was the first satellite mission to acquire profiles of Earth’s wind on a global scale, with its Doppler Wind Lidar, ALADIN. While the mission ended in July 2023, ESA continues to provide Aeolus data in its Phase F, which has the objective to improve the quality of the products and incorporate the latest algorithm evolution. The data are designed for the use in Numerical Weather Prediction (NWP) models and atmospheric scientific research.

Building on Aeolus, ESA has selected the Wind Velocity Radar Nephoscope (WIVERN) mission as the 11th Earth Explorer. WIVERN is designed to extend this capability into the heart of storm systems. Using a conically scanning Doppler radar, WIVERN will provide the first global observations of winds inside clouds. Paired with precipitation and cloud profiles, these observations would represent a breakthrough for understanding and modelling tropical storms.

Together, EarthCARE, Aeolus and WIVERN mark a shift from observing winds at the surface to mapping their full three-dimensional structure — from ocean to cloud top.

Exploring Wind Data from ESA

The LOPS (Laboratory for Ocean Physics and Satellite remote sensing) Data Visualization Portal provides global coverage of ocean surface wind speeds derived from multiple satellite missions. The platform collates wind speed data from a variety of radar satellites, including SMOS, Sentinel-1 and RADARSAT-2. This is supplemented by meteorological products from missions such as the MetOp series of satellites.

The Sentinel Application Platform (SNAP), developed for ESA by Brockmann Consult, Skywatch, Sensar, and C-S, is an architecture utilised by all Sentinel toolboxes. The individual SNAP toolboxes support a variety of sensors, including Sentinel-1, Sentinel-2 and SMOS, as well as Third Party Mission sensors. One of those toolboxes is SNAP Desktop, a user tool for data visualisation and analysis.

The CyclObs project, a joint collaboration between Ifremer and OceanScope and funded by ESA, EUMETSAT, CNES and ANR, is working on algorithms to retrieve geophysical parameters such as ocean surface wind speed and storm structure metrics using C-band SAR, and co-locating and comparing observations with those from L-band radiometers such as SMOS.

Using Wind Data: Hurricane Erin

Hurricane Erin was a large, long-lived, and powerful storm that crossed the North Atlantic Ocean in August 2025. The storm achieved peak intensity on 16 August, reaching 1-minute sustained wind speeds of up to 260 km/h near the Leeward Islands. The hurricane continued moving north along the east coast of the United States of America and Canada, significantly affecting Virginia, North Carolina, and Massachusetts in the USA, and Nova Scotia and Newfoundland in Canada.

As Sentinel-1 passed over the North Atlantic Ocean on 11 August 2025, SAR detected the first hurricane of the 2025 Atlantic hurricane season, Hurricane Erin. Between 11 and 17 August 2025, Sentinel-1 and RADARSAT-2 satellites captured an increase in Erin’s maximum sustained wind speeds (VMAX), with SATCON and ATCF estimates indicating intensification to Category 5 strength. SAR measurements confirmed these estimates. Hurricane Erin's VMAX values began gradually decreasing on 19 August, eventually dissolving near the coast of Newfoundland, Canada.

In addition, Hurricane Melissa, one of the strongest Atlantic hurricanes on record with top winds of 295 kilometres per hour, tracked across the Caribbean in late October 2025. As the storm passed by the Jamaican coast, SMOS captured two datasets showing the surface wind speed in the area.

These observations from SMOS, Sentinel-1 and RADARSAT-2 complement the traditional meteorological observations, and allow for better overall forecasting and understanding of the winds in tropical storms.

This understanding will be further expanded on with Europe’s plans to operationalise the Aeolus concept, with the EUMETSAT Polar System Aeolus (EPS-Aeolus) constellation. ESA will provide two satellites, to be launched sequentially, that will both carry a Doppler Wind Lidar instrument, following on from the success of Aeolus. In addition, the scientific understanding of winds will continue to expand with the upcoming development and launch of WIVERN, the 11th Earth Explorer.