Data from ESA’s SMOS mission are driving many space weather applications, ranging from air navigation, characterisation of solar flares, space weather modelling and ionospheric electron content mapping.

The Soil Moisture and Ocean Salinity (SMOS) mission is the first ESA Earth Explorer mission to provide microwave L-band measurements, thanks to its Microwave Imaging Radiometer using Aperture Synthesis (MIRAS) instrument. While the data are successfully used to observe global variability in soil moisture, sea surface salinity, sea ice thickness, sea surface wind speed and freeze/thaw soil state, more and more applications within the domain of space weather have emerged.

Practical demonstrations of space weather applications using these L-band measurements were showcased last year at the second workshop on SMOS for Space Weather, held in Alcalá de Henares, Madrid, Spain. The one-day workshop had 33 attendees in hybrid format, featuring eight presentations.

SMOS’s MIRAS is a passive microwave 2D interferometric radiometer (L-Band, 1.4 GHz, 21 cm) that captures signals emitted from Earth's surface, but also those coming from the Sun.

In this way the L-band signal contains hidden information about solar flux, that researchers have recently leveraged into good quality data products useful for space weather applications.

One of the highlights of the workshop was the presentation of a recently developed algorithm to obtain the solar flux at 1.4 GHz from MIRAS/SMOS data for space weather purposes.

The algorithm has been developed, verified and validated during an ESA-funded project coordinated by Deimos Romania. Solar flux at 1.4 GHz from MIRAS/SMOS data – when available in real time – will greatly enhance existing capabilities for air navigation.

At the workshop, the Space Weather Research Group of the Universidad de Alcalá presented their recent work within this ESA-funded project, on data validation and calibration of the upgraded SMOS solar flux prototype datasets to make them useful for space weather applications.

Useful applications in L-band radio systems

The team’s aim with data validation was to evaluate the performance of the prototype datasets under different solar and instrument scenarios. They showed the new algorithm had high sensitivity to weak solar signals and can detect intense radio bursts even when the Sun is far behind the antenna plane.

As SMOS L-band measurements can detect the circular polarisation of solar radio bursts, the data can help improve the correlation between the intensity of GNSS signal fades and the intensity of the solar radio bursts that produce them. This property is useful also for other problems in L-band radio systems, such as false echoes in some air control radars.

In terms of data calibration, the group showed that the internal calibration of SMOS is robust, meaning that discrepancies between the values measured by SMOS and those from reference observatories are in general not larger than discrepancies between the reference observatories themselves.

Solar flux dataset maps impact on satellite navigation

Also at the workshop, a solar flux prototype dataset was presented by Serco Red Lab, showing how the team developed an algorithm to estimate the solar flux from the information provided by operational Level-1 processor (v724), which removes the stray solar signal noise from L-band Earth measurements.

The algorithm derived the L-band Solar flux products by applying some geometrical corrections and calibrations, and results were validated using reference solar flux measurements from ground-based radio telescopes.

The team shared several practical applications of the solar flux dataset, such as evaluating the impact of space weather on GNSS. As the data have a long-time coverage, and can be produced with different temporal resolution, they are also useful for space weather modelling.

Since the dataset carries polarimetric information, they can be used to characterise Solar Radio Bursts (SRB), that can interfere with GNSS signals. SRBs are an indicator of the release of coronal mass ejections during solar flares. For example, during a major solar flare peaking at 17:02 GMT/16:02 CET on 14 December 2023, classified as X2.8, SMOS partially captured the associated SRB.

Airspace users need timely space weather information

As the Sun emits intense amounts of radiation and energy in its solar wind, it causes dynamic space weather that can impact air navigation in many ways. Solar radiation can affect onboard aircraft systems, and risk overexposure in crews and passengers.

Space weather can also cause loss of high-frequency satellite communications and cause degradation in timing and positioning of GNSS.

In Spain, the International Civil Aviation Organization (ICAO) space weather advisories are accessible to users in the ENAIRE ICARO application and the MET service provider application. Airspace users are responsible for consulting this information when planning their flight.

At the workshop, ENAIRE described user needs for space weather information from the perspective of the air navigation service provider, such as prediction times corresponding to timely notifications to airspace users for space weather events, particularly those longer in duration than 15 minutes.

The University of Alcalá invited ENAIRE to consider Local Disturbance Index as an indicator for the perturbation of the geomagnetic field, which is a parameter of interest to analyse potential impacts on GNSS.

Besides these applications, SMOS radiometric data support ionospheric research by allowing retrieval of Vertical Total Electron Content (VTEC) of the ionosphere. Monitoring the VTEC of the ionosphere is important for applications ranging from navigation to detection of space weather events.

A presentation by researchers at the Universitat Politecnica de Catalunya (UPC), in Barcelona, provided updates on the team’s work to derive global VTEC maps using SMOS data.

While the SMOS mission’s primary objectives are focused on investigating key scientific questions about Earth’s system, the SMOS for Space Weather workshop makes it apparent that there are many concrete space weather applications under development for SMOS observations.