The Fundamental Data Record for Land Dynamics (FDR4LDYN) project aims to build a long-term, analysis-ready data record based on radar backscatter observations from a succession of European Earth observation missions.

It is completed as part of ESA’s Heritage Missions programme in collaboration with the Vienna University of Technology (TU Wien) and the Delft University of Technology (TU Delft). TU Wien's Wolfgang Wagner is the scientific lead for the project, with Sebastian Hahn, Roland Lindorfer, Clay Harrison, and Thomas Melzer contributing key developments. Susan Steele-Dunne and Paco Frantzen from TU Delft support the project particularly in the area of vegetation dynamics.

Since 1991, European satellites have collected one of the world’s longest and most consistent C-band scatterometry records. These missions include ESA’s European Remote Sensing satellites, which carried the ERS scatterometer (ESCAT) instruments, and the EUMETSAT-operated MetOp series, which hosts the advanced scatterometer (ASCAT) instruments.

The upcoming addition of MetOp-Second Generation satellites, equipped with the SCA scatterometers, will extend this record into the 2040s.

Within FDR4LDYN, experts are inter-calibrating data from the ESCAT and ASCAT instruments, as well as ensuring future integration with MetOp’s SCA sensors.

In this article, we speak with key members of the FDR4LDYN team to discover more about the project’s progress and milestones – including plans to create interactive Jupyter Notebooks for users to access, explore and experiment with FDR4LDYN data.

Raffaele Crapolicchio – ESA’s technical officer for FDR4LDYN

What are the latest updates on the FDR4LDYN project?

It’s been an exciting year for FDR4LDYN. I am pleased to share that the critical design review (CDR) was held in TU Wien from 7 to 9 May, and it was great success. We also launched a project website in the days prior to the Living Planet Symposium.

During the critical design review, we discussed the design of the algorithm to compute various backscattering parameters, including sigma nought at 40 degrees, slope and curvature, which are vital for monitoring land dynamics parameters, such as soil moisture or vegetation water content.

The azimuth correction, which is quite crucial for deriving soil moisture in arid areas, was also presented alongside the cross-calibration between ESCAT and ASCAT.

The first version of the database containing the backscattering parameters will be available in November this year and used to showcase applications for soil moisture and vegetation monitoring, surface water and flood dynamics.

What were your highlights from the critical design review?

One of the key highlights was the participation of our EUMETSAT colleagues, who expressed significant interest in this activity. The organisation typically does not handle research and development work directly, but FDR4LDYN activities can substantially contribute to evolution of a key EUMETSTAT product in the Hydrological Satellite Archive Facility (H-SAF) framework.

We also had extensive discussions on the calibration approach between ESCAT and ASCAT, based on different assumptions, such as Rainforest gamma nought versus a transponder. These conversations resulted in the decision to run a sensitivity study to better understand the impact of the different approaches.

In summary, we are on a promising path to provide consistent backscatter parameters for land studies spanning 35 years or more. Additionally, we observed some interesting evolutions of the backscatter parameters over Greenland; this could be an exciting topic to explore in future projects designed to extend the data record to sea ice.

Why is FDR4LDYN important for ESA’s Earth observation activities?

What we are working on is vital for several reasons, and I'd like to outline a few key points from the ESA perspective:

• Continuous research and development activities on Heritage data can bring substantial value to current and future operational missions. Heritage data also help to extend the time span of operational missions, enabling climate applications. With data from ESCAT, ASCAT and SCA, we are now aiming to produce a record spanning more than 40 years.
• Although ESA is not directly involved in the operation of the MetOp ASCAT instruments, it is eager to collaborate with EUMETSAT to build a robust data record for climate studies. The valuable participation of EUMETSAT at the CDR demonstrates this approach.
• ESA is also committed to supporting research institutes, such as teams at TU Wien and TU Delft, to complete projects that maximise the value of ESA Heritage Missions and other current and future satellites

Roland Lindorfer – FDR4LDYN project manager at TU Wien

How has FDR4LDYN resulted in new scientific insight?

A recurring theme within the project is the dual nature of technical challenges, which often lead to new scientific insights. For instance, the inter-calibration process between ESCAT and ASCAT revealed unexpected signal behaviour over the rainforest, prompting us to investigate potential geophysical origins more closely. Understanding these discrepancies could enhance our knowledge of C-band radar interactions with dense vegetation.

Another example would be the azimuthal correction parameters, which not only harmonise backscatter across viewing directions but also hold potential as a data product on their own. They could be used for a broad array of applications, such as tracking urban expansion, vegetation dynamics in changing climates, sand dune migration, or even icesheet studies.

How are you ensuring the availability of the data record to users?

To ensure the broad usability of the FDR4LDYN data record, we are building interactive Jupyter Notebooks. These notebooks will not only provide clear, practical examples and guides for accessing and analysing the data, but also offer an intuitive environment for users to experiment with their own analyses and quickly generate meaningful plots. This approach is designed to lower the barrier to data usage, making our datasets freely accessible to a wider community, including those without specialised technical backgrounds.

Susan Steele-Dunne – FDR4LDYN’s scientist at TU Delft

How is FDR4LDYN helping to overcome challenges?

During the critical design review, I highlighted a persistent challenge: distinguishing actual vegetation dynamics from short-term soil moisture fluctuations. FDR4LDYN provides a good platform for testing the new regularisation approach for slope and curvature, designed to better capture the precise timing of rainfall-driven spikes.

Thomas Melzer – FDR4LDYN scientist at TU Wien

How have novel scientific approaches been used in FDR4LDYN?

I am exploring a Bayesian update to the current kernel-based method, aiming for more adaptable and robust slope and curvature estimates. The synthetic ESCAT experiment, which uses ASCAT data to replicate the sparse temporal sampling of heritage missions, offers a valuable opportunity to validate these novel approaches by using filtered observations as realistic test data. This work also deepens our understanding of the technical limitations imposed by irregular observation intervals.

Wouter Dorigo – ESA CCI Soil Moisture science lead and potential FDR4LDYN user

How does FDR4LDYN benefit the Earth observation community?

Looking at FDR4LDYN from the user perspective, the project is an important step to ensure that scatterometer data remain a trusted input for diverse geophysical applications, directly supporting ongoing ESA activities, such as its Climate Change Initiative (CCI).

By building this continuity and reliability, FDR4LDYN gives the user community confidence that the long-term C-band record will remain accessible and consistent well into the future.