Presentation slide about satellite altimetry research, featuring the title ‘ALES Evolves: Enhanced Output using FDR4ALT-Compatible Data for Altimetry Research.’ The slide includes a dark blue scientific design and an aerial view of a rocky coastline and turquoise sea, representing Earth observation, coastal monitoring, and remote sensing technologies.

ALES Evolves: Enhanced Output using FDR4ALT-Compatible Data for Altimetry Research

/in , , , , /by

We are pleased to announce a significant upgrade to the ALES (Adaptive Leading Edge Subwaveform) services for ENVISAT and ERS-2 missions. Developed by Marcello Passaro from the Deutsches Geodätisches Forschungsinstitut (DGFI) of the Technical University of Munich, this release brings an optimized output product designed to streamline research workflows.

This enhancement adds to a previous update that introduced compatibility with the ESA FDR4ALT (Fundamental Data Records for Altimetry) datasets. Together, these improvements provide a strong combined benefit for the scientific community working on altimetry projects.

What’s new

The focus of this release is the optimization of the ALES output product.

We know that managing large datasets can be a burden, so the new ALES version for ERS-2 and ENVISAT now integrates all relevant parameters from the input products directly into the final ALES output file1.

This means you no longer need to download or store bulky input datasets. Everything you need for your analysis is contained within the result file, making your data handling much lighter and faster.

Adding to existing FDR4ALT compatibility

This update leverages the previously introduced compatibility with FDR4ALT-generated datasets. The ESA FDR4ALT project was specifically designed to reprocess historical observations and bring them to a superior performance level for long-term time series.

This provides two main benefits for long-term oceanographic studies:

  • Enhanced Data Reliability: the combination of ALES retracking with FDR4ALT’s improved instrumental corrections ensures higher standards of data quality for coastal and open-ocean applications.
  • Multi-Decadal Continuity: this update facilitates the creation of high-quality time series spanning from 1995 (ERS-2) through 2012 (ENVISAT), which is essential for detecting climate trends and sea-level variations over decades.

The ALES Methodology: why it matters for Coastal Research

If you are new to the ALES processor2, it is important to understand why it has become widely used within the altimetry community.

Standard altimetry products often provide degraded performance as the satellite approaches the coastline. This is primarily due to land interference “polluting” the radar echo (waveform), which results in significant noise or data gaps.

ALES addresses these limitations through two specific innovations:

  • Subwaveform Retracking: unlike traditional retrackers that analyze the full radar echo, ALES focuses exclusively on the leading edge. By isolating a selected portion of the waveform containing the leading edge of the signal, the algorithm ignores the noisy “tail” caused by land interference or the glare caused by extremely calm water, retrieving valid sea-level measurements in areas where standard retrackers typically fail.
  • Adaptive Windowing: the algorithm dynamically adjusts its analysis window based on the significant wave height (SWH). This adaptive approach ensures high-precision measurements across varying sea states, maintaining consistency from the open ocean to within a few kilometers of the shoreline.

How to access the services for free

The ALES for ERS-2 and ENVISAT services are hosted within the ESA Heritage Missions Virtual Lab (HMVL) on EarthConsole®. The HMVL is an ESA initiative dedicated to the valorization of data from missions which are no longer operational in space.

You can choose the mode that best fits your workflow:

  • On-demand Processing: full control of your runs and its parameters through an intuitive Graphical User Interface (GUI).
  • Bulk Processing: let EarthConsole® operators handle large-scale data processing based on your specific requirements.

Access to the processing services is provided through the following steps:

Additional processing time (up to another 100 hours) can be requested subject to ESA approval. For large-scale processing requirements exceeding 200 hours, support may be available through the ESA Network of Resources (NoR) sponsorship.

For further clarification or support, please contact us info@earthconsole.eu. We would be happy to help.

1 It is important to note that in its current version, ALES for ENVISAT FDR4ALT does not implement a variable tracking gate as according to the section 6.2.8 of the FDR4ALT User Guide and therefore may show offsets in a small fraction of data for cycles 14,15 and 20.

2 References: Passaro, M., et al. (2014). ALES: A multi-mission adaptive subwaveform retracker for coastal altimetry. Remote Sensing of Environment. Read the paper here.