Image of sea near the coastline

Coastal and Open Ocean Altimetry Data: How ALES unlocks insights from 1995 to today on EarthConsole®

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In the world of satellite altimetry, precision is key. For years, satellites have revolutionized how we measure sea levels, monitor ocean currents, and track environmental changes.

But there’s been one tricky area for researchers: coastal regions.

Historically, satellite altimeters have struggled to provide reliable data near coastlines.

That’s where ALES — the Adaptive Leading Edge Subwaveform retracker — available on EarthConsole® comes in, offering a new way to make accurate altimetry measurements.

What is ALES and why should you care?

ALES is a subwaveform retracking algorithm developed by Marcello Passaro from the German Geodetic Research Institute of the Technical University of Munich, to overcome the challenges altimeters face when measuring sea levels close to the coast.

ALES improves the accuracy of satellite data near coastlines, all while maintaining high accuracy in open ocean measurements, making it a relevant tool for scientists, oceanographers, and anyone tracking sea level rise or coastal changes.

How Does ALES Work?

To understand how ALES functions, let’s start with how satellite radar altimetry works.

Satellites send out radar signals that bounce off earth surface and catch the echoes as they bounce back. The time it takes for these signals to return helps calculate the distance to the surface, allowing us to determine for example sea level. While this process is straightforward in open waters, it becomes complicated near the coast due to interference from land or other reflective objects like for example ship traffic.

ALES works by looking at the signals the satellite gets back and focusing on a specific part of each signal – the leading edge. From this section, ALES makes a rough estimate of how tall the waves are. This information is important because knowing the wave height helps improve the accuracy of the data.

Once ALES has the wave height estimate, it can choose the best part of the wave signal to analyze. By narrowing its focus, ALES can avoid interference from other factors, such as reflections from land or ships. This targeted analysis helps to eliminate noise and enhances the quality of the data, resulting in more precise measurements of sea level.

ALES on EarthConsole®

You can now access an extensive time series of altimetry data spanning from 1995 to today, thanks to the addition of the bulk processing option for ALES for Envisat and ERS-2 data (both missions no longer operational in space) via the Heritage Missions Virtual Lab on EarthConsole®.

This addition complements the existing ALES+ SAR service for Sentinel-3 and CryoSat-2, which was already available for both bulk and on-demand processing via the Altimetry Virtual Lab on EarthConsole®.

This will provide you with a clearer understanding of how coastal zones and open ocean conditions have evolved over the last three decades.

Getting started with ALES for ENVISAT or ALES for ERS-2 (FREE ACCESS):

  1. Log in to www.earthconsole.eu.
  2. Request a free membership to the Heritage Missions Virtual Lab www.earthconsole.eu/groups/heritage-missions.
  3. Click on the card ‘Request the service you need’ and submit the service request using the dedicated form within the Lab.
  4. Wait for approval; it may take a few days as we process your request with ESA.
  5. Once approved, you’ll receive 100 free processing hours, which can be renewed for another 100 hours pending ESA approval.

What makes ALES stand out is its adaptability and versatility.

Whether it’s applied to older satellite missions like ERS-2 and Envisat, or the latest missions like CryoSat-2 and Sentinel-3, ALES is applicable to waveforms from different altimeters. This flexibility enables to extend the time series and ensures that we can analyze both historical and current satellite data to better understand sea level changes over time.

If you’re interested in finding out whether ALES is suitable for your research, feel free to contact us at info@earthconsole.eu.

OCRE Project by CENTEC: more than a decade of processed CryoSat-2 and Sentinel-3 AB data over coastal zones available on ESA Altimetry Virtual Lab

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We are pleased to share the conclusion of the European Commission OCRE (Open Clouds for Research Environments) [1] financed project led by CENTEC (Centre for Marine Technology and Ocean Engineering) – Instituto Superior Técnico de Lisboa. With our support here at EarthConsole®, this project aimed at evaluating renewable wave energy resources in the coastal zone, employing advanced high-resolution altimetry products.

CENTEC selected EarthConsole® among the providers of the OCRE Earth Observation catalogue to process data over selected coastal zones and an extensive period of 11 years (from January 2011 to December 2022) for CryoSat-2 data and 7 years (from April 2016 to December 2022) for Sentinel-3 data. The processing was conducted using the ESA-ESRIN SARvatore services for CryoSat-2 and Sentinel-3, which allow users to customise the processing from L1a to L2 data products, and include a list a configurable options such as the one used for this project, the enhanced geophysical retrieval algorithm known as the SAMOSA+ model and retracker.

These services are available for both systematic and on-demand processing via the ESA Altimetry Virtual Lab hosted on EarthConsole®.

The ESA Altimetry Virtual Lab is the virtual space that offers customised services to process Synthetic Aperture Radar Altimetry from CryoSat-2, Sentinel-3 and Sentinel-6 Michael Freilich missions, providing a community space for simplified services access and knowledge-sharing.

The areas of interest processed for this project are delineated in the accompanying figure below. Green areas represent processing with both CryoSat-2 and Sentinel-3 data, yellow areas are exclusively related to CryoSat-2 data, and blue areas represent processing with Sentinel-3 data.

To download the datasets, we invite you to log into the Altimery Virtual Lab and visit its datasets repository. A free of charge subscription to the Lab will be required in case you are not yet a Lab Member.

We remind you that you could also have the chance to get the costs of the ESA Altimetry Virtual Lab services covered, by requesting a voucher to the ESA Network of Resources.

[1] OCRE receives funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 824079

Picture including a measurement of the water level of a river.

EarthConsole® Stories: Monitoring water level changes in the Yangtze River using FF-SAR data

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EarthConsole® Stories are experiences about how we helped universities, research centres or service developers to leverage Earth Observation data to extract valuable insights for their research, educational or pre-commercial projects.

The Project

This study aims at using Sentinel-6 and Sentinel-3 FFSAR data for monitoring changes in water levels within the Yangtze River during the period of January 2019 to March 2023. A key objective of this study is to assess the precision of these datasets in the context of the Yangtze River, accomplished through comprehensive comparisons with both measured water level data and data sourced from alternative satellite monitoring systems.

In addition, the research extends into the topographical characteristics of the Yangtze River, involving a detailed analysis of waveform patterns and potential factors influencing transit points along the river. Furthermore, the study seeks to uncover the root causes behind the fluctuations in the Yangtze River’s water levels, achieving this by cross-referencing data with climate information.

The Need

The requirement at hand revolved around exploring the correlation between temporal and spatial changes in the Yangtze River’s water levels and climate change. Sentinel-3 and Sentinel-6 FFSAR data stood out for their renowned accuracy in monitoring river water level changes. To facilitate this investigation effectively, EarthConsole® offered the FFSAR (Fully Focused Synthetic Aperture Radar) processor for Sentinel-6 developed by Aresys, enabling to delve into this relationship.

Why EarthConsole®

In particular, the P-PRO (Parallel Processing) service within the ESA Altimetry Virtual Lab hosted on EarthConsole® has been selected to gain access to the FF-SAR processor to process Sentinel-6 L1a data on the Yangtze River Basin.

The EarthConsole® P-PRO service proved to be an ideal fit for our project, as it provided the reliable and readily available FF-SAR processor hosted on the platform. Furthermore, this service allowed us to entrust the processing management to EarthConsole® experts, allowing me to concentrate on my research and easily retrieve the results once they were ready.”

Shanmu Ma, Student at the Aerospace Information Research Institute, Chinese Academy of Sciences – China

This project has been supported via the ESA Network of Resources initiative.

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EarthConsole® Stories: Sentinel-6 potential of swell wave detection using FF-SAR data

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EarthConsole® Stories are experiences about how we helped universities, research centres or service developers to leverage earth observation data to extract valuable insights for their research, educational or pre-commercial projects.

The Project

In the context of the Space Flight MSc program at the faculty of Aerospace Engineering of the Delft University of Technology, this thesis project delved into the capabilities of the Sentinel-6 Michael Freilich satellite, the latest satellite altimetry mission, launched in November 2020 as part of the Copernicus programme.

The project aimed to compare two types of data, Level 1b Sentinel-6 Fully Focused Synthetic Aperture Radar (SAR) RAW and RMC data, to evaluate their differences in monitoring swell waves.

The project focused on the Channel Islands of California, where the presence of swells is dominant and especially evident in the winter period.

The Need

Recent research has shown that the performance of the RMC mode in unfocused SAR meets expectations. However, when it comes to fully focused SAR applications, there was still a need to evaluate the differences with RAW data.

That’s where EarthConsole® came into play. EarthConsole®’s Altimetry Virtual Lab provides the FF-SAR processor for Sentinel-6 developed by Aresys. This processor handles the entire journey of Sentinel-6 SAR data, starting from the raw FBR data and transforming it into FF-SAR Level1b products. This processor became indispensable since it provided FFSAR data required for extracting swell spectra information.

Why EarthConsole®

The research team chose to utilize the EarthConsole® P-PRO (parallel processing) service within the EarthConsole® Altimetry Virtual Lab to access the FFSAR (Fully Focused Synthetic Aperture Radar) for Sentinel-6.

In the course of the thesis project, creating an in-house FFSAR processor was simply beyond the project’s scope and the time constraints allocated for it. Consequently, we made the decision to leverage an external service, a choice that brought about several notable advantages. It afforded me access to a well-tested software solution and allowed me to fine-tune processing parameters to align with my specific requirements. Most notably, the substantial reduction in processing time, compared to running it on a local machine, emerged as a pivotal factor ensuring the project’s ultimate success.

The project impact

This performance analysis will be of great help to members of the scientific community who wish to use RAW data to analyze swells as it will highlight differences between RMC and RAW datasets thereby guiding a critical interpretation of the Sentinel-6 mission data.

 

This project has been supported via the ESA Network of Resources initiative.