Published on 28 June 2022
Torrid eddies off the Balearic Islands
“I have just finished a collaboration on the vast eddies that form in the Mediterranean – in the Balearic Sea,” she explains. “Satellite data has allowed us to study two of these recent events, which occurred over a particularly long time. They lasted between two and four months.
By isolating certain water masses, these phenomena have an impact on both oceanic general circulation and ecosystems. The findings of this study reveal that these eddies have also led to an increase in temperature of around 2.5 degrees. “Considering the ocean as a whole, we could almost refer to these eddies as heat waves,” explains the oceanologist.
Remote identification of an eddy and temperature anomaly off the Balearic Islands detected by Sentinel-3
© Dr Alvera-Azcárate
An early spring in the North Sea
Closer to home, the early arrival of spring has been detected in the North Sea. Another study, which is part of the STEREO programme financed by Belspo, the Belgian Federal Science Policy, has enabled the researcher to identify another effect of global warming.
Based on more than twenty years’ worth of data related to chlorophyll in the sea, the oceanologist was able to prove that spring blooms are occurring increasingly earlier in the year. “There’s a difference of about one month between 1998 and 2020”, she explains.
The ULiège scientist owes these research findings to the use of satellite data. She regularly makes use of data from the European satellites Sentinel 3 and Sentinel 6, which are managed by EUMETSAT within the framework of the European Copernicus programme.
“Sentinel 3 is equipped with a series of instruments that provide data on our oceans’ altimetry, colours, chlorophyll content and the quantity of sediments, as well as temperatures,” explains Dr Alvera-Azcárate. “Sentinel 6, which goes by the name of Michael Freilich, has taken over the provision of altimetry data, which first began with the Jason satellites. And the data it delivers is extremely precise."
The instruments and data need constant fine-tuning
Although the instruments in space gather vast amounts of data, the data delivered needs to correspond as closely as possible to scientists’ needs. This is one reason why Aida Alvera-Azcárate is also concerned with how to improve the quality of satellite data. “One example of this is trying to eliminate specific disturbances, such as the shadows on the sea caused by clouds. These can cause the data provided by the satellites to be misinterpreted,” she explains.
This is a very tricky problem to solve because it is often difficult to tell cloud shadows and non-shaded areas apart. Shadows caused by clouds have similar spectral characteristics to water pixels.
In Brussels, Professor Véronique Dehant from the Royal Observatory of Belgium highlights another challenge related to improving spatial instruments: their localisation accuracy. “When we talk about the rise in sea levels, we are talking about altimetry,” explains the head of the Observatory’s Reference Systems and Planetology directorate.