For about 30 years now, ESA satellites have been cruising some 800 km above our heads, collecting information about our planet—but why are older missions still so fundamental today?
ESA has been gathering Earth observation data for a long time: it started systematic acquisition and archiving of data from other agencies' satellites in the late 1970s – known today as 'Third Party Missions' – as part of the Earthnet Programme, while it launched its first European Remote Sensing satellite (ERS-1) in 1991 followed by ERS-2 in 1995 and Envisat in 2002.
The measurements that the Agency initiated with its own satellites in 1991, continue to be acquired today with evolved instruments on-board the Sentinel satellites of the European Union's Copernicus programme.
Today, there are many institutions, scientists and private companies that still rely on data from heritage (historical) missions for their work. These data are merged and compared with data from active missions, to ensure reliable measurements for the services they offer, or for scientific studies, requiring comparison of today's situation with that of the past.
One example is the Italian company Survey Lab, in Rome. They develop applications in many fields of civil and environmental engineering, with a focus on methods for monitoring natural hazard effects on land and the environment, over long time periods.
Survey Lab was founded as a spin-off company in 2008, by professors and researchers of the Department of the Civil, Environmental and Construction Engineering Faculty at the Sapienza University of Rome. They created an EU H2020 technology transfer project called I.MODI (Implemented Monitoring System for Structural Displacement), based on open data from ESA's archive. They started with ERS and Envisat data and then began to use the Copernicus Sentinels as their data became available.
DInSAR (Differential SAR Interferometry) time series constitute the base of Survey Lab's service. Open data access from ESA's archive (ERS and Envisat) are fully integrated to sustain long-term analysis that now rely on Copernicus Sentinel data and other on-going SAR missions.
In particular, data from the Copernicus Sentinel-1 and Sentinel-2 missions provide high-resolution radar and optical data on a global scale—fundamental for such monitoring.
Current satellite missions collect data with high frequency, with some able to systematically revisit the same location in the same geometry every 6 days. Past missions allow for an historical analysis, using archived data that cover the entire Earth from 1991 to the present.
I.MODI exploits Earth observation data to develop customised services for monitoring the stability of buildings in large urban areas and assessing critical civil infrastructures (for instance, roads and dams).
It integrates satellite measurements and in situ information within numeric models in order to quantify damage to structures and infrastructure, allowing anyone to utilise the outcome of a DInSAR analysis, even if they do not have a scientific background.
"The I.MODI service is a tool that prevents future failures and performs rearward analysis to better understand the causes of instability processes," states Maria Marsella, CEO of Survey Lab.
"Thanks to heritage data from ERS and Envisat, integrated with Third Party Missions such as COSMO-SkyMed, and to the current Copernicus Sentinel satellites, we are able to better understand deformation patterns before they become critical for the stability of buildings, thus improving public awareness on safety issues in large urban areas," concluded Dr Marsella.