Sentinel 1C is in orbit. Or the “cultural revolution” of Sar, brought by Copernicus.

According to Diego Calabrese of Thales Alenia Space, the radar technology in which Italy is an undisputed leader has gained traction thanks to the European “Sentinels,” which enable action in emergency situations and drive business growth.

BY EMILIO COZZI

A world in shades of gray: this is how the Earth’s surface appears in the radar images that satellites in orbit deliver to the ground every day. Nothing even close to the evocative vision of the “Blue Planet”; in fact, the “matrix” often doesn’t even allow us to recognize the map of a place.

When it’s not our eyes that need to “see,” everything becomes less beautiful. This doesn’t mean it can’t be more useful: the Sentinel 1C satellite launched on December 5 aboard a Vega C rocket, which returned to service after a two-year painful hiatus. The satellite carried a Sar instrument (short for “Synthetic Aperture Radar”): nothing particularly new, but it’s worth emphasizing that this is a technology where Italian expertise has no rivals. Thanks to Europe, it has now become widespread and sought after worldwide, used in Earth observation missions.

Because observing doesn’t always mean seeing.

“The interpretation of a photograph comes naturally to us. A microwave view, on the other hand, is more complex; we’re not used to it,” explains Diego Calabrese, director of the Observation Systems department at Thales Alenia Space. “Typically, anyone starting with space technology initially relies on optical systems, which are intuitively simpler. But thanks to the widespread use and significant advantages of SAR over optical systems, at night or in cloudy conditions, the taboo of SAR being a niche technology has been broken and many governments are changing their approach.”

The Sar Pair is Back in Orbit

The launch of Sentinel 1C marks the restoration of full operational capability for the Copernicus constellation, following the failure that shut down Sentinel 1B in 2022. Together with Sentinel 1A, the radar systems will now resume scanning the Earth’s surface with a halved revisit time (the interval between two passes over the same area). “The portion of the Earth’s surface, or swath, that it covers is limited because, when flying over a larger area, you need to decide where to observe,” explains Calabrese. “However, the response time is 12-24 hours for any location in the world, as we can steer the observation in case of emergencies.” Emergencies are, in fact, one of the most important applications of this instrument.

The functioning of Sar is similar to that of an ecodoppler: the antenna “sweeps” the ground with a microwave beam, which bounces back and is collected by the satellite’s sensor. This allows for the creation of a three-dimensional map of the terrain, including human-made structures. “In Italy, the big push for microwave technology came with the 1980 Irpinia earthquake,” says the engineer from Thales Alenia Space. “There were clouds, and rescuers were driving along roads only to discover they had collapsed; they didn’t know where to go. If a system like the current one had existed, rescue efforts could have been better coordinated. Today, the emergency mode is standard procedure in any type of disaster: it helps detect the extent of damage and the state of infrastructure, including roads.” Another unique feature in the case of earthquakes is the ability to precisely identify fault lines by observing the deformation of buildings.

The true strength of Copernicus lies in the continuity of its database, which the Sentinel 1 satellites have steadily built. In emergencies, this archive is an invaluable resource, even when other Sentinels or satellites from constellations such as Cosmo-SkyMed or TerraSar-X are the first to pass over affected regions.

For saving lives, Sar is a superpower: radio waves penetrate clouds more easily. Moreover, as an active instrument, the radar works effectively even at night, since it doesn’t rely on visible light but rather on the echo of the electromagnetic waves it uses to “illuminate” the terrain.

How the World is Changing

What emerges are like frames from a film. By comparing two observations taken over time, the result is revealed: what has moved or changed on the Earth’s surface.

Sar can “detect” the movement of a slope, a bridge, or a building. “Monitoring the displacement of infrastructure is one of its main applications. It allows us to check how stable they are, with accuracy down to the centimeter,” adds Calabrese. In the case of climate events like floods, the physics of the system itself (a bouncing wave) makes it possible to identify submerged areas.

Another service leverages the polarization of electromagnetic waves for precision agriculture. “Precision farming using satellite systems is gaining traction, also thanks to companies offering such services. The data can determine whether crops are growing correctly, whether there is moisture or not, and help decide where to irrigate. Typically, hyperspectral sensors are used, but they don’t have high resolution. SAR is starting to develop similar capabilities. There are relationships between the signal response, combining polarization with the band, and the state of crop growth. The fusion of Sar and hyperspectral data improves accuracy,” Calabrese explains. These applications are particularly useful on a large scale, for monitoring extensive farmlands in Canada or South America. They are less suitable for more intensive or smaller areas, where the same service can be carried out at a fraction of the cost using drones.

The Revolution and Its Future

According to Calabrese, in this field, Europe has shown the world how it’s done, and the world has followed the “Sar revolution,” which is still ongoing. This started with the Esa and European Union’s policies on Copernicus data and observations, which are freely accessible and usable by anyone, including companies for commercial purposes. “With institutional demand, both national and from Copernicus, a cutting-edge technology has been developed in Europe, particularly in Italy. This has helped spread the culture of Sar, breaking the taboo that radar is too complex to interpret. As a result, services and applications have been developed, and it is no longer a niche technology. Sar is now used by countless companies for a wide range of applications.”

Looking at costs brings us to a critical point: what will happen in the coming years. According to the director of the Observation Systems department at Thales Alenia Space, much will depend on revisit time. “In the future, I see two major trends emerging: cutting-edge applications, especially for governmental needs, and at the same time miniaturization of technologies and cost reduction.

In this context, we are developing Iride, which aims to reduce both mass and costs. This will allow for multiple launches with the same rocket. In communications, this approach has been used for years. It’s the strategy adopted by Elon Musk. Starlink was a turning point in this regard.”