In 2013, the National Snow and Ice Data Center received 50 cardboard boxes with 500 rusted and dust-covered cans; in each can, there were 150 meters of 35mm films. The images captured by the seven Nimbus weather satellites (put into orbit since 1964) today are a reference and a comparison for the data collected by the dozens of SAR satellites in orbit that capture, in detail, the earth’s surface.
The Arctic (left) and Antarctica seen by the Nimbus-1 satellite.Source: National Snow and Ice Data Center / Disclosure
“Wherever you look on Earth, you see something new. It’s a bit like children in a candy store, ”said NASA design scientist Paul Rosen, a pioneer in the use of Synthetic Aperture Radar Interferometry or InSAR.
The SAR technique, in fact, is not new (it dates from the 1960s), and has emerged as a military tool for aerial reconnaissance and mapping. Roughly speaking, it is based on the sending of microwave pulses and echo recording, regardless of whether the area to be analyzed is covered with clouds or if the satellite travels at night.
Theoretically, the larger the radar antenna, the more echoes are captured, resulting in sharper images. However, there is a limit to this size; so the researchers, instead of designing a huge antenna, created an artificially large antenna, combining the signals received as the satellite moves through space (so the opening is “synthetic”).
SAR images are designed to monitor changes in the soil, such as the creation of camps by terrorist groups, oil spills in the ocean, the dumping of icebergs or deforested areas. InSar, on the other hand, takes a sharper look to perceive subtle changes (in the millimeter scale) between one image and another, capturing phase differences in the return signal before it even reaches the antenna.
Through InSAR, it was discovered that the caldera of the Ethiopian volcano Corbetti is not inactive as previously thought.Source: University of Oxford / Disclosure
These satellites are no longer restricted to scientific use; there are already 50 in low Earth orbit, monitoring from volcanoes that were thought to be asleep to plantations, cities and icebergs.
“They are showing up everywhere,” he told the Science Magazine the analyst Dáire Boyle, who accompanies the space industry for the consulting firm Evenflow. Analysts estimate the SAR market at around $ 4 billion and expect that number to double in the next 5 years.
Dares Technology is a company that interprets SAR satellite data for customers as mining companies.Source: Dares Technology / Reproduction
One square meter per hour
For decades, the use of InSAR has been limited: there were few satellites and their orbits were unstable, making it impossible to track events in real time. This changed when the European Space Agency (ESA) launched, in 2014, the Copernicus program to “observe the Earth in a global, continuous and wide-ranging manner”.
The program launched the SAR Sentinel-1a and 1b satellites, which scan the planet every 12 and 6 days, respectively. In orbit for almost 7 years, they provide records that are now also analyzed by sintético intelligence.
While more countries (such as Italy, Japan, Argentina and China) are already scheduled to launch InSAR satellites soon, in January three satellites of a new class have risen into space. Creation of Iceye, a Finnish SAR startup, they are the first in a constellation of a hundred that should, in the coming years, take images of every square meter of the Earth every hour.
This year, it is planned to launch at least eight more satellites, which will allow us to revisit most of the globe at least once a day.