SAR Technology: Beyond the Visible Spectrum

The advancements in synthetic aperture radar (SAR) technology and its declassification has enabled satellites to offer illuminating insights into Earth’s complexities and modern warfare with its constant observation of almost any location on the planet

By Girish Linganna

Opinion

Synthetic Aperture Radar (SAR) enables satellites to send radar signals to the ground and analyse the echoes that come back. This technology can see through clouds, making it a powerful tool for observing the Earth’s surface. At any given moment, clouds cover about two-thirds (or 67%) of the Earth, blocking conventional satellites from viewing large portions of the planet.

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However, with the declassification of synthetic aperture radar (SAR) technology, satellites can now ‘see’ the Earth’s surface even in darkness, through clouds and smoke from wildfires. This technology offers a clear and constant view of our planet, revealing detailed changes on Earth’s surface.

Previously, this technology was limited to a few large commercial satellites. Now, start-ups like GalaxEye in India are using it with groups of low-cost nanosatellites in low-Earth orbit. The aim is to offer constant observation of almost any location on Earth, benefiting everyone from non-government organisations to military clients.

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“SAR satellites can cover more area and provide higher-resolution images than optical satellites, whether it is day or night,” says Holly George-Samuels, an associate scientist at QinetiQ, a security and defence company, as reported by BBC. “You don’t have to wait for clear skies or for the rain to stop. If you need information, you can get it immediately and it will be better than an optical image.” With centimetre-level resolution, you can even spot sheep tracks in the grass.

Eric Jensen, CEO of the US branch of the Finnish startup, Iceye, recalled that, in early-2018, they were told it was impossible to create a small SAR satellite and, even if it was possible, a satellite that small would never perform to satisfaction, BBC reports. In true entrepreneurial spirit, we responded, ‘Thanks for your feedback, but we’re going to try it anyway’. Now, we’re building satellites that are 100 times cheaper than they were 20 years ago and launching them four to five times faster,” says Jensen.

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With the declassification of synthetic aperture radar (SAR) technology, satellites can now ‘see’ the Earth’s surface even in darkness, through clouds and smoke from wildfires. This technology offers a clear and constant view of our planet, revealing detailed changes on Earth’s

In 2022, SAR satellites were used to show the extent of the Russian invasion of Ukraine as it unfolded. The following year, they tracked the spread of wildfires in Hawaii and assessed the damage almost in real time. This year, they were used to quickly reveal the damage caused by the Baltimore Francis Scott Key Bridge incident.

Their potential goes beyond this. NASA Earth scientist and SAR specialist Cathleen Jones uses the satellites to monitor various types of hazards, as quoted by BBC. Most of California’s water is in the north, but most of its population lives in the south. The California Aqueduct, a large waterway, moves water from the north to the south. SAR provides the capability to detect even small movements in the aqueduct—a channel or pipeline for water—down to the barest centimetre.

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Similarly, she has used this technology to understand why sinkholes—cavities in the ground caused by water erosion, leading to the collapse of the surface layer—form in such coastal areas as New Orleans.

The 2024 hurricane season officially starts on June 1 in the Atlantic Ocean, the Gulf of Mexico and the Caribbean Sea, with up to 25 named storms expected. SAR technology could play a crucial role in the cleanup efforts—removing debris, repairing damage and restoring the areas affected—afterwards. All the satellite images are minutely inspected to detect oil spills.

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Jones does this by measuring how light reflects off surfaces. Oil makes the surface appear flatter and darker in the images. This technology helps us quickly find the oil and where it is heading, says Jones. “It’s especially dangerous when an oil slick moves onto shore into wetlands or populated areas.”

In 2022, SAR satellites were used to show the extent of the Russian invasion of Ukraine as it unfolded. The following year, they tracked the spread of wildfires in Hawaii and assessed the damage almost in real time. This year, they were used to quickly reveal the damage caused by the Baltimore Francis Scott Key Bridge incident

So how does it work? Unlike optical satellites that depend upon sunlight to light up an area on Earth, SAR satellites generate their own ‘sunlight’ by sending strong microwave signals—electromagnetic waves with wavelengths that are shorter than those of radio waves but longer than those of infrared radiation (1 GHz-300 GHz) and commonly used in radar, communication, and cooking—to the ground. These signals are not affected by weather conditions.

By carefully analysing the reflected signals, SAR creates a highly detailed radar image of the area. With frequent passes over the same location, SAR can detect changes on the ground as small as a fingernail. However, these images look very different from the ones we see on Google Earth—a digital mapping service that provides satellite images, maps and 3D representations of Earth’s surface.

SAR images, unlike optical ones, are high-resolution maps showing how much the ground reflects radar signals. So, it is harder to understand, says BBC quoting George-Samuels. Understanding and interpreting these images require special training. However, AI can be trained to interpret these images for us.” But the technology is more about gathering data than capturing images.

Much of the interest in SAR began with a patent awarded in 1954. The declassified Project Quill satellite, launched by the US in 1964, is believed to be the first to use this groundbreaking technology. However, it is only now, almost 60 years later, that SAR is finally getting the attention it deserves.

After all of 70 years have passed since the first patent, the lowering cost of components has made a marked difference. The main thing is the ability to miniaturise components to quickly build small, cost-effective satellites and this reduces the overall cost, said Beau Legeer, director of imagery and remote-sensing at software company Esri, to BBC. Additionally, launching these satellites is now easier, cheaper and faster than ever before. The availability of venture capital to fund startups and the early success of SAR technology in various applications have also contributed to its growth.

SAR images, unlike optical ones, are high-resolution maps showing how much the ground reflects radar signals. So, it is harder to understand. Understanding and interpreting these images require special training. However, AI can be trained to interpret these images

One of SAR’s major advantages is that it is not affected by such factors as sun angles and shadows that impact optical images. This consistency makes SAR a reliable data source, ideal for artificial intelligence (AI) and machine learning (ML) applications.

According to Jensen, the shift in the US government’s attitude has been crucial for advancing SAR technology. The US government had once tightly controlled this technology so that enemy countries could not benefit from its use by surveying allied military installations in high resolution in the daytime, or at night, he told BBC. As a result, European nations and Canada took the lead in commercialising the technology.

Their satellites cost $400 million to $500 million each, took four years to build and needed two years to fine-tune once in orbit. Instead of restricting the development of this new technology, the US has now embraced it. The US government is now much more open to collaborating with allied nations that develop key technologies like this than ever before.

Cathleen Jones told BBC she believes the main reason SAR is becoming prominent now is technological advancements. “But this data was earlier very expensive. When the European Space Agency and NASA made their data free to use, it suddenly became much more popular,” she explained. Similarly, all the data from the advanced Nisar satellite, a joint project between NASA and the Indian Space Research Organisation (ISRO), will be free to use once it launches.

Others have a different perspective. “I’m not sure if ‘revolution’ is the right word,” says Bleddyn Bowen, author of ‘Original Sin: Power, Technology and War in Outer Space’, as reported by BBC. “It’s been used by the military and intelligence communities for a long time. It’s only getting more attention now because there are a few commercial providers and the data is more accessible to the government and private industry than before,” says Bowen.

However, the future of SAR technology depends on solving the engineering challenge of making larger antennas and solar panels for satellites, while still keeping the satellites small enough to be easily launched—a tough physics challenge. “A large antenna is very useful for improving image quality,” Frank Backes, CEO of Capella Space, told BBC.

Much of the interest in SAR began with a patent awarded in 1954. The declassified Project Quill satellite, launched by the US in 1964, is believed to be the first to use this groundbreaking technology. However, it is only now, almost 60 years later, that SAR is finally getting the attention it deserves

It will also rely on the development of orbital communication networks, such as Amazon’s Kuiper, which other spacecraft in low-Earth orbit (LEO) can connect to. This would give them the capability to send data directly to the user, said Backes, which would cut down the time from a couple of hours to less than a quarter.

Communication networks, such as Amazon’s Kuiper, consist of a large group of small satellites orbiting Earth, known as a satellite constellation. These satellites work together to provide Internet and data services across the globe. By communicating with each other and ground stations, they can transmit data quickly and reliably. Additionally, these satellites can connect to other satellites in space, not just those within their own network. This inter-satellite communication enhances the overall efficiency and reach of the network, helping deliver Internet access to remote, or underserved, areas that lack traditional infrastructure. In essence, Kuiper aims to create a global, space-based network for high-speed Internet.

But the future of this technology heavily depends on AI. Whatever its other drawbacks, AI will do a great job of extracting information from the data and presenting it, feels George-Samuels. In the end, supporters say SAR will benefit society by improving the efficiency of supply chains, making agricultural yields more predictable and, perhaps most importantly, helping keep people safe during floods or wildfires.

George-Samuels told BBC she believed that SAR would enhance environmental monitoring and help save lives. Others have even grander visions. “It will bring transparency worldwide,” says Backes. “In conflicts, having readily available information will clear up confusion for the public, as we’ve seen in the Russian-Ukrainian conflict.”

But not everyone supports this technology. Some people worry about its potential dangers, such as invading privacy, being used for corporate spying, or even planning terrorist attacks.

The future of SAR technology depends on solving the engineering challenge of making larger antennas and solar panels for satellites, while still keeping the satellites small enough to be easily launched—a tough physics challenge. The future of this technology heavily depends on AI. Whatever its other drawbacks, AI will do a great job of extracting information from the data and presenting it

Is hype also a factor? Private imaging companies had created the hype that these would provide total transparency. But no, says Bowen. “We’ll be get a warning before anything happens, but we’ll never have complete transparency or full information because the images aren’t like live video and don’t provide all the details you might need.”

In January 2022, everyone could see Russian troops gathering at Ukraine’s border, but no one could read Russian leader Vladimir Putin’s mind to know if a war was coming. We also never received any images or information about what was happening on the Ukrainian side. The US had complete control over what was shown.

(Source: BBC)

-The writer is a Defence, Aerospace & Political Analyst based in Bengaluru. He is also Director of ADD Engineering Components, India, Pvt. Ltd, a subsidiary of ADD Engineering GmbH, Germany. You can reach him at: girishlinganna@gmail.com