ICEYE adds 25 cm SAR satellites to its constellation

Finland’s ICEYE has deployed two new synthetic aperture radar (SAR) satellites with 25 cm imaging capabilities to its constellation, according to a 21st December press release. The two satellites were launched as part of the Bandwagon-2 rideshare mission with SpaceX marking the 40th satellite deployed by ICEYE since 2018, and the ninth in 2024 alone. 

The satellites have been deployed to a mid-inclination orbit, “Polar orbits go from pole to pole and mid-inclination orbits have a trajectory around the equator,” an ICEYE representative told Calibre via email. “They serve different needs. In a simplified way, one can say that the Earth is most inhabited around the equator, which makes a good case for the mid-incline orbit,” the representative added. 

ICEYE maintains satellites in both a polar and mid-inclination orbit to serve different customer needs, the large quantity of satellites provides a high revisit rate, which is measured in how regularly a satellite passes over a given point. “Revisit rates depend very much on the specific area of interest. Some areas have much higher revisit rates than others due to the location and the orbits,” ICEYE explained. As of September 2024, ICEYE’s constellation had 21 satellites in orbit allowing a daily revisit time for a lot of locations, however, the company plans to increase the constellation to 48 satellites providing twice daily revisit times.

SAR satellites work by sending electromagnetic waves to the ground where they bounce off the objects and terrain returning to the satellite. There, the difference in the strength of the signals and their timing is processed and turned into an image. This enables SAR satellites to build a picture of what is happening regardless of weather or the available light – which is also why SAR is used for reconnaissance on AC-130U gunships and other aircraft. 

The resolution (essentially the quality) of the image depends on the radar frequency used. “With a maximum radar bandwidth of 1200 Mhz right now (this is currently the legal limit for all radar satellites commercially available), radar satellites can achieve 25 cm resolution. Earlier generations of ICEYE satellites can do 1 m and 50 cm, because the radar bandwidth was 300 and 600 MHz respectively,” the ICEYE representative explained. This means that the greater the bandwidth, the more detail will be discernible from the generated image, this is important for SAR reconnaissance as the images can lack detail or clear sharp edges when compared to optical imaging. 

This image from ICEYE shows how SAR imagery is represented after processing. It has captured naval vessels at a base. This image shows how SAR intelligence may lack clarity, necessitating the greatest resolution possible. Credit: ICEYE.

There are two different modes of imaging for ICEYE SAR satellites, according to the European Space Agency’s eoPortal website; the first is Stripmap, which continuously draws imagery over a strip of land up to 30 km wide and 50 km long. The image will be the same quality throughout, but may lack the detail of the second imaging mode, Spotlight, which repeatedly steers the satellite’s antenna at the same 5 km square as the satellite flies over the area leading to a much higher resolution image.

In addition to nine satellites in 2024, ICEYE has also added an application programming interface (API) for its satellites which enables users to task satellites to collect imagery of certain areas. “The benefit of the API is that there is no human interaction needed and for customers with a high volume of data, this is a great benefit,” ICEYE said. Tasking does not change the trajectory of the satellites, but instructs them to collect imagery of a given area as they travel over it. 

Calibre comment

Space-based reconnaissance has been important for defence and security since the 1960s, when it was conducted with cameras and films that were developed upon their return to Earth. It proved invaluable in understanding the extent of the USSR’s naval modernisation, for example, and has supported battle damage assessment and targeting since the 1980s. However, now, many states are looking to space-based reconnaissance for close to real-time targeting for long-range precision strike weapons. This makes the all-weather capabilities of SAR satellites particularly important, especially if militaries decide that deploying these missiles is key to winning a war. The target type can influence the required revisit times, tracking large groups of ships in the Indo-Pacific, for example, would require a very high revisit time, whereas identifying large bases or critical infrastructure can be done with daily revisits. 

By Sam Cranny-Evans, published on 28th December 2024.