The PRNewsWire release First ICEYE-X1 Radar Image from Space Published says:
The full image transmitted to the ground from ICEYE-X1 exceeded 1.2GB of raw data and spans an area of roughly 80 x 40 km on the ground. ICEYE-X1 obtained the image in the span of ten seconds, traveling at a speed of more than 7.5 km/s and at an altitude exceeding 500 km. Matching what ICEYE simulated prior to the launch, the final data resolution from the first satellite reaches 10 x 10 meters.
Synthetic Aperture Radar works by mathematically combining radar data recored from a number of different physical locations, effectively synthesizing a large effective aperture defined by the cluster of different locations. For imaging the Earth from space, this is done using the movement of the spacecraft itself along-track, and if I understand correctly, for full 2D imaging of the surface the cross-track sampling comes either from a large physical span of antennas (see for example this question) or from closely-spaced ground tracks of completely different orbits.
The quoted passage says that the image was taken in only tens of seconds, which I believe means that there are not multiple passes used here. Since the full width of the spacecraft is only about 3.2 meters, and the wavelength is probably not much less than a centimeter, the cross-track resolution at an altitude of 500 km should be about 1km.
But the released 1600 x 1600 pixel image seems to be getting fairly close to 1 pixel resolution. I don't think this is a 1600 x 1600 km patch of Alaska.
Question: How can ICEYE-X1 capture 2D high resolution SAR images in "tens of seconds"?
edit: Looking a the images, edges facing towards the top are much brighter than those facing the bottom, suggesting reflections were recorded obliquely rather than top-down (nadir). I'm wondering if the rate of change of path length being different for different cross-track positions might be the distinguishing feature producing resolution in that direction.
- BBC News ICEYE's 'suitcase space radar' returns first image
- Ars Technica Satellites that can image Earth at night, and through clouds, near launch
- Spaceflight 101 ICEYE X1 (ICEYE POC-1)
below: "First Light" image from the press release. Open in new window to see full size. The SatCat hasn't even sorted out the payload objects of 2018-004, and one of them is already "Tweeting" images back to Earth!
caption: First ICEYE-X1 Radar Image from Space of Noatak National Preserve, Alaska