I was curious what instruments this use, looks like a special form of radar? Does this mean it effectively gives us very accurate height maps regardless of cloud coverage, and is able to differentiate between what surface material it's seeing?

> Radar instruments can image Earth’s surface through clouds, precipitation, regardless of sunlight, making them particularly well suited for monitoring polar regions. The Sentinel-1C and -1D satellites also carry an Automatic Identification System (AIS) instrument – improving the mission capacity to detect ships and sea pollution. The Sentinel-1D AIS was also activated as the satellite passed over Antarctica capturing the presence of ships in these extreme areas.

What you can get in a single image are 5.5cm wavelength microwave backscatter - this means surface materials can be differentiated by looking at texture differences at that scale. So - tarmac vs a ploughed field, for example. There's 2 polarizations as well, so you can identify e.g. vegetated areas also, which scatter the signal in a different way.

A single image from Sentinel-1 won't give a height map directly, but a pair can using interferometry (InSAR), as the phase of the backscattered signal is also measured. With that you can derive something about the terrain. It's not super accurate though for absolute height maps.

And yes the signals pass through cloud and it works at night.