hckrnws

High resolution images, but they decided to disable zoom on mobile. I don't understand why anyone does that.

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.

Synthetic aperture radar is basically building a bitmap of radar reflectivity. So what you get looks a lot like a photo. You can end up with very non-photo artifacts though - blown out pixels caused by corner reflectors, bright things can result in ghost copies in multiple places and if there’s other radar operating in the same frequency bands it can end up on the picture.

The core idea is that you send out pulses as you pass over the ground and then record the echoes. You can create an image by - for each pixel in the image - working out the response you would expect to receive back and correlating that with the actual responses you saw. That gives you a reflectivity value. You can do it in multiple polarisation to better distinguish things.

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.

The Copernicus data browser is quite nice, even though they like to sit on possibly sensitive images for long periods of time.

https://dataspace.copernicus.eu/browser/

I used to enjoy clicking through to the ESA Sentinel images, but then they kinda dried up for a while, or it was very hit and miss for updates. It would be nice to have regular daily or weekly upload. Our planet is so beautiful, as many of these Sentinel images show.

While we're talking about cool ESA achievements, the view of our universe Euclid gives us is incredible.

Check out this video they made if you want your mind blown: https://www.youtube.com/watch?v=rXCBFlIpvfQ

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The EU tends to do very well in earth observations compared to the U.S. as some would say they are overall better. A lot of earth science and climate related fields tend to do better in the EU as well. For example, hurricane models tend to outperform their U.S. counterparts.

typical content that totally passes the moderation guidelines and community voting