ESA Sentinel-1D delivers first high-resolution images

https://www.esa.int/Applications/Observing_the_Earth/Copernicus/Sentinel-1/Sentinel-1D_delivers_first_images_from_Antarctica_to_Bremen

by giuliomagnifico • 8 months ago

128 28 8 months ago

esa.int

whitehexagon• 8 months ago

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.

saubeidl• 8 months ago

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

hermitcrab2• 8 months ago

Pretty cool. But it gives me some sort of existential vertigo.

hak8or• 8 months ago

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.

lmc2• 8 months ago

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.

itishappy3• 8 months ago

If my understanding is correct (and I'd love to be corrected if not!), it can be used to generate super accurate differential heightmaps. It won't tell you exactly how high a peak is, for example, but it can tell you that it's dropped a few millimeters since the last time you measured.

https://en.wikipedia.org/wiki/Interferometric_synthetic-aper...

leoedin• 8 months ago

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.

hermitcrab2• 8 months ago

Ideally you want to have a large collecting area (aperture) for radar to get good resolution. But it isn't practical to put a big radar dish in space. So they use a small aperture and simulate a larger one by sweeping out an area over time and using some clever maths. Hence 'synthetic aperture radar'.

mkl3• 8 months ago

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

literalAardvark• 8 months ago

All of modern web design is about removing as much freedom from html as possible. It's infuriating.

We had zoomable, downloadable images in the 90s, with bandwidth as the only constraint.

Now I've got 50x as many pixels and I'm forced to use a bookmarklet and 2 menus to be able to see it larger than my fingernail.

magicalhippo3• 8 months ago

Also, I don't understand why browsers don't let me override that.

petee• 8 months ago

Opera Mobile has a force-allow-zoom option

mkl3• 8 months ago

These replies prompted me to go looking. Firefox Android (which I'm using) does have an option in the settings under Accessibility called "Zoom on all websites". It works!

Chrome has a similar option, which also works on this site. I expect this might break a few pages, but Google Maps and OpenStreetMap work fine, with pinch zoom zooming the map when you do it on the map.

tgsovlerkhgsel• 8 months ago

Even the high-res version (20 MB) of the Bremen image seems to be about 17-25m per pixel based on the 50m wide airport runway being about 2-3 pixels wide in the image.

Copernicus browser claims 10x10 meter pixels (which seems to be correct) but the actual resolution of the radar is supposed to be 5m-x-20m for the standard IW mode. I assume "high resolution" here means the data should have 5m x 5m resolution (Strip Map mode) which in Copernicus browser claims 3.5x3.5m pixels.

moron4hire• 8 months ago

The images on the page are not the high resolution images, they are resized as the full res versions are over 20MB. If you take the image, you'll be taken to a download page where you can get the full res version.

mkl3• 8 months ago

They're not the highest resolution, but they're still high enough resolution that I can't see the details without zooming in.

cess11• 8 months ago

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/

transpute• 8 months ago

"SARLink: Satellite Backscatter Connectivity using Synthetic Aperture Radar" (2024), https://arxiv.org/abs/2402.09682

  SARLink is a passive satellite backscatter communication system that uses existing spaceborne synthetic aperture radar (SAR) imaging satellites to provide connectivity in remote regions .. As the first technique for passively sending information bits from the ground to a SAR satellite — and with some SAR systems offering open-access data — this system could enable anyone to send information without expensive licenses or subscriptions. 

  Thus, it provides an accessible way of sending messages in areas without connectivity or in censored environments where active radio transmissions cannot be used. Furthermore, SARLink requires no modification of the satellite infrastructure.. We demonstrate our system using the European Space Agency (ESA) satellite Sentinel-1A, as the data is freely available and the system regularly images all the land on Earth .. a 5.5 ft by 5.5 ft modulating corner reflector could send 60 bits every satellite pass, enough to support low bandwidth sensor data and messages.

Peteragain• 8 months ago

Cool!

OgsyedIE2• 8 months ago

Is there a specific name for the vaguely fractal nature of the cliff formations in the Tierra del Fuego shot?

mynegation• 8 months ago

Fjords?

itishappy3• 8 months ago

https://en.wikipedia.org/wiki/Coastline_paradox

OgsyedIE2• 8 months ago

Sadly less than or equal to 2d, there, although it did lead me to Tobler's law:

https://en.wikipedia.org/wiki/Tobler%27s_second_law_of_geogr...

fuoqi• 8 months ago

I wonder if China has a constellation of similar satellites with the primary function to track the US CVBGs and provide aiming info for their "carrier killer" systems.

ESA Sentinel-1D delivers first high-resolution images

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