ESA Sentinel-1D delivers first high-resolution images
esa.int126 points by giuliomagnifico 2 days ago
126 points by giuliomagnifico 2 days 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.
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.
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'.
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.
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...
Typically you will get an image pair for an area every 6-12 days. The phase used in interferometry is massively affected by atmospheric conditions, which can vary a lot in this time, and are difficult to correct for. So, one pair is often not enough for this. But if you look at a bunch of pairs for that area over a longer time period, you might be able to correct for the atmospheric effects and get your differential height map. You can get more accurate elevation models 'out of the box' with different systems, e.g., the SRTM (one of the most well known publicly available global elevation maps) [1] was made with insar but 2 antennas on one craft, and Germany's TanDEM-X [2] is a pair of satellites flying in formation a few hundred meters apart, capturing the same area at the same time.
[1]: https://www.earthdata.nasa.gov/data/instruments/srtm [2]: https://en.wikipedia.org/wiki/TanDEM-X
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
The Copernicus data browser is quite nice, even though they like to sit on possibly sensitive images for long periods of time.
"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.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.
Is there a specific name for the vaguely fractal nature of the cliff formations in the Tierra del Fuego shot?
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...
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.
High resolution images, but they decided to disable zoom on mobile. I don't understand why anyone does that.
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.
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.
They're not the highest resolution, but they're still high enough resolution that I can't see the details without zooming in.
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.
Also, I don't understand why browsers don't let me override that.
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.
Awesome. Somehow I've missed them introducing that, as a long-time Firefox Android user.
And frankly it's in the wrong place if you ask me.
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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
Yes, because it’s correct and informative and on-topic. What’s your track record, {1 comment, 0 posts, account 4 hours old}?