[HN Gopher] ESA Sentinel-1D delivers first high-resolution images
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ESA Sentinel-1D delivers first high-resolution images
Author : giuliomagnifico
Score : 61 points
Date : 2025-11-30 17:37 UTC (5 hours ago)
(HTM) web link (www.esa.int)
(TXT) w3m dump (www.esa.int)
| whitehexagon wrote:
| 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 wrote:
| 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
| hermitcrab wrote:
| Pretty cool. But it gives me some sort of existential vertigo.
| hak8or wrote:
| 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.
| lmc wrote:
| 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.
| leoedin wrote:
| 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.
| hermitcrab wrote:
| 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'.
| mkl wrote:
| High resolution images, but they decided to disable zoom on
| mobile. I don't understand why anyone does that.
| cess11 wrote:
| 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 wrote:
| _" 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.
| OgsyedIE wrote:
| Is there a specific name for the vaguely fractal nature of the
| cliff formations in the Tierra del Fuego shot?
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