A New Satellite Can Peer Inside Buildings, Day or Night • Hacker News Board

Re: A New Satellite Can Peer Inside Buildings, Day or Night

#91

Post by geomark » Fri, Dec 18, 2020, 5:41 AM UTC

SirLuxuryYacht wrote: post #84

grendelt wrote: post #36

Earlier quoted context omitted.

Almost any depth. A big steel tube is going to displace water. Once you have some baseline measurements (of known underwater landforms), then small imperceptible variations would stick out.

Not possible. The uncertainty of bathymetry in areas only mapped using gravity is larger than the dimensions of a sub. Even in very well mapped areas, think of the effort in the Indian ocean to find MH370, this would require the assumption that the sub is moving, which is not always the case, e.g. if the sub halts propulsion and drifts with a current.

Well yes, it's the surface disturbance of the underwater wake that they are detecting. So the sub has to be moving under its own power.

But there is no need for high resolution and the wake of the sub stands out starkly even with a large field of view. So I'm not sure it can evade detection by halting propulsion and drifting. The point at which it halted would be known and it would be detected as soon as it restarted, unless it was carried by an unknown current far enough to be out of view of the satellite.

Re: A New Satellite Can Peer Inside Buildings, Day or Night

#92

Post by geomark » Fri, Dec 18, 2020, 5:56 AM UTC

garettmd wrote: post #44

raws wrote: post #17

Earlier quoted context omitted.

I think he's just alluding to the fact that there's already better ones out there for other countries, maybe even better for secret military bodies.

And just because they have that capability, doesn't mean they can "legally" use it. The posted article says that it can do a better resolution than that 50cm, but didn't specify how much better.

ICEYE's website says high res (25cm) imaging is commercially available. Even has some sample 25cm res images available for download at the bottom of this page (I have not downloaded so can't vouch for it) https://www.iceye.com/satellite-data/blog/new-benchmark-in-i...

Re: A New Satellite Can Peer Inside Buildings, Day or Night

#93

Post by [deleted] » Fri, Dec 18, 2020, 6:29 AM UTC

unchocked wrote: post #87

baybal2 wrote: post #79

Earlier quoted context omitted.

> Note that these 50cm image resolutions are limited by law, not technology. By physics, and computing power. For any stable circular orbit, a satellite can only fly that fast, and the radio window would only pass so much of radio spectrum.

From the article, the 50cm resolution is by law. Physical limits also exist, and one presumes that military hardware is operating closer to them.

[deleted]

Re: A New Satellite Can Peer Inside Buildings, Day or Night

#94

Post by marsokod » Fri, Dec 18, 2020, 9:01 PM UTC

baybal2 wrote: post #79

unchocked wrote: post #71

Note that these 50cm image resolutions are limited by law, not technology. The US military of course has superior technology, and its resolution is unlikely to be limited by statute. The NRO Topaz satellites are the successful radar development of the two prong Future Imaging Architecture (the optical component failed, which was to be the successor to Keyhole [of which the Hubble Space Telescope is derived]) should b…

> Note that these 50cm image resolutions are limited by law, not technology. By physics, and computing power. For any stable circular orbit, a satellite can only fly that fast, and the radio window would only pass so much of radio spectrum.

Capella's competitor Iceye has already achieved 25cm. Physics limitations are even lower than that.

But you are right talking about computing power. SAR work in a very different way from optical imagery and data generation/processing is quite a huge difficulty.

Re: A New Satellite Can Peer Inside Buildings, Day or Night

#95

Post by baybal2 » Fri, Dec 18, 2020, 9:59 PM UTC

marsokod wrote: post #94

baybal2 wrote: post #79

Earlier quoted context omitted.

> Note that these 50cm image resolutions are limited by law, not technology. By physics, and computing power. For any stable circular orbit, a satellite can only fly that fast, and the radio window would only pass so much of radio spectrum.

Capella's competitor Iceye has already achieved 25cm. Physics limitations are even lower than that. But you are right talking about computing power. SAR work in a very different way from optical imagery and data generation/processing is quite a huge difficulty.

With free flying satellite SAR, the resolution is dependent on how fast the satellite can fly before it gets the return signal, and this is predetermined by orbital velocity.