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Homemade polarimetric synthetic aperture radar drone
- throwup238 2y agoThis is why I read HackerNews. Every month there’s a new article that improves my suburban missile defense system* and helps guarantee that my neighbors will never let their dogs poop on my lawn ever again. Terrain mapping my neighborhood so that my rockets can navigate to the right offender has always been a challenge. Now I can just use drones! * It’s a defense system with missiles, not a defense system against missiles. That would be silly.
- gessha 2y agoThere’s that and there’s also anti-drone jamming. What a world we live in.
- samplatt 2y agoA lot of anti-drone jamming is severing the wireless communication between a drone and its operator. In most of the write-up, these drones were on pre-planned autonomous routes, and would thus not be affected. Unless you also had anti-radar installations :-) Or hell, some kinda highly-illegal and mostly-unfeasible microwave gun or multi-watt CO2 laser that you could point at a drone and bring it down.
- temp0826 2y agoMaybe old school (but sort of James Bond-esque?) but I really dig these shotgun shells that shoot nets https://www.lesslethal.com/products/12-gauge/als12skymi-5-detail https://www.lesslethal.com/products/12-gauge/als12skymi-5-de...
- pjc50 2y agoUkraine and Russia are apparently building drones with fiber-optic tethers to defeat this. Like the old wire-guided missiles. https://www.businessinsider.com/ukraines-drone-makers-producing-fiber-optic-weapons-didnt-think-possible-2025-2 https://www.businessinsider.com/ukraines-drone-makers-produc...
- iugtmkbdfil834 2y agoA new cat and mouse game.
- alashow 2y agoI wonder why spool of fiber optic cable is on the drone vs with the operator..
- pbmonster 2y agoDrag and fibre tension. In the former case, you have close to zero for both. In the latter, you're dragging 2km of line behind a small aircraft, risking the line getting snagged by something on the ground.
- nullc 2y agoI find that rogue poopers are most effectively addressed with loitering munitions. It's well known that immediate feedback is critical in animal conditioning.
- Nevermark 2y agoHow about a small laser with enough power for a 100ms burst in the non-visual spectrum that vaporizes 1mm radius, 0.5mm depth of protein, through 1-5cm depth of hair? No sense sacrificing any hardware. Zero resource attrition and imperceptible evidence of action is the name of the game. Match that with a spot of sound out of human hearing range and you can clear the enemy of its own accord far beyond your legal and overt action spheres. If a close neighbor’s unit stays clear but expresses its dismay regarding warning sounds too loudly, well, this works for that too. We are talking about nuisance bears and moose, right?
- nullc 2y agoI lost a little chunk of flesh to a pulsed laser, didn't even know I was injured immediately-- the wound didn't hurt until later. Clearly the solution is laser ignition of napalm-- don't want to accidentally catch the drone on fire, so the laser can be timed to fire once the stream is clear of it.
- throwup238 2y ago> laser ignition of napalm Now we’re talking! Unfortunately I couldn’t figure out how to deploy something as viscous as napalm through my sprinkler system. I’ve been reduced to dropping it from a helicopter, the old school way.
- nullc 2y agoFour words: Diesel engine fuel injection.
- Grosvenor 2y agoThese might help. Tactical and Strategic Missile Guidance, Seventh Edition https://www.amazon.com/Tactical-Strategic-Missile-Guidance-Seventh/dp/162410584X https://www.amazon.com/Tactical-Strategic-Missile-Guidance-S... Tactical missile warheads https://www.amazon.com/Tactical-Warheads-Progress-Astronautics-Aeronautics/dp/1563470675 https://www.amazon.com/Tactical-Warheads-Progress-Astronauti... Fundamentals of Astrodynamics https://www.amazon.com/Fundamentals-Astrodynamics-Second-Dover-Physics/dp/0486497046/ref=sr_1_1 https://www.amazon.com/Fundamentals-Astrodynamics-Second-Dov...
- daemonologist 2y agoWoah, prices have gone up for that Missile Guidance book. Used copies were going for like $15 a couple of years ago.
- contingencies 2y ago$170 for 2 volume hardback set @ https://arc.aiaa.org/doi/book/10.2514/4.105845 https://arc.aiaa.org/doi/book/10.2514/4.105845 .. fairly standard price these days for technical books.
- secondcoming 2y agoI own the Tactical and Strategic Missile Guidance book. I only bought it because I have a passing interest in this stuff and really couldn't believe this sort of book is publically available.
- philipkglass 2y agoEvery terrifying technology that people worry can be propagated by AI or terrorist manuals is already sitting on a university library shelf. Most of it already available via Sci-Hub or Library Genesis. I have documents on nuclear weapons that would have been top secret 50 years ago.
- iugtmkbdfil834 2y ago
- mmusson 2y agoThe missile knows where it is at all times. It knows this because it knows where it isn't...
- transistor-man 2y agoStellar work! This is such a wonderful writeup!
- geokon 2y agoThis is actually the first time I've seen the SAR algorithm explained. Every SAR project I've seen glosses over this part. Wonder if anyone else has seen more resources on this? Going to try to digest the linked paper.. https://topex.ucsd.edu/rs/sar_summary.pdf https://topex.ucsd.edu/rs/sar_summary.pdf And in the end it seems you can bypass a lot of the position problems with autofocusing! First time seeing this part too :))
- celegans25 2y agoHenrik has a blog post about a SAR radar he made from a couple years ago that goes into a bit more detail about how it works https://hforsten.com/synthetic-aperture-radar-imaging.html https://hforsten.com/synthetic-aperture-radar-imaging.html
- mNovak 2y agoThis site [1] has pretty approachable content generally, though it looks like the SAR page is pretty short. I find it easiest to understand in the context of a conventional phased array, but that might not help if you don't already know how those work. [1] https://www.radartutorial.eu/20.airborne/ab07.en.html https://www.radartutorial.eu/20.airborne/ab07.en.html
- geokon 2y agoYeah this kind of kindergarten explanation I've seen.. This is making a bunch of simplification that aren't helpful With a phased array you're beam forming and sweeping an area of space. Your signal returns are from the beam or side lobes. You can passively beam form on Rx as well. But with SAR you're not beam forming. You're illuminating everything - the whole ground below you. And you get a return from everywhere all at once. Two equidistant reflectors will return signals simulatenously. If your flight path is between these two points, and the distance is always equal, how can you differentiate them? You're digitally beam forming on the Rx somehow but I think there is more to it
- namibj 2y agoYou can't differentiate them in that case. You'd have to fly orthogonal across the surface for~ maximum effect.
- farhanhubble 2y agoAs a DIYer myself I am awed by how much Henrik has managed to flesh out in terms of complexity: signal processing, hardware, GPU acceleration, and algorithmic optimizations. I wish the HN community had some award for such incredible feats.
- pjc50 2y agoIt's a huge amount of work. It looks like at least a PhD's worth. Huge achievement for a hobbyist.
- DoingIsLearning 2y agoThis is absolutely amazing work but I would not call him a hobbyist. Again not diminishing the work but adjusting the expectations, this output is not from a curious guy in a shed. He is a trained Electrical Engineer working as a Senior Consultant/Scientist in RF design for a Finnish Engineering Consultancy. This guy clearly has a breadth and depth of knowledge from his professional career which he brings with him into his out-of-office projects.
- Animats 2y agoYes, clearly this guy is an experienced RF designer. What's impressive is that he did the RF part, the SAR data reduction part, and the drone control part. Those are different skill sets.
- lokimedes 2y agoHe is researching this stuff for s living as well.
- deleted 2y ago[deleted]
- nodra 2y agoAn upvote doesn’t do this justice. Just an amazing write up. Thank you.
- taylorportman 2y agoIf you need a 100 meter antenna - could one be approximated using multiple drones in a coordinated 100 meter parabolic trajectory?
- mNovak 2y agoYes, if you can coordinate and hold their position to ~1/10th of the wavelength (gets challenging above a few GHz), and synchronize their transmitters/receivers with ps accuracy (feasible if there's no GPS interference). And somehow you're exchanging the raw signal components amongst all the platforms. The parabolic distribution is not at all needed in this case, you would just adjust the phase at each unit based on the distribution you have. It is a thing that's considered, mostly for very low frequencies (1-100MHz) where all the above challenges are vastly simplified, and also large antennas (potentially km) are needed for any kind of directionality.
- namibj 2y agoNo need to hold their position that accurately, just need to know, ideally in real-time.
- tecleandor 2y agoAt 6Ghz, 5cm wavelength, 1/10 would be 5mm. I think that might be a bit under regular RTK accuracy. But at lower frequencies, maybe. Or you can do several passes with the same drone and process later :D
- nine_k 2y agoIf the drones use e.g. laser rangefinders to measure the distance to 2-3 known reflectors, and maybe to each other, with sub-mm accuracy, that may be enough. Deploying an antenna that's effectively 50 or 100 m wide by lifting 10-20 drones, after some simple ground preparations, could be invaluable in many scenarios, especially for the military, of course.
- CamperBob2 2y ago
- fisherjeff 2y agoHa, wow I’ve seen plenty of SAR images from MUCH more expensive systems that don’t look nearly as good. Incredible stuff here.
- slicktux 2y agoWhat an amazing project! Great synthesis of skills to make such a cool project! I’m in awe!
- colonCapitalDee 2y ago> Recently small FPV drone prices have dropped a lot. Small 5 and 7 inch propeller quadcopters can be bought for about 100 EUR from China (not including battery and RC controller). Despite their small size they are able to lift about 1 kg or even heavier payload which is plenty for a small radar. The price dropped because China is selling these things by the truckload to both sides in Ukraine. China is benefitting from the economics of scale, Russia and Ukraine are each burning through on the order of 100,000 of these things each month and most components are sourced from China
- bloopernova 2y agoI wonder what the % breakdown is for domestic vs imported drones for Ukraine? I read recently that Ukraine was producing a lot of drones and ramping up production too, as well as using fibre-optic controlled drones to overcome electronic warfare/jamming.
- morphle 2y agoYou won't get any reliable numbers during wartime. I heard Ukrainian government recently mention they ordered a million. Hundreds of small companies (around 10 employees each) in Ukraine are making and assembling drone's right now (according to journalists who filmed them in Ukraine last month). I counted at least two dozen companies in the Netherlands, probably a few hundred all over Europe. Besides the frame that holds the 4 or six rotors together all other parts are off the shelf, mostly ordered from Shenzen. You can CNC mill a carbon fiber or aluminum frame from a single plate on an x-y flatbed cnc. I researched all this last night because I need $20K-$200k investment right now to start my own startup making unjammable autonomous kamikaze drones with 20K payload on top of 20km optical fiber spools unreeling. I think it is possible to make them lighter without fibers if you put a few thousand microprocessors in with a wafer scale integration for $500. Of course you could just make cheap drones that kill every warm body in sight[4] indiscriminately. To disable a tank you need these fiber tethered drones with bigger payloads[3][5][6]. You cab see two fiber strands still in the air in a few frames of the video. What you need is a Paul MacCready style development cycle for drones in the field. You need to be able to make 10 crashes per hour, fix the drone by replacing with off-the shelf components and try again. The programming should be live-coding like Squeak Smalltalk, no recompiling, just fix and run while you are using the software to edit itself [1] as Dan did in 1976[2] on this 5.88 mhz computer. We still code like this today but most programmers and managers ignore this in favor of terminals and simulated punch cards. Remember that it took humans 200.000 years to invent written language or agriculture, we just are not that smart. [1] https://youtu.be/NqKyHEJe9_w?t=433 https://youtu.be/NqKyHEJe9_w?t=433 [2] https://www.youtube.com/watch?v=uknEhXyZgsg https://www.youtube.com/watch?v=uknEhXyZgsg [3] https://www.youtube.com/watch?v=m3uAFBzzbTc https://www.youtube.com/watch?v=m3uAFBzzbTc [4] https://www.youtube.com/watch?v=TlO2gcs1YvM https://www.youtube.com/watch?v=TlO2gcs1YvM [5] https://www.youtube.com/watch?v=dx5_Hzbqv9s https://www.youtube.com/watch?v=dx5_Hzbqv9s [6] https://www.youtube.com/watch?v=id48aVBj9Ak https://www.youtube.com/watch?v=id48aVBj9Ak
- sllabres 2y agoWhat a impressive project and great results! Thanks for sharing here on HN.
- anilakar 2y ago> A single-channel radar can only measure the distance to a target and is unable to detect the angle of the target. Probably in that specific use case yes, but we have had parabolic dishes and slotted waveguide apertures for a long time now...
- willtemperley 2y agoThis is incredible. Having had the misfortune of trying to get Sentinel 1 toolbox working, I'm now convinced it can be rewritten from scratch.
- tomaskafka 2y agoSo, this will be seeing Russians even during the night and behind the trees? (And soon, the Chinese drones on attack through European cities will be able to hunt civilians 24/7?)
- onemoresoop 2y agoWarfare got its 21st century upgrade for sure. This is scary but hope we’ll see some countermeasures too
- cruftbox 2y agoIncredible engineering. Thanks for sharing it.