How does PLANETARY RADAR actually work?
ฝัง
- เผยแพร่เมื่อ 16 มิ.ย. 2024
- Arecibo was condemned a couple weeks ago, and collapsed a couple days ago as a result of a minor earthquake and well-overdue maintenance. Unfortunately, this deprives the world of its largest Radar Telescope, and radar telescopes are awesome! I've had a really hard time in the past finding good descriptions of how radar astronomy actually works - how do you take a picture of something so far away that the beam diverges by the time it gets there, and diverges even more by the time it gets back!? The answer is math and approximation. Asteroid "images" are actually not any sort of photograph, but reconstructions based on timing and spectroscopy of radar signals.
I'm really happy with how all the animations and whatnot came out, and I hope you like my explanation of delay-doppler imaging! I think it's an absolutely fascinating technique that's seen as just too counterintuitive to get a lot of recognition. Delay-Doppler images aren't really "pictures", but they are sure valuable to researchers (and every human living on Earth under threat of asteroid impact!) Share this video with anybody who wants to appreciate how important Arecibo was, and what such an awesome unique instrument was capable of.
#Arecibo #RebuildTheAreciboObservatory #Asteroids
Music in this video:
I Dunno by grapes is licensed under a Creative Commons Attribution license (creativecommons.org/licenses/...)
ccmixter.org/files/grapes/16626
Other media in this video:
Lots of public-domain NASA images, and:
commons.wikimedia.org/wiki/Fi...
commons.wikimedia.org/wiki/Fi...
commons.wikimedia.org/wiki/Fi...
commons.wikimedia.org/wiki/Fi...
commons.wikimedia.org/wiki/Fi...
commons.wikimedia.org/wiki/Fi...
en.wikipedia.org/wiki/Microwa...
commons.wikimedia.org/wiki/Fi...
commons.wikimedia.org/wiki/Fi...
commons.wikimedia.org/wiki/Fi...
en.wikipedia.org/wiki/Moon#/m...
en.wikipedia.org/wiki/Klystro...
en.wikipedia.org/wiki/Azimuth...
en.wikipedia.org/wiki/Azimuth...
commons.wikimedia.org/wiki/Fi...
commons.wikimedia.org/wiki/Fi...
commons.wikimedia.org/wiki/Fi... - วิทยาศาสตร์และเทคโนโลยี
I totally thought we used a raster scan of the asteroids to get an image. Super interesting to find out how it's actually done!
It always bugged me... Glad I'm not the only one!
The next veratasium or Vsauce. I’m very impressed by your ability to make complicated information fun and easy enough for a layman to interact with it and then ask questions. Thank you for your time and resources.
Thank you! A comparison to the greats is high praise! I was really pleased with this video in particular because it is a fairly complicated process (that I had a difficult time finding information about) and all the animations came out exactly like they looked in my head =)
@@AlphaPhoenixChannel IMO, your content is of much higher quality; the science is less clickbaity, and much more interesting, I would imagine, to other scientists and deep-in science enthusiasts.
Don't insult Alpha by calling him Veritasium.. Alpha is not an idiot :)
@@SirSpence99 Yeah, that obnoxious "Vsauce here!" style wore thin a LONG time ago.
Just discovered you, and you are a criminally underrated channel.
Good luck!
No doubt! He is one of the best on TH-cam.
Astroid is nature's exam for civilization"s space program.
Awesome video! I’ve been curious for a long time how the hell we can get an “image” of something using only Doppler shift and delay data
Drove me nuts too - turns out you need to make some assumptions!
I just want to say Thank You for doing the research.
A better title would be "How *did* Arecibo's PLANETARY RADAR actually work?"
😢
I was coming here to comment that, not surprised it’s already here
It's so unbelievably depressing seeing all of that equipment laying on the dish. And the video that was released this morning is so violent. I can't imagine being with the drone team that witnessed the fall.
😥😥
I love that you watched contact in homage ...
I've been re-watching cosmos in homage to sagan myself.
STILL UNRIVALED .... and it's not even CLOSE.
you made this complicated topic so easy to understand..... thank you 3000 ❤️ from India
Glad it helped!
Thanks for explaining delay-doppler imaging in a way that actually makes some sense!
Thanks! I’m glad you liked it! I was really proud of how this one came out cause I learned a lot while making it (I basically made it BECAUSE I couldn’t find a good visual explanation) and I was kinda disappointed in how it did on TH-cam. Glad you found it and enjoyed it!!
Makes a lot of sense. I've recently researched a little bit about radio telescopes. Turns out I slightly misunderstood the delay/shift diagrams, this explanation made it click for me.
That demonstration with the lens was very well done! Good job!
This channel is honestly such a goldmine. Just so much great content
Had me hooked from the start!! Quality content 😍
Once again, an excellent video! Thanks for making it :)
Thanks for watching it! :)
6:05 Note how the reflection comes out spherical; so on top of all the energy loss due to the beam spreading out moving _away_ from Earth (and departing the atmosphere), you now have losses from the beam being scattered everywhere on the bounce, AND THEN it has to travel ALL the way back AND back through the atmosphere, where we can listen to the faintest of echoes.
It's like trying to listen for the echo of you dropping a pin onto a pillow
You get back about a part in 10^28 of what you send. So yeah.
Great video as usual! Keep it up!
Better than building more Arecibo telescopes on Earth: build more on the Moon using the materials and craters there and some robots!
Educational, and dark. I love it!
Thanks for explaining that, I was wondering and this is a great explanation! 😀
Hey this is a really cool and useful and interesting video, right up there with the more popular channels in terms of quality. I'm super surprised this only has a few hundred likes. Have mine and keep being awesome!
Thanks! Did you get here after watching Scott Manley’s asteroid video that came out today?
@@AlphaPhoenixChannel Basically, though by searching for 'planetary radar' (where this is the top result) because I wanted to learn more about how it works. I don't think that I checked the recommended videos after Scott's video.
fantastic video as always
Well done. Found this on Reddit. Thank you.
Nice job on the video. Your graphics are better than the ones we use teaching radar that we made in PowerPoint 20 years ago :).
So that’s how it works, very interesting. I suppose this is a form of astronomy that isn’t limited by the Rayleigh criterion, the size of the dish is just important for high gain. Of course, it doesn’t work on anything outside our solar system due to the delay. I guess you could look at Doppler and delay information from short radio events like supernovae or neutron star mergers without needing to send a pulse there in the first place.
It might be feasible to get the same quality of measurements as Arecibo by using a small, amiable MW emitter with a seperate receiver nearby. Modern radio/electronics technology means we can probably make the dish smaller and still get a good SNR. Not to mention not having to suspend something above it. Actually, by having one emitter and receivers all across the world (or the other way around, or both) you could image slightly different angles of the object at once, potentially resolving that hemispheric ambiguity.
Now I want to do that with a microphone, transducer, and MCU.
If you’re trying to image things closer than two lunar distances with Arecibo, you actually have to use a separate radio telescope as a receiver because Arecibo has to physically rotate an aperture between “send” and”receive” and apparently that takes a few seconds
Great explanation!
Glad it came across! It's one of those complicated things that's simple only if you look at it from a particular way I think...
Wow!! You’re amazing man!!
Hello, I have recently discovered your channel and i'm liking it more and more as i watch different videos. In this one you are talking about the speed of light witch may not be the same in both directions, according to Derek from the Veritasium channel. I wonder if you can come up with a way to measure the speed of light 1 way ? I have an idea that involves electricity, with detectors in a spherical construct that may work but i dont have the equipment or money to build and experiment with such ideas. Hope you can come up with a way to prove it. Good luck :)
post-comment, its a radar video but both light and radio signal moves at same speed, atleast its how it is measured to be true. that is why this thought for measuring the speed of light 1 way hit me and i wanted to ask if you can try it :)
Does this system utilize some kind of subpixel estimation? Like you said that the beam becomes too wide to pinpoint a specific spot on one asteroid, but if you move the beam slightly and then compare the two images you should be able to resolve a higher resolution and perhaps even work out the north/south symmetry issue
Funny to see this now. My wife & I were less than a mile toward the coast from your location for this launch.
Super interesting! Where can I find more information about the transformation from Doppler images to X-Y maps? Thanks!
It's shocking just how little I knew about how this worked and worrying I didn't seek this information out on my own, I'm glad I'm subscribed at least
I decided to make this video after having a very hard time locating information about how delay-Doppler works (cause I just wanted to know!). There’s a good planetary society article but it’s short, and so old all the pictures are gone because of archiving. I found a few white papers and read a few journal articles talking about the reconstruction issues and whatnot and it was really interesting, but not very consumable. Hopefully this video fills a void!
I think it was in Rendezvous with Rama by Arthur C. Clarke where he proposed using space based nuclear blasts to create a large enough microwave pulse to essentially map the entire solar system all at once. (All at once being relative, of course due to speed of light.) I wonder if that might actually work.
Really cool explanation, and at least your dad is doing it, I wonder if an array of small radar telescopes operated by well equipped amateurs would be a reasonably good solution, a sort of very very large array. Maybe design a standardized unit so that different people can reliably pick up response from other transmitters?
While _optical_ telescopes with their many pixels are great at telling you the position in the sky of an asteroid (altitude and azimuth, X and Y basically) and how it moves across the sky (lateral velocity) it doesn't tell you much about how far away it is (Z) and how fast it's moving towards or away from us, which is the exactly what a _radar_ telescope is good at. So for a precise orbit you really want both!
Also: Great explanation! I was wondering how that worked :)
Gotta get those coordinates!
Glad I still got to visit Arecibo back in 2006. Couldn’t do that anymore..
Fascinating and I even managed to understand it. I think. How Does the rotation of earth (and does the telescope) affect this?
That segment at the end reminded me of the Fossil Fuelers - a (very) brief dinosaur adventure produced by ColdCrashPictures... Aaaaand now I want a collab...
The moving camera with a stationary lens is an excellent example.
this video has a totally different vibe than the latest veritasium video. I like it!
I want to be a bit more optimistic for the future. Right now we have zero technology capable of deflecting an asteroid, but we DO have ability to track and catalog, which is a necessary first step. Also we didn’t have any spaceflight whatsoever 100 years ago. Imagine how many new solutions and technologies and innovations would arise within a year of discovering an asteroid with an earth trajectory 20 years away
We are a spacefaring civilization at its most infant, and we need to grow to survive
Excellent content
Thanks!
You are winning some big points with the space nerd (the best kind of nerd) you are showing in the last videos
Just made a new playlist called "Spaaace" or something like that many "A"s and was shocked to discover that I had 27 videos in it xD
@@AlphaPhoenixChannel Will give those a watch. Thanks for the warning
1:20 ngl that was a missed opportunity for a hidden rickroll
thank you for teaching me science
Can a radar passively observe and image the sky like some sort of infrared camera, but for radio frequencies?
I think it might be possible to reconstruct them just using the delay. Reminds me of the backprojection algorithm used in medical imaging
"By the time a radar beam from Arecibo reaches twice the distance of the moon the beam is 450 km wide, which is way bigger than any asteroid." *laughs in Ceres*
solarsystem.nasa.gov/planets/dwarf-planets/ceres/in-depth/
diameter = 952 km.
Though, your point is still valid - Ceres and the other bigguns never get within twice the Moon's orbital distance.
Ceres is not astroid, it's a dawrf planet.
Distance to Ceres: 491,785,528 kilometers
Distance to moon: 238,000 kilometers
Relative width of beam: ~1,000x at Ceres
Approx width of beam at Ceres: 450,000 km
Ceres is tiny, and far away.
A dinosaur society trying to stop asteroid impacts amazes the inner child part of me
how much resolution is on recieving end?
if we can't raster when sending signals, can't we just raster when it comes back? like normal photo
HO-LY, I love your content. I'm legitimally in awe. I'd hug you if I could
Is this possible to do with sonar? (sound card + GNURadio maybe)
I never got my head around how radio waves of a couple meters could be imaged without using a hell lot of meters long antenna(a couble millions of them for high res images). now i do
1:05 although image sensors like CCDs and CMOSs are composed of discrete sensors that you can call "picture elements" (aka "pixels"), and not only that but CMOS images sensors are actually named "active-pixel sensor" (APS), those "pixels" are not your standard RGB triplets as you'd expect. They use a color filter array, usually a variant called Bayer filter. So despite most sensor devices handing you the fully RGB processed by "demosaicing" the raw data, inside the device what you have is a matrix using some manufacturer specific arrangement. In the case of Bayer filter it consists of 2x2 quadruplets with 1 red sensor, 1 blue and 2 green, but some others have white specific detectors, some use non aligned lines of sensors, and even some others use layered sensors.
So while obviously not as nearly as complex as getting data using the doppler effect, time delay and so on, they also require some computation to get an actual image from the raw data, many performing interpolation as part of the demosaicing process to fill in the gaps.
what happens if the the rotation axis is pointing more or less towards earth, or the astroid is just spinning very slow? Would the doppler effect tell you any usefull information, and could you tell the difference between the two?
Doppler wouldn't get you much, but trying again in 3 month works because the axis of rotation won't point at earth anymore.
the copmuter has been developed after 1980 I am astonished how arecibo was working before that time period with huge data
3:10 Unfortunately the police now use lasers which completely defeats radar detectors unless the laser beam hits the sensor, but by then it is too late.
Surely the Doppler effect of radio waves returning from a slowly tumbling asteroid is impossible to determine? The effect must be so close to zero! What incredibly sophisticated and sensitive technology.
The stealth bomber booping in hot nets an upvote
Wow!
@2:33, I'm a little concerned with how close that asteroid is... :D
So did they used polarization to tell north and south apart?
I read an Arthur C Clarke book - unsure which - that suggested you could explode an atomic bomb in space as a "flash bulb" and then listen for echoes
after the past couple years, i dont think im alone in saying "nah brah, just hit us"
So does the rotation of the earth not cause the light coming back from the asteroid to be slightly shifted? Or because it's light is it just such a short time scale it doesn't really make a difference?
Great question! I wondered this too. I believe that it all washes out since the light is all leaving from earth at the same time so it all gets the same Doppler shift. Later you’re only looking at differences, so a flat sum just falls out.
@@AlphaPhoenixChannel oh I meant more of physically shifted, as in it wouldn't hit the telescope receiver quite right
It's Ponyboy! C. Thomas Howell.
7:38 looks like Ditto on the left.
Technically, isn't it possible to use planetary RADAR on outer-solar-system bodies? It seems like it would just get wildly impractical, but not technically impossible. If you had an object that you knew was very close to half a light-day away, you could blast it with a signal at, say, noon, and then noon tomorrow you point the signal in the same place again, hopefully getting a decent return signal.
Thinking about it, a Moon-based RADAR telescope could circumvent the 1-day (or some integer number of days) restriction on delay by changing the definition of a day. By using a natural Moon crater, you could also get a much larger dish than here on Earth, potentially reducing the losses incurred by sending a RADAR pulse some huge distance. Speaking of, I'd bet that the microwave generators would have to be rated to a few MW at least.
I also wonder what kinds of scientific value RADAR imaging things like TNOs might have. There's also no way this could be scaled up enough to image extra-solar planets with any kind of practicality, right? The losses are distance^4, meaning that if Arecibo was good for 30 lightminutes with 1 MW, to be good for 1 lightyear with the same optics (not factoring in a large dish for convenience), that'd be... 17,520 times as far... about 10^17 times as powerful... about 100 zettawatts... or about a thousandth the output of *the sun* shot in a tight beam at our nearest neighbor. Not only is this impractical, but the stellar neighborhood's homeowner's association would have a riot.
haha I believe Arecibo has a roughly 10 AU limit (from a Scott Manley video)
Hopping on the wolfram to confirm:
2*10 AU / speed of light = 166 minutes
1440 minutes / 360 * 40 = 160 minutes
After 10 AU of there-and-back lightspeed, Arecebo's 40 degree cone passes completely over an object so tracking would fail. Imaging something a light day away sounds really interesting, but you'd need a LOT of integration time because of the r^-4 issue
I also REALLY want to see crater telescopes, but I think that we need a lot of starships flying to the moon to make that happen...
@@AlphaPhoenixChannel Thinking about it, it seems really difficult to escape the fate of needing lots of integration time. Probably easier to escape with a very large dish rather than a very powerful transmitter, as the active power requirements for the latter seems prohibitive.
With a crater telescope, a 40 degree arc translates to about 72 hours maximum tracking time. This would allow for imaging objects in a much wider range of ranges (lol). How alluring a crater telescope is makes me wonder if NASA hasn't kicked around some very hypothetical mission plans for building one. The lowest payload mass requirement option would probably involve sending a few paving robots ahead of time to spend a few years polishing a crater into a dish.
Also, speaking of Starship, how about that 15km hop, hopefully tomorrow? Bets on success and/or type of failure experienced? My bet's on an engine failure upon reignition, resulting in SN8 going ker-splat outside of the launch complex.
Exactly right. With the world's most powerful radio transmitter and the world's most sensitive radio receiver, we could do asteroids and some of the Jupiter and Saturn satellites (Saturn's rings are ice and ice is shiny to radar). So to do something like Europa (Jupiter's shiniest moon) if it were 1 light-day away , you would need a few hundred thousand Arecibos. Not literally impossible, but yes, wildly impractical. It would also cost about a million dollars a second to operate.
Why use Doppler to measure speed for radar guns? Seems like it would be so difficult to try to measure redshift, and easier to just sample distances many times per second and do v=d/t
It is actually really simple to measure the "redshift". You only need to measure the difference in incoming frequency from the outgoing frequency. This can be done by mixing them and you get the frequency difference, often in the audio frequency range. You are basically doing interferomety and get one cycle in the out signal for every half wavelength the object moves. The problem with measuring distances to get velocity is that you will get echos from a lot of stationary objects as well as the moving target. With dopler radar all stationary objects have 0 frequency shift and can easily be disregarded.
Nice airplane reference
I wanted a dinosaur watching a radar thing but once I remembered he actually said pterodactyl I HAD to squeeze that quote in
*boop*
boop
@@AlphaPhoenixChannel boop
Wait, did I miss it, or did you skip how they separate the north and south hemispheres to makes those pictures?
You have to do it again on another day when you are looking from a different direction to get a sort of "stereo" view.
Cool, I also thought raster scan. One point it is not the only preventable natural disaster. Global warming is also preventable and will have catastrophic results if not prevented.
Really good video! I just have one comment... Pronounce the A more like Ah, Ahrecibo, soft a
XD anyway love your content!
why do the reconstructed images look like theres a light source? Like there is lighting information in them
Good question! I glossed over this in the video - Since all of these "pictures" are effectively taken from the rotational pole of the asteroid, the bright side is actually the direction towards earth (the observer). if you roughly assume that an asteroid is a sphere, MOST of the surface presented to earth to reflect radio waves is on the "front" face of the asteroid, so it's always biased to look brighter. In my examples I kinda swept that necessary geometric correction under the rug...
@@AlphaPhoenixChannel Oooh that makes sense. That rim light look intrigued me, i assumed i would look like theres a flashlight from the eye of the spectator.
Thank you
Could they not use some sort of lightweight skin to replace the concrete dish?
The actual reflective surface of the dish is individually-tiltable sheets of aluminum. When your light has a 12cm wavelength, your “mirror” doesn’t need to be real smooth by human standards
Watched this after seeing Don't Look Up and the dinosaurs at the end of this must have inspired the plot of the movie. 😂
RIP Arecibo
ksp SCANSAT users: yeas this is big brain time
As I see you use Resolve a lot, I am not sure if you are using Fusion. But there is two different radar motion graphics examples in the Fusion templates that are meant as a reference. If you haven't looked at them yet - take a look and learn about how Fusion uses a CoordinateSpace node to go to polar. And what issues it has to fix due to the widescreen videos.
Radar is active imaging. But you can still just listen to those wavelengths(/frequency, same thing but used at this end of the spectrum more often) and find emissive targets or other reflections. Visible images are mainly reflective, only very few things are emissive, some are transmissive. The opposite is the thermal infrared. Especially 8-12μm which has an atmospheric window and can be seen using uncooled microbolometers. Which is what I am really interested in.
Go even more extreme in wavelengths and you can do terahertz imaging, which can be done passively and actively (airport scanners).
While at it, try and make sense of radio astronomy interferometry. Which is physics, but magic for the data and results. Allowing you past Dawes limit.
I wonder if this could detect spaceships
Veritasium just made video about this topic. They claimed we cannot do anything about coming impact even when we detect it well ahead.
Do you know actual science about this?
I talk about the DART mission towards the end of the video. There are loads of options on the table that are being designed built and tested. Sending Bruce Willis with a nuke probably won’t work though...
@@AlphaPhoenixChannel They pretty much went through them all and said they don't work. But I guess it depends on asteroid size.
Just finished - he said that none of them work with today’s technology ready to launch, but he said that building the telescopes and cataloging the sky was the necessary first step - that’s all I call for here. Literally the first test deflection is only launching next year - if one is about to hit now, yeah we’re screwed...
DART is also a kinetic impactor, which they didn’t discuss in that video (I’d like to hear a breakdown of the scale of impactor we’d need to alter an orbit of iron and rubble asteroids of different diameters). I’m sure that knowing the composition and spin of an asteroid are even more important for a successful kinetic impactor mission.
The kinetic impactor is basically the “attach a rocket to it” method that he discussed except you store all your energy as velocity over time and then deliver all that energy at once, which brings its own complications.
Edit:autocorrect
@@AlphaPhoenixChannel OK, maybe I got overly negative impression. I guess I was bit too tired to focus. Thanks for the review!
I don't get how the telescope hasn't spun to the other side of the earth by the time the signal comes back
That actually was the limit on the range of Arecibo. They can only tilt like 40 degrees so a best-case alignment they could only ever measure something (24/360*40/2) light-hours away
I'm just here to see if anyone recognised the KZN 'Speed Cop' 😂
Found by a wikimedia search for “radar speed gun” I believe
@@AlphaPhoenixChannel ah OK, it's from KwaZulu-Natal in South Africa, generally don't see much of that stuff outside of South Africa which is why it stood out to me
B O O P
"The red zone is for loading . . "
"Preventable." Ehhhh... That's assuming we see them far enough ahead of time.
Well... yeah I mean that's basically his point. That's why he's saying we should be investing more into satellites to detect these asteroids. Compare that to something like a tornado, where even if you can see it coming ahead of time, there's not much you can actually do to prevent it.
Yeah - they're referred to as "preventable" by people who WANT them to be preventable in the future (including me). If one was just observed and scheduled to impact next year, we'd have nothing ready to go, and there's probably absolutely zilcho we could do, but I'd bet that a HUGE amount of money would magically fall into space research....
boooooop...... boooooopp.....
booop
@@AlphaPhoenixChannel omg i got booop'd back!! 😍
😂
i can now do some math or something and find out the topology of your keyboard or something.
love it! 2:20
Arecibo was condemned! you mean crashed and burned from neglect.!!
How bout some coffee Johnny? No thanks.
looks like a smart, better adjusted Pete Davidson
Just watching this after the arecibo is all fucked up lol
arecibroke :(
What if the telescope was destroyed on purpose because there is an asteroid headed directly for Earth and only a select group of people know and they’ve sabotaged all the facilities that could potentially detect and figure it out? 😳
Sad that it’s gone forever now
boop
_boop_