I decided not to really touch on that in depth because 1. I don't fully understand it myself and 2. it could have made this even longer, when I was trying to stick to a high level introduction I do suggest you check out Thomas Ager's book though if you want more in depth information!
Great explanation in the first half. But in the beginning the range is is just one pulse or bump. There is not any explanation, how the one pulse is suddenly many bumps i.e. pixels i.e. picture elements? This is not explained in other vbloggers presentations, so you are not the only. Also the sending perpendicularly is essential to present.
My company built the Worldview 1 & 2 satellites for Digital Globe. I personally helped build the 2-Axis Gimbals for the High Gain Antennas so they could track ground stations even while imaging. We also likely developed GEO Imaging satellites that can image under 1 meter on the surface FROM GEO ORBIT! Ask any Optical Engineer today if this is possible, and they will likely say NO. Lookup the MOIRE Program from Ball Aerospace. (Membrane Optic Imager Real-Time Exploitation (MOIRE) telescope.) It was going to be the next greatest thing in space imaging tech. We built a tech demonstrator of the concept and proved it WOULD WORK. Then the entire program completely disappeared never to be heard from again. I WONDER WHY?
I also helped build the NPP-Suomi Spacecraft which took the images used in the famous "Blue Marble" composite image released by NASA (Bob Simmons) in about 2012. That full earth image was assembled by images from the VIIRS Instrument in LEO. I then helped build, launch, and commission its big Brother JPSS-1 (now NOAA-20). And regarding "imaging technology", I also helped build JWST, Kepler Space Telescope, IXPE Xray Telescope, and I am helping with the upcoming NEO-S mission. My company built the corrective optics for Hubble and now most of the instruments aboard Hubble were provided by us.
Hey, I'm learning SAR and this really helped. I think the only thing I'm still curious to get an intuition for is how they used SAR on film and lenses to do the "analog" computing of SAR images before computers had enough storage and compute to do what they do now.
Muito obrigado por esta aula. Realmente, é contra intuitivo trabalhar com imagem de radar quando você trabalha com imagens ópticas há muito tempo. Parabéns a todos da sua equipe.
Incredible video! 👏 I’m working on looking for a job in the space sector and SAR is something I’ve become fascinated by. I’ve read up on it a bit and started reading Thomas Ager’s “The Essentials of SAR.” Having explanations with visuals like this really helped to reinforce and unlock that knowledge. Thank you!
Strictly speaking, the aperture of a lens is the ratio between the lens opening and the focal length, instead of it being the size of a lens. The smaller the ratio between focal length and aperture (f number), the closer the two are together and the more light can hit the sensor. Numbers below f/1 mean, that the aperture opening is larger than the focal length. Going back to SAR, you can imagine that by moving the radar satellite around while looking at the same object is similar to opening the aperture of a lens (like going from f/11 to f/1.8 in the image at 9:30) more and more and letting more light in and thus increasing the Signal to Noise Ratio. With digital cameras, this means we get more detail and less noise and with SAR it means... the very same thing :D
Totally! I didn't do the best job of going from f/1 in optical -> SAR I also wanted to mostly convey the idea of why it's called "Synthetic Aperture" in a relatively short amount of time. That's why I like the fact people can comment on these videos, I get new ideas as to how to better tell these next time :)
Personally, I'd explain SNR with sound. Let's say you have two speakers: one plays, let's say, an audiobook, and does so at a set volume that you never change. The second speaker plays white noise. Speaker #1 is your signal, speaker #2 is your noise. As speaker #2 gets louder, it's more and more difficult to understand the audiobook and at some point the signal is unusable because of the very high noise.
Oh my, good catch... That's starting to be a lot of typos for a 23min video. I spent a lot of time trying to get the basics right, that I seem to have overlooked some of the polish here, apologies for that I'll try to do better next time!
I'll be posting your video on the NasaSpaceFlight forum to give you a greater audience and possibility of a 3D Bender editor with the skills your searching for. Best, Tony. (also i"m you 901st subscriber)
Really great explanation Maxime! The most comprehensive (and entertaining) video on the subject of SAR. This should be essential viewing for anyone getting into Earth Observation.
SAR can see into buildings the same way when you bounce a ball under a table and strike the underside of the table, the ball bounces back to where it was thrown, never through the table. If a building has an opening wide enough the microwaves can bounce back out the opening and return an image of what was inside. Think like a jet in a hangar.
That's true! Different wave lengths also have different penetration properties, so some can go through very thin roofs to see below, there are some examples of seeing planes through hangars in SAR. I made the choice of not talking about different bands to keep it short. And that Capella blog post just makes me laugh
Turns out you can't add a link at the end of a video with less than 1k subscribers :') So please subscribe, and here's the Patreon link. Not as fun as clicking on my face but it would help just as much! www.patreon.com/mindsbehindmaps Also, some mistakes spotted by viewers: - All the early animations explaining the basics of radar have a typo in them: It's "Received Energy", not "Recieved". This one's painful because it appears so many times - 7:43 has another typo, "Synthetic" Aperture Radar. Thanks to everyone for keeping me accountable and pointing these errors out!
Great video and great timing as I'm writing up my dissertation, subscribed! One note though: in the "Basics of Radar" section it should be "receive" and not "recieve."
@@MaxLenormand I saw that too, and I think it makes it even better. It shows you did the figures. It is the imperfections that bring the sense of scale of the effort :)
I still couldn't find the info I was looking for. From what I saw a satellite takes at most two hours to circle the Earth. This means it covers 2,77 meters in 1/2000 of a second. So if that's the speed of the camera shutter, it's a 2,77 meters blur. Is there a motor on the camera to make it track the surface of the Earth, cancelling the satellite's speed, or is the shutter speed faster?
That's a good question, I'm not quite sure! A quick search found this Quora question with someone mentioning Corona spy satellites would rotate to compensate: www.quora.com/How-does-satellite-imaging-work-If-satellites-are-moving-really-fast-how-do-they-take-photos-of-specific-places-without-any-motion-blur
Content and quality on a very high level! I was very surprised that you have only one video and less than a K subs. Continue your work! You have a very high potential and skills that will pay off!
RU-vid removed ability to link in Shorts. Yay. See the latest community post I made to find the link If for whatever reason you're on desktop, here's the link: forms.gle/8d9ekNxTi1FVYdyp7
There are Geostationary satellites above us as well. The name suggests they are stationery above a certain location or area - sync orbit. Enter real time observations. Thanks for a great video.
I wish you had explained you had explained the relationship between the diameter of an objective lens and the maximum resolution of the system. The Dawes limit.
Regarding being able to notice millimeter differences; Since the U.S has treaties limiting the number of ICBMs, we have more launch sites, than we have missiles. So missiles are shuffled from one site to another to keep their exact location unknown. The trucks that move these missiles, have suspension systems that will lower the trucks to look like they have a heavy missile on board, when they are actually moving an empty shell. This fake "squatting" is done to fool the satellites that can notice the difference. The ultimate shell game.
