I was watching a youtube video about the b2 this morning. It mentions that while it’s not completely invisible to radar, it only has a cross section about the size of a bee. It says that radars have to fine tune their displays to only show larger objects or else it would be too cluttered.
I guess my question is, why can’t they tune their displays to only show objects moving faster than ~ 300 mph?
In: Physics
[Here’s the video](https://youtu.be/flwgwIRo_lk?si=xPi0_KmW0rhA4mV6&t=150) if that’s allowed.
Think about radar vs low observable aircraft (aka stealth) like this.
A radar is your eyes looking around the sky. If you want to look far or at a large portion of sky, you have to look all around and squint and you don’t get a lot of time to specifically focus on any single point. In that case, since you have a lot of sky to cover and you’re looking far, things that are pretty small are easy to miss, but you’ll see stuff that is bigger or reflective quite easy, even really far away. But instead if you want to just focus on a specific area or focus on stuff really close to you, you can train your eyes on it and focus really carefully there, and just look there the whole time, non-stop, and fast, so you don’t miss anything. These are essentially two different ways to operate a standard radar. A Low frequency, long distance, worse detection, or a high frequency, but shorter distance but much better detection
In the big sky look around, it can be very hard to see a low observable aircraft, its small and you’re not getting a lot of detail until its very very close, but if you focus in one area and concentrate there, you can probably make it out, at a bit longer distance, but still close.
However, there are almost certainly a myriad of other ways to defeat stealth/low observable technologies that are behind the curtain of secrecy.
It’s not just about tuning, which you can do, but for the radar screen to show a return, the radar waves need to return.
Many stealth planes work by absorbing radar waves or reflecting them in a direction other from their origin points.
Yeah, they can and do. MTI filtering and Pulse Doppler are the main technologies. Keep in mind they work based on relative velocity of the radar and target, which is less than the absolute velocity unless the target is flying directly at the radar.
There’s also a pretty big difference between “I think there might be an aircraft in that direction” and having precise enough range, altitude, and azimuth data on the target to actually do anything about it.
So at 300 miles can you see a bumblebee with your eyes?
I’m going to guess no, as I have not seen any scientific paper on your inhuman eyes. In the same way a practical radar can not get a strong enough reflection off of a object of that size at any sort of long range. A bumblebee going 300mph will instantly get flagged by something like patriot, but it can’t see something that small at anything above close range. Like probably inside AGM-88 HARM range.
The sort of radars that can are **huge** like literally thousands of sq. feet, and require there own dedicated power plant that puts out enough electricity to power a small city. This means that such radars are not movable, ridiculously expensive and can be seen by satellites.
This is what one of them looks like. Notice the cherry picker for scale.
https://en.wikipedia.org/wiki/PAVE_PAWS#/media/File:PAVE_PAWS_Radar_Clear_AFS_Alaska.jpg
Here is a “mobile” version
https://en.wikipedia.org/wiki/Sea-based_X-band_Radar#/media/File:US_Navy_060109-N-3019M-012_The_heavy_lift_vessel_MV_Blue_Marlin_enters_Pearl_Harbor,_Hawaii_with_the_Sea_Based_X-Band_Radar_(SBX)_aboard.jpg
As such you can only cover limited areas with these and only protect critical targets. The enemy will also always know where these are so they can easily avoid them, and if they are even sort of close to the front line they will be targeted and destroyed.
You might be able to know that a stealth aircraft is *there* with this method, but you can’t necessarily get a *lock* – pointing a beam at something the size of a bumblebee moving hundreds of miles an hour is real hard, to massively oversimplify.
Also a lot of radars work on people physically watching a screen – you want to show everything with *any* kind of reflection, birds, clouds, bits of cold air and all, and spot the one tiny thing going in a suspicious direction very fast? Not every radar can do that automatically. Sure, the ones that can’t are *old as balls*, but have you seen the age of the gear most units are using in Ukraine?
Radars work by blasting out a radio pulse at a specific frequency that then bounces off of something and comes back. The radar knows when it sent the pulse, and knows when it heard the much much fainter return, and then calculates a relative location based off the time of travel of the pulse, and the angle it was looking.
Stealth or low observable is all about minimizing the radar returns. They do it through a lot of very technical and secret means but it basically boils down to shaping the aircraft to either scatter, absorb or redirect radar return energy away from the radar that is looking for it.
Different radars work at different frequencies based on what they are trying to do. Low frequency radars with huge wavelengths go very far and can see things coming from a very long way away but they don’t have as much resolution and they can’t get very precise locations. These are early warning radars because they alert the military that someone is coming. but it’s ambiguous what that thing is.
sam radars and fighter radars operate in higher frequencies with smaller wavelengths that can see very accurately but not nearly as far and give a precise enough quality track to guide a weapon.
stealth (more accurately Low Observable) technology necessarily has to be optimized against a specific frequency ranges based on what its trying to evade. different wavelengths of the pulses mean they will bounce off different parts of the aircraft, so although a B2 or F-22 will be stealthy across all spectrums it will be much stealthier in one specific spectrum. how it is designed is mostly based on the mission its expected to do and the threat it is expected to face. generally LO is more focused against the radars that can guide weapons because if they cant shoot you it doesn’t really matter if they detect you far out.
LO is designed to make sure that as much if the return as possible will not
bounce back at the radar. and the tiny amount that gets through will fall below the noise floor below which then radar cant see it. a doppler filter to see anything above 300 knots could work but now you have blinded the radar to anything slower and it is still going to be blinded by all the other much louder returns of other airspace users. its kinda like trying to see the light of a match when you have the sun right behind it. because of how faint the return is the aircraft would have to get very close before the radar could see it, effectively shortening the radar range.
also… i can make my relative closure shrink by not flying straight at the radar. i could be going 400 knots but if its at an angle to you your doppler radar would show much lower closure and id fall through the detection floor.
Short answer: noise.
With sensitivity so high to receive reflection from a bumblebee at such distances you will get a huge amount of noise, so a huge amount of fake targets, moving in random ways, appearing and disappearing. Filtering out the real target is difficult if not impossible.
Imagine old school TV’s black and white noise. Now I tell you there’s a “real” black dot moving somewhere in there, try to find it.
Because there’s unavoidable background noise that the signal gets lost in.
Imagine trying to hear bees at a great distance. Even if you perfectly trained your hearing, a bee far enough off would be impossible to distinguish from the sounds of wind, blood moving in your ears, other objects, etc. Same thing with radar.
Modern radar is often working at the limits of signal/noise ratio. Stealth doesn’t make things invisible, it just reduces the range the radar can pick it out of the noise. Same (very) general idea as painting ships have grey so they blend into the horizon.
You also want to think about how a system can be intentionally circumvented once you know its detection thresholds. If you’re looking for 300+ mph bees, well, people will make tiny rockets that look like 300+ mph bees for like $5k a pop and fly them around just to stress you out, until you turn the sensitivity down. Being able to engineer false-alarms is one of the best ways to protect your real intentions.
This is used often in cyber security, to saturate systems or operators with alerts to the point that it’s unmanageable and the detection has to be dialed back.
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