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
A big part of it is signal to noise ratio. If the radar return is really low then it will blend in with the all the other radar noise that the system picks up. https://www.youtube.com/watch?v=hwX5oc9yv4M does a good job of explaining the detection problem.
Radar detection is subject to uncertainty. The more you tune to focus on velocity the less certain you can be of position, and vice versa. So, narrowing position to “bee-size” would make it difficult to distinguish between a fast or slow bee.
Asking a radar to look for a fast bumblebee is like asking a person to find a moving white dot in a bunch of TV static. It is incredibly difficult to identify anything out when there’s a ton of signals and noise constantly appearing and disappearing at the same intensity as the thing you’re looking for, much less figure out how fast that thing is going.
Partial and incomplete answer, but at an ELI5 level – it’s really hard to tell if that bumblebee is moving really fast, or if you’re just seeing different bumblebees.
The spectrum of your radar has a certain energy before you turn the beam on, this is called the noise floor. You can’t make that go away, it’s caused by the Sun and all the electronic technology in use.
To see the stealth airplane you need a return from the airplane that you can detect, it has to be about twice the noise floor. Modern stealth shapes reflect away so much energy (that’s why they have those fun-house mirror shapes) that you have to pump a dangerous amount energy out to get a return 2X the noise floor. Alas, when there is more than one radar, your super powerful radar raises the noise floor in all the air you shine your beam into. It’s a diminishing returns problem. Eventually you’ve got a beam that drops birds out of the sky wherever it points, and stealthy planes are still stealthy.
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