I know human Gliders were used recently against Israel. I’ve also seen reports of Russian glider bombs successfully targeting Ukraine.
Are Gliders basically invisible to modern Air Defense Systems?
Are sentries using binoculars the best defense?
How can gliders be detected at night?
Gliders would be visible to radar the same as any other airframe of similar size.
Wouldn’t the low altitude make a difference?
I don’t know if that’s a movie trope or real science.
Only at long distance. A ground-based air defense radar can see as far as its horizon, but that horizon includes low-altitude airspace close to the radar. And a ground-based radar on high ground has a formidable horizon distance.
There’s nothing magic about low altitude. It’s simply a matter of allowing terrain to block the radar’s line of sight. If the radar has some height, that’s harder to do.
Besides, gliders are capable of some very high altitudes.
Thank you.
I learned something new today. 
You’ve left out the most important qualification: and made of the same material. The materials gliders are typically made of are far less reflective of radar waves than typical aircraft airframes.
The radar horizon to an object flying at very low altitude is incredibly small compared to the horizon of an object flying at a high altitude.
Using HORCALC - Page of the Radar Horizon Calculator (mar-it.de), for a radar with an antenna height of 10m with the target’s height also being at 10m, the radar horizon is only 26.12km. Using a radar antenna at the same height but with the target flying at 10,000m, or roughly typical airliner cruising altitude, the radar horizon is 426.056km.
ETA: The radar horizon is a result of the curvature of the earth physically being between the radar and the target. The same as there is a visible horizon past which you can’t see an object at a set altitude regardless of magnification because of the curvature of the earth, there is a horizon past which an object at a given altitude can’t be seen by a radar, regardless of how powerful it is.
As noted, they can be seen on radar to the same extent as any other aircraft constructed of similar materials. To the extent low-flying aircraft may be harder to detect at range than higher altitude aircraft, I should think that’s actually a huge disadvantage for a glider: a glider, not having an engine, can hardly be expected to maintain a low-altitude flight profile for long. Gliders have to trade altitude for distance: less altitude means less distance.
Plus, you have to consider the aircraft launching the glider: even if the glider itself might have certain advantages over a powered aircraft, it still has to be launched from something, and close enough to whatever objective to allow the glider to make it there from whatever altitude it is launched at (and, again, the higher the starting altitude, the longer the distance, but the easier to detect—both for the glider and for the launching aircraft).
Some of the gliders used in the Ukraine War are literally made out of cardboard. They’re not much different from toys, aside from their payload.
Then the trick is simply to kill the archer (as the saying goes).
Also, the Palestinians used powered parachutes, essentially. The chassis. prop and engine would still have a radar signature. However, if they are low and slow enough they might be filtered out by the radar’s software.
It occurred to me that the word glider is causing confusion in this context, in neither of these cases are these ‘gliders’ of the of the kind that one would typically think of when visualizing a ‘glider’; I did the same in my first reply. The ones used by Hamas were paragliders, open aired carriages powered by a fan at the back and with the lift provided by a shaped parachute it is attached to.
It has the radar cross-section of a person or two sitting in a very lightweight metal frame just big enough to sit the one or two people, the fan on the back and an attached parachute, i.e., not very much.
Glide bombs are just bombs with fins attached to them to allow the bomb to glide, they have the radar cross-section of well, a bomb with fins attached to it, i.e., not very much. They’ve come back into fashion with the war in Ukraine as both sides are in extreme danger of surface to air missiles if they fly over hostile territory, or even their own territory that is within range of SAMs. It’s not a new concept though, only the need to deliver them by climbing to pitch bomb them from the safety of one’s own airspace while minimizing exposure to air defenses to avoid such extremely dangerous airspace at higher altitudes is. This is a German Fritz-X radio-controlled glide bomb from WWII.
Gliders can be launched using ground based tow vehicles. The only time I was ever in a glider it was launched using a truck with some type of fast winch. The truck was stationary, and the winch pulled us to 50MPH (or whatever), at which point we went up into the air, and dropped the tow cable.
I’ve not heard anything to suggest Hamas was using a setup like that, just making the point a tow plane is not necessary.
Exactly, this is the crucial point - every picture or video I’ve seen showed a frame with a fan in the back, chute overhead. They can vary the materials a la the Brit ww2 Mosquito fighter which was balsa wood, but wouldn’t radars a) be sensitive enough to pick up the fan which is unlikely to me non-metallic and b) see a cluster of small blips, and the radar operator notice something is up even if he can’t ID them as paragliders? It’s looking a lot like lack of manpower due to a holiday that day, huge Intelligence failure, & possible radar failure either the machinery, software, or liveware supposed to be looking at the scope.
I recall an article when fibreglas homebuilts first became popular, that these aircraft were relatively invisible to radar, at least the ones usually used to monitor air traffic. The engine alone (a 100hp size or so) did not have a big enough cross-section. A recommendation was to use a lead-based paint to ensure a decent profile. The article also mentioned an aircraft spotted visually by the Coast Guard, but not on radar, that was being used to transport drugs from the Bahamas to Florida.
Many fixed-wing gliders nowadays are fibreglas too. But then, that’s not the sort of thing we’re talking about, it’s the powered paraglider. The cloth sail is not going to have a radar cross section unless it has an interesting dye, so the question is - can the radar pick up the engine? I would hope in a militarily sensitive area like that, they use radar that can detect things like paragliders and drones big enough to carry a serious payload, not just full-size commercial aircraft. After all, the range is not an issue, the whole strip is 7 miles across at most.