Flying at extremely low altitudes in the Ukrainian warzone is a standard for both the offensive and
defensive sides of this war. Fly too high and you will most certainly be shot down by a missile. Fly
too low and you would probably make it, although the risk of hitting trees, powerlines or even
a truck means a similar destiny as being hit by a missile. It’s a tough choice, and that’s
why many pilots on both sides refer to their sorties as “suicide missions”.
But flying low is not the same thing as “flying under the radar”. See, during the Cold War, fast
jets could fly below 250 feet and mostly avoid enemy radar scans. “Flying under the radar” is
in fact an antiquated term, stemming from the days when radars tended to look upwards at an angle,
because they were not effective in scanning the terrain horizontally, and so airplanes
could fly below the angle of the radar scan. But that is no longer the case. So … why is it that
Russian and Ukrainian airplanes still fly so low to the ground? We will cover the 4 main reasons
... but how Americans in 1960, mis-identified the moon as a missile threat, is Not What You Think!
The concept behind Radars is quite simple. A transmitter sends out a narrow beamed pulse
of electromagnetic energy. When the beam hits an object that can reflect its energy,
some of the beam echoes back to the Radar, where it is picked up by a receiver,
and after processing, the result is displayed as a “blip” on the radar screen.
Once a target is acquired, the relevant information can be sent
to an anti-air system which can consequently launch missiles.
The pilot may avoid getting hit using countermeasures, but usually the missile wins.
As of November 2022, according to visually confirmed evidence, Ukraine has lost 50 combat
aircraft and 22 helicopters, while Russia has lost 62 aircraft and 55 helicopters.
The best mobile radar system in the Russian military is Nebo-M which performs target
acquisition for the Russian surface-to-air batteries such as S-300, S-400, Pantsir and
others. Under ideal conditions, it can detect targets up to 372 miles away, but in practice,
due to the following four reasons, radar performance can be drastically reduced.
The majority of radars are “line of sight” systems, similar to a flashlight. Just like
the beam of a flashlight cannot go around corners, radars cannot “see” beyond the curvature of the
Earth. The radar needs a clear line of sight to the target, so if something is in the way,
the target does not receive the electromagnetic wave, which means there will be no echo to detect.
But if there is a clear line of sight, radars can see things really far. How far you ask? Let’s just
say that back in 1960, only two days after the “Ballistic Missile Early Warning System” had
become operational in the United States, there was a warning that a missile was coming toward the US.
Although, it soon turned out that it was a false alarm. The radars had mistakenly identified an
object that was 250,000 miles away as a threat! It was the moon rising over the horizon!
Since most mobile radars like the Russian Nebo-M cannot see over the horizon,
their detection range depends on two factors:
the elevation of the radar antenna, and the altitude at which the aircraft is flying.
For example, if the radar’s antenna is 16 feet above ground, and the aircraft is flying at an
altitude of 100 feet, the radar’s horizon range would be 17 miles. But if that same
aircraft flies at 33,000 feet, the radar would be able to detect it from 227 miles away .
This is why setting up radars on elevated ground, like a hill,
would make sense, since it increases the detection range of low flying aircraft.
The downside is that it makes the radar an easy target for a missile strike.
I should mention that radars that can see beyond the horizon also exist, which are called
“Over-The-Horizon” radar systems, but due to their large size, they are stationary structures.
This makes them less relevant to the war on the battlefield,
since they do not communicate with anti-air batteries on the ground. At least not yet.
The second factor is terrain. Whether it's a valley or a hill, both can physically mask the
aircraft from radars. Getting below a treeline or building can also do the trick. In fact,
back in April of 2022, the Ukrainian Air Force successfully utilized the terrain to their
advantage, when they re-supplied and evacuated wounded soldiers from Azovstal in Mariupol,
the city that was completely encircled by Russians. Ukrainian helicopters leveraged
the terrain to avoid radar detection. Although after conducting a few of these missions, Russians
caught on and relocated their radars which allowed them to destroy several Ukrainian helicopters.
Kyiv was left with no choice, but to stop those helicopter runs.
The third is radar clutter, which can be in the form of atmospheric crud or ground clutter.
Anything in the atmosphere, be it rain, smoke, dust, clouds, birds and even
water vapor can bend, scatter or absorb the electromagnetic transmissions from radars.
This can in turn dramatically reduce the effective range of the radar and
further complicate the detection of aircraft against the noise. The farther the target is
from the radar antenna, the bigger is the problem with the atmospheric crud.
Then there is ground clutter, a phenomenon where trees, buildings,
power lines and other objects on the ground reflect back the radar signal.
This can make it quite difficult for radars, whether they are on a ground, or in the air,
to differentiate between a low flying aircraft and all the “noise” bouncing back from the ground.
Although the modern “doppler” and “look down/shoot down” radars have, for the most part,
resolved this issue. Modern radars are able to filter out fixed targets and focus on moving
targets … and yet, it’s still possible for low flying aircraft to get lost in the clutter.
This is referred to as “Nap-of-the-earth” flight, where a helicopter or fixed-wing
aircraft flies at extremely low altitude to blend in with the ground clutter,
effectively blocking the line of sight from ground-based and airborne radars.
During the “nap-of-the-earth” flights, helicopters can fly as low as 10 feet above the ground,
but jets only fly as low as 50 feet off the ground, due to their much higher speed.
Once the aircraft approaches its target, it pops up to attack, and then turns back before
the enemy can even respond, a tactic that is utilized by both Ukrainian and Russian pilots.
Flying over roads and highways can further help to blend in with moving vehicles,
especially for helicopters which can fly lower and slower. While theoretically,
airborne radars could likely detect a low flying aircraft over roads, in reality, deploying such
valuable assets on a daily basis near a warzone would be too risky for Russia or anyone else.
But wouldn’t a low-flying aircraft be an easy target for MANPADS? It would, but only if you can
see the aircraft. A low flying aircraft that moves at high speeds doesn’t give MANPADS operators
much of a reaction time. It would appear and disappear over the horizon in a mere few seconds.
That said, fly too high and too slow, and you’d be the perfect target for MANPADS.
The fourth reason why aircraft fly extremely low in warzones, is to take advantage of multipath
interference. Even if the radar signal bounces off of the aircraft, the returning signal could
reach the receiving antenna via two or more paths. This is because the returning signal
could bounce off the ground, bodies of water or any other object on its way back.
When the same signal is received over more than one path, it can create ghost targets
which appear and behave the same way as the actual target, making it more difficult for
radar operators to figure out which “blip” on the radar screen is the real target.
For example, the radar could see 3 moving blips at 3 different elevations,
one of which is the real target. This reduced the chances of the airplane being shot down.
Early on, we established that flying high in a warzone is a suicide mission,
since long-range radars can easily identify the target and anti-air missile systems, like S-300,
can shoot it down from 90 miles away. But this doesn’t mean that flying extremely close to the
ground is without its own risks. The obstacles on the ground, anything from trees to powerlines,
can pose a serious threat, especially that things like power lines are not so easy to spot.
Sometimes special maps are produced that plot the routes of these power lines, but their accuracy is
questionable, especially when it's in a foreign country. For this reason “nap-of-the-earth”
flights are mostly conducted during daytime, when visibility is high. Although they do happen at
night too, with the help of the night vision goggles. While the exact number of crashes
related to flying low is unknown, they have happened to both Ukrainian and Russian pilots.