Recently, Qilu Satellite issued an article through its official account [Come but not go, it is disrespectful], saying that the Qilu Satellite 1 took time-series photos of the Nimitz-class aircraft carrier docked in Norfolk Port, the United States. "The seams on the aircraft carrier deck Details are clearly visible”. This is a response to the fact that the new aircraft carrier "Fujian Ship" was followed and photographed by the US MAXAR satellite after it was launched.
![Recently, Qilu Satellite issued an article through its official account [Come but not go, it is disrespectful], saying that the Qilu Satellite 1 took time-series photos of the Nimitz-class aircraft carrier docked in Norfolk Port, the United States,](https://cdn-dd.lujuba.top/img/loading.gif)
The lower right is the Qilu-1 satellite imaging the US aircraft carrier
A friend saw the image and said, is the Qilu satellite bragging? The image is black and white and blurry. How can it be compared with other high-definition large pictures?
On most satellite maps, we can often see high-definition aircraft carrier images. Take these two aircraft carriers in the Port of Norfolk, USA. One of them, the CVN69 "Eisenhower", looks like this after zooming in:
CVN69 Aircraft Carrier" "Eisenhower"
Although the deck welds are not visible, the four arresting cables in the landing area are clearly visible, indicating that the resolution of the image has reached centimeter level.
Looking at the satellite photos taken by Qilu-1 , we can distinguish the four catapults and flame deflectors of the aircraft carrier, but we cannot see the arresting cables clearly, let alone the "seam details". Perhaps Qilu Satellite released it on the public account is a low resolution image only and is not its highest resolution version.
Part of the Qilu-1 imaging of the US aircraft carrier
Here we are going to talk about what radar imaging is and what the real capabilities of the Qilu-1 satellite are.
Unlike most earth observation satellites , the Qilu-1 satellite is a synthetic aperture radar (SAR) imaging satellite. This satellite does not use our traditional cameras or other optical components to take photos. It relies on radar Antenna emits and receives electromagnetic waves , and then generates images after computer processing.
Radar produces imaging by emitting and receiving electromagnetic waves
It is said that "seeing is believing" and "a picture is worth a thousand words". Nowadays, optical technology is so advanced that even mobile phone cameras can "photograph the moon", Hubble Telescope can Stars millions of light-years away are photographed, and some people say that intelligence satellites can even distinguish the license plates of cars on the ground. What is the use of radar satellites?
This is because radar satellites have "stunt skills" and can take "photos" that ordinary optical satellites cannot.
We cannot see the scene in front of us clearly in the dark night, and it is difficult to take clear images with mobile phones, because the lens, like the eyes, relies on the reflected light of objects to form images. Radar does not need to rely on external light. It can emit electromagnetic waves to the target itself and receive electromagnetic waves scattered back from the target through active remote sensors.
The satellite emits electromagnetic wave pulses to the ground through radar
The radar imaging satellite is like having a "searchlight". It can not only take pictures during the day, but also take pictures of the ground at night when you can't see your fingers. This is it It is more powerful than optical imaging satellites.
Most visible light cannot penetrate clouds and fog, so when the target area is cloudy, rainy or has severe haze, optical satellites become blind. Radar imaging satellites are not affected by clouds and fog because the radar waves they emit can easily penetrate clouds without being absorbed or scattered. Whether it is dense clouds or heavy rain, they are transparent to radar satellites.
Depending on the wavelength of the radar waves, some satellites can even penetrate vegetation and the ground surface to see clearly what is hidden in the woods and underground. You may be able to hide it from detection by optical satellites by piling branches on the tank, but to radar satellites, you will be running naked.
The difference between optical imaging satellites and radar imaging satellites
Visibility does not mean seeing clearly. The imaging resolution of radar imaging satellites is also related to the size and sensitivity of its antenna. We cannot make the satellite antenna very large. At the same time, radar satellites usually fly in orbits 500 to 800 kilometers above the ground, which is higher than the altitude of many optical remote sensing satellites. Logically speaking, its imaging clarity is not as good as that of optical satellites. .But in fact, some radar satellites can already distinguish millimeter-level objects on the ground. This is mainly because they use synthetic aperture radar technology and advanced algorithms.
Principle of synthetic aperture radar
The satellite flies around the earth at a speed of about 7.6 kilometers/second. When it receives the signal reflected back from the previously launched radar beam, it has moved forward for a certain distance; and for the same satellite on the ground Target, the satellite will receive many reflected signals at different locations in the sky, which is equivalent to expanding the area of the satellite antenna many times. Each "picture" of these reflected signals looks like a screen full of snowflakes, but when these signals are fed into a computer for calculation, a very clear image can be generated. Of course, since the satellite transmits and receives microwave signals, which do not contain any "color" information, the final image it generates is also black and white, and we cannot distinguish the color of the object from it.
Radar satellite images are all calculated from "snowflake points"
China's Qilu-1 satellite constellation is a synthetic aperture radar imaging satellite. As a commercial low-cost small satellite, the Qilu satellite weighs only about 150 kilograms and can easily weigh several tons. Compared with the more than ten tons of military satellite , it is just like a toy, but it works in the high-frequency Ku band, and the image resolution it captures has reached centimeter level, and it can distinguish the iron towers and wires on the ground at an altitude of 500 kilometers.
The SAR satellite can distinguish the wires on the ground
According to public information, the Qilu-1 satellite also uses interference imaging technology, so it is a more advanced "Interference Synthetic Aperture Radar" (InSAR) satellite. Through the networking of space routers and laser communicators with other Qilu satellites, many applications such as rapid revisiting of ground targets, multi-station, interference, tomography , holographic , etc. can be realized. Not only will the images acquired be clearer, but also Capture complex elements—including position, distance, speed, and direction of movement—to accurately measure target changes.
Because metal objects have a strong reflection effect on electromagnetic waves, cars, airplanes, ships, etc. will be "seen more clearly" by synthetic aperture radar satellites. In InSAR satellite images, you can even distinguish ground building ceilings asbestos tiles of fixing screws.
CVN75 "USS Truman" aircraft carrier deck
The deck of another aircraft carrier CVN75 "USS Truman" docked in Norfolk Port is not as flat as everyone thinks. It has many "patches", welds and fixations on itCarrier-based aircraft These things can scatter electromagnetic waves more strongly, making them easier to be imaged by radar satellites. It is not unreasonable for Qilu Satellite officials to claim that "the details of the seams are clearly visible."
In contrast, non-metallic objects such as people and trees appear slightly blurry and are not so easy to be photographed.
Satellite radar can image through clouds and darkness
The aerospace technology of the United States is world-class. They have a huge number of various reconnaissance satellites, but our satellite technology is not bad either.
"Qilu-1" is a small civilian satellite. It can observe the Earth all day and all day, and can also perform high-precision imaging of vehicles hidden in the woods and ships on the sea. The clarity of its shots It can "distinguish the seams on the aircraft carrier", and no monsters or monsters can escape its fiery eyes!
#Qilu-1 satellite can photograph the seams of the US aircraft carrier#
