Siheyuan: I eat melons while doing scientific research

Chapter 1406 Sorry, I couldn't resist (5k)

Gao Zhendong was a little surprised: "I remember your chief engineer saying that you are also working on synthetic aperture technology."

"We are working on it, but not many technical details have been released. Not to mention the technical details, even the principles are vague. We only understand a small part of it, so it will be difficult to move forward."

Gao Zhendong was well-prepared for this. He had already searched for information on synthetic aperture radar when he made an appointment with the chief engineer of the radar institute to exchange ideas. Overall, the information was not expensive.

This is the main reason why Gao Zhendong wasn't in a hurry even though he had been waiting for the other party to arrive for a long time. He needed to take the time to digest the knowledge of synthetic aperture radar, and this thing is not so simple.

However, Gao Zhendong is still willing to spend time on this, since synthetic aperture radar has many uses beyond just anti-submarine warfare; it can be used for reconnaissance, land and resources surveys, disaster assessment, agriculture and forestry, and more.

Moreover, compared to visible light and other methods, synthetic aperture radar has an advantage in that it is basically unaffected by clouds and fog, making it far more adaptable and usable than the visible light band.

Moreover, this thing can also perform 3D imaging. Although visible light can also do it, at this point in time, visible light 3D imaging is incomparable to SAR.

"Hmm... what stage have you reached now?" Gao Zhendong pondered for a moment and asked Meng Gong and the others.

Meng Gong was taken aback for a moment, then smiled wryly: "Committee Member Gao, you're flattering us too much. We're not talking about what level we've reached, but rather what level we've learned. To be honest, we still have a long way to go before we can truly start doing anything."

Gao Zhendong was taken aback; this comrade was truly honest.

He couldn't help but laugh and said, "Hmm... alright, so how far have you all progressed?"

"The basic principle has been roughly figured out. It involves combining the speed and direction of the aircraft's flight with the pulse transmission frequency of the radar to generate multiple echoes to a single target unit. These echo data are then used for time-domain and frequency-domain analysis to synthesize signals, increase the aperture, and improve resolution."

“Yes, you’ve grasped the essence of the problem. And then…” Gao Zhendong nodded. The most basic principle of synthetic aperture is not that complicated to understand. Moreover, it is obvious that the other party has indeed grasped this basic principle. You can tell from his words “pulse emission frequency” instead of “pulse frequency”.

Adding the word "launch" makes a difference in meaning.

The former refers to the number of pulses emitted per second, while the latter refers to the electromagnetic wave frequency of the pulse. The fact that Meng and his team can distinguish between the two in the simplest terms shows that they have put in a lot of effort.

Therefore, Gao Zhendong said that the comrades had grasped the essence.

"And then, that was it..." Meng Gong said with a wry smile.

Gao Zhendong was stunned. That's it?

"More specific?"

"We haven't gone into specifics yet; we haven't been researching this area for very long. Chief Engineer Gao, as you know, before you proposed the pulse PD radar, we were still copying old radars in the air with detection ranges that were even less than the human eye. On the ground, we were also copying the previous generation products provided by our comrades in the north. It was only because of the success of the pulse PD radar that we were able to spare the time and manpower to conduct research on imaging radar."

Saying it's inferior to human eyesight is a bit of an exaggeration, since not everyone has such good eyesight, but saying it's inferior to the eyesight of some people with outstanding vision is not a lie.

Meng was not flattering Gao Zhendong by saying this, but rather stating a fact—we have only really started to conduct some research on high-performance radar and special radar in the last year or two.

"In this process, we initially followed the approach of real aperture imaging, which wasted a lot of time. So far, we haven't spent much time on synthesizing apertures, and there are very few details provided in relevant foreign materials."

Confirming that real aperture imaging is a dead end takes time, which is why it's often said that being able to quickly determine that a path is blocked is already a major advancement in the research process.

Gao Zhendong recalled a famous line he often heard in his past life: "Crying? Crying is also a form of time," which was truly a vivid description.

Given the limited time and available information, it's normal that we can only get to this point for now.

Gao Zhendong nodded. No wonder their chief engineer said it was quite difficult.

"Well, how about this? Let me share my understanding of synthetic aperture radar. It may not be entirely correct, but let's exchange ideas." At this point, Gao Zhendong had no choice but to proceed directly.

His words put Meng and his team at ease; they knew they were unlikely to leave empty-handed this time.

Before this, they were still somewhat unsure. Communication can also be considered communication if the other party only listens without speaking, but this is rare with Committee Member Gao. However, rare doesn't mean nonexistent; after all, this technology is relatively new, and it's possible that Committee Member Gao simply wanted to hear from professionals about the latest developments to broaden his own thinking. In that case, to reap any benefits, they would have to wait until he had his own research results.

The fact that Committee Member Gao said he has an understanding of SAR means one thing—he really has ideas.

Moreover, this idea is likely to be more profound than our own understanding. This is not an underestimation of ourselves, but rather because Committee Member Gao's capabilities in radar are a well-established fact.

The three comrades opened their notebooks, which they had prepared beforehand, and listened attentively. One of them had a notebook that was several sizes larger than the other two. His main task was to draw diagrams and trace back the diagrams that Committee Member Gao had drawn during the guidance process as accurately as possible.

It is a true artificial intelligence scanner.

This is much better than taking a photo. These days, those who know how to take photos understand the difference. Besides, this is a place where ordinary cameras simply can't get in.

"Committee Member Gao, please enlighten me."

Gao Zhendong laughed and said, "We're all beginners, so let's just exchange ideas and share what we have."

He's absolutely right. They're all beginners, but he's just in a better position and can learn more and faster.

Engineer Meng was somewhat amused and exasperated. "Yes, yes, you're absolutely right. You're responsible for what's available, and we're responsible for what's not. It's a clear division of labor."

Gao Zhendong's first words made him realize that his joke about the division of labor was probably true.

"In reality, synthetic aperture radar only solves the high-resolution problem in one direction, while high resolution in the other direction is achieved through other means..."

This first sentence hit the comrades like a ton of bricks. So, it only solves the problem in one direction? What about the other direction? High-resolution imaging still won't be possible.

Without synthesizing the aperture, high-resolution imaging is impossible; even if the aperture is synthesized, high-resolution imaging is still impossible. So, what's the point of synthesizing the aperture?
Feeling somewhat bewildered, Engineer Meng quickly regained his composure. Anyone seriously engaged in scientific research wouldn't joke around with people about basic theories. What needed to be done now was to figure out why Committee Member Gao had said that; whether it was right or wrong was a matter for later.

"Committee Member Gao, what direction is the synthetic aperture in? And how do we achieve high resolution in the other direction?"

"The direction of the synthetic aperture is the direction in which the vehicle is moving, which we can call the azimuth. Actually, this is easy to understand. Think about it: doesn't the synthetic aperture cleverly utilize the coordination between the vehicle's forward distance and the echo time to connect the radial motion of the antenna end to end, simulating a long antenna?"

The comrades immediately understood. Engineer Meng slapped his forehead: "That's right! This principle dictates that only the aperture in the vehicle's forward direction can be synthesized, because a vehicle can only move in one direction on the map projection. Therefore, there's only one direction in which the aperture can be synthesized. So that's how we solved the problem of how the other direction, which we've been racking our brains over, is synthesized! It doesn't synthesize at all!"

A question that had puzzled everyone for a long time was answered like this? The name of this synthetic aperture is so confusing! We were completely misled by the name.

In the early stages of our technological development, facing foreign technological blockades, the initial exploration was incredibly arduous. It was truly pitch black, and we could only learn by trial and error. We paid a heavy price and made many mistakes, but ultimately, we overcame the challenges.

And you know what? Only true practitioners have the chance to make a joke like this. Those who lie there and refuse to move forward are themselves a joke, they don't even need to make a fuss.

Gao Zhendong laughed and said, "Given the conditions of the sport, this is the only way we can go. The foreigners didn't completely fool us, maybe half of them, hahaha."

The comrades all laughed, and Engineer Meng's confidence soared.

"Hey, in that case, we can do a lot more in terms of orientation now. At least theoretically, it's very clear. We just need to consider the relationship between signal and motion to achieve the effect of synthetic aperture."

Gao Zhendong nodded: "Yes, although the actual situation is not that simple, that is the theory. In this way, the theoretical problem of synthesizing the aperture itself is solved."

"Yes, yes, yes! But Committee Member Gao, how do we solve the resolution problem in the other direction?" Half the problem has already been solved.

Gao Zhendong laughed: "The other direction, because it's perpendicular to the radar's direction of movement, and the main indicator between it and the radar is the distance, let's call it the range direction..."

The comrades nodded in agreement. They agreed to first reach a consensus, otherwise there would be no way to discuss it later. As for the specific name, that was up to you.

"As for how to solve the problem of high resolution in the range direction, we have actually solved it. At least we have mastered the relevant technology." Gao Zhendong was very happy. He had already laid the groundwork for this, and as one of the basic technologies of modern radar, it was impossible not to.

"Huh? It's already solved?" The comrades had been thinking that some very advanced technology was needed to solve this problem, but they didn't expect that they had already mastered the relevant technology.

Gao Zhendong smiled and said, "Don't think of SAR as too advanced. After all, this technology has been around for almost ten years. Although it is not very practical yet, at least the theoretical foundation is from eight years ago. Comrades should pay attention to this technology, but don't look up to it."

It has to be Committee Member Gao. Look at his mindset, his demeanor, his stature...

His attitude changed the comrades' views on SAR, and a good mindset is very beneficial to the progress of the work.

"Which technology that we already possess can solve this problem?" one comrade asked.

Gao Zhendong didn't answer directly, but instead went around in circles: "The answer lies in the name of the second direction. Think about it."

The comrades fell into thought.

Distance to... distance...

What is the best technology we have for solving distance resolution?
Engineer Meng slapped his thigh: "Hey! I get it now! What we've been searching for has come to us without any effort. It's right under our noses! Pulse compression! The pulse compression technology you guided us to develop when you were improving radar ranging resolution! You've done your preparatory work way too early."

The advantage of pulse compression technology is that as long as the time-bandwidth product is large enough, sufficient distance resolution can be obtained.

The other two comrades also had "that's it" expressions on their faces. It seems that Committee Member Gao had already prepared the technology in advance. The lead time was too long.

Seeing their reaction, Gao Zhendong quickly "refuted the rumors," saying it was not a good thing: "It's not that exaggerated. Pulse compression, as a basic technology for radar ranging, is not specifically designed for synthetic aperture radar. It just happens to be suitable, just happens to be suitable."

Comrades may say yes, yes, but they may not think so in their hearts. You yourself said that SAR has been around for a long time. So, as a top expert in radar, it is reasonable for you to have deployed a basic technology with many practical applications in advance, based on the application needs of SAR, a long time ago.
Judging from their expressions, Gao Zhendong knew that they probably didn't accept his denial, but there was nothing he could do about it; explaining it would only make things worse. Besides, there was no need to explain it anyway. No matter what, resolving the issue was the most important thing.

"So, with synthetic aperture in the azimuth direction and pulse compression in the range direction, does that solve the resolution problem in a two-dimensional plane?"

Meng and his colleagues were incredibly impressed. In such a simple conversation, he had clearly explained the principles of synthetic aperture radar and even solved the necessary basic technologies.

One comrade had a sudden inspiration: since things are already like this, why not use one technology to solve two problems?
"Committee Member Gao, then why not use pulse compression technology in the azimuth direction as well? Wouldn't that eliminate the need for synthetic aperture?"

Gao Zhendong laughed. "Great idea. Don't think about it again."

Of course, this was a joke. He explained, "Because in this way, the imaging algorithm simply can't keep up. Putting aside the actual technical issues, theoretically speaking, this method is far outperformed by synthetic aperture technology. Don't forget, we're developing this radar for continuous scanning imaging. SAR imaging is a two-dimensional convolution process, and the synthetic aperture process in the azimuth direction is mathematically well-suited to participate in this convolution process..."

Oh no, math doesn't lie; if math doesn't know something, it really doesn't know it.

However, as someone who works in radar imaging, Engineer Meng was clear about this: "Yes, Committee Member Gao is absolutely right. SAR is much simpler in terms of imaging than using pulse compression radar for ranging in both directions!"

Gao Zhendong smiled and said, "In fact, the effect of pulse compression is also beneficial for aperture synthesis in the azimuth direction. Moreover, SAR has another advantage, which is that after performing the necessary range migration correction, it can decouple the azimuth and range directions, further decomposing the two-dimensional processing into two one-dimensional processes..."

His words surprised and delighted his comrades.

What's astonishing is that Committee Member Gao has clearly thought about this path very deeply and far ahead; it's definitely not as simple as he says he's "interested"—his interest is terrifyingly great!
From the term "distance migration correction," we can tell that he probably already has a whole set of basic theories in his mind, and even some specific application techniques, because they don't understand the term and don't know what it is. They can only judge that it is a data correction operation related to distance.

The less you understand, the better! Such formal and seemingly profound terms indicate that Committee Member Gao is already confident in his abilities.

They walked way too fast.

As for the joy, it's naturally because Gao Zhendong has gone far and fast in this direction. What does that mean? It means everything is complete!
"Can the imaging process be broken down into two one-dimensional processes? Hahaha, that's fantastic!" Even though everyone has a digital signal processor, they all know that the simpler and faster the data processing algorithm, the better, as this leads to higher performance. One of the most remarkable aspects of digital signal processing is that, under the same fundamental conditions, it can, to a certain extent, trade processing speed for performance!

The comrades admired Gao Zhendong to an almost unparalleled degree.

Able to quickly clarify the theory and grasp the direction, able to prepare in advance for pre-processing technologies such as pulse compression and digital signal processing, and able to mathematically decompose the imaging algorithm into the simplest processing form—any one of these three qualities makes one a qualified project leader. Such qualities are rare and highly sought after.

Wait... what did he just say?
"Committee Member Gao, you just mentioned imaging algorithms?" Has he also studied imaging algorithms? This is a much deeper level than SAR theory itself.

Gao Zhendong nodded: "Yes, I took a look at it and found it quite interesting, so I couldn't resist."

Gao Zhendong felt a bit embarrassed, like a math teacher who had gone over the physics exam paper. He felt like he'd stolen everyone's work, and apologized profusely. "There's nothing I can do," he thought. "Imaging algorithms are an unavoidable part of any book on synthetic aperture radar theory. It's come to me anyway, so I can only reluctantly accept it."

The comrades had no objection to Gao Zhendong taking over the work; they were just surprised by his words.

Couldn't resist? What do you mean by "couldn't resist"? That's ridiculous! So, as long as you can't resist, you can actually do it?

(End of this chapter)