A certain year, a certain month, a certain day.
a sea area.
200 meters below the ocean surface.
twilight zone.
At this depth underwater, the sun is as dark as dusk.
Looking down, there is a dark abyss below.
Looking up, the above is like the short period of blue sky after the sun sets and before the sky is completely dark.
Different from the real sky, there is no bird returning to the forest here. Occasionally, there will be a streamlined shadow swimming quickly far above the head, which is a large shark in the shallow sea.
This depth is beyond the reach of at least half of marine life, but in the faint light, something is still moving quietly.
call
A shadow swam by at an extremely fast speed, its body reflecting a dim silver light, and few things could cruise at such a speed in the sea.
It was an adult swordfish with a body length of nearly two meters. With its long jaws shaped like fencing, it swam recklessly. In the ocean at this depth, with its excellent speed, it had almost no natural enemies except sharks. .
Its eyes are very big, the size of tennis balls, with a large number of photoreceptor cells distributed. It is impossible to hunt under this level of light without some peculiarities in the body.
Sharp long jaws, keen eyesight, a body weighing hundreds of catties, and a short-distance sprint speed of more than 100 kilometers, it has acquired a proud capital. It is as terrifying as a harpoon when it is mad, and it even has " The good name of "wearing wood boards every day"...
This swordfish has had bad luck today, hasn't found anything to eat yet, hunger has turned him into a grumpy old man, and he's looking for something out of the way to live with, anything.
In front of its high-speed swimming route, a big black guy suddenly appeared, with a slow swimming speed, seven out of ten whales.
Even the fastest whale can't eat the exhaust of swordfish, so it has the confidence to challenge it.
It may be that its speed is too fast, so fast that it rushed over without even seeing what the opponent was. It didn't realize something was wrong when it got close, and hurriedly twisted its strong muscles to make a sharp turn, barely avoiding the opponent The opponent's collision.
what happened? Why is this guy's body so long? It is much longer than the largest whale it has ever seen, with a round head, a "dorsal fin" as thick as a reef, pectoral fins that are almost invisible, and a caudal fin that rotates periodically to stir the sea water. Stupid whale... The most important thing is that the opponent's skin seems to be much tougher than a wooden board.
Forget it, let's find a soft persimmon and pinch it.
It flicked its tail, swam away resentfully, and disappeared into the dim light.
The nuclear submarine, mistaken by the swordfish for a whale, cruised silently underwater at a speed of 6 knots. Along the way, it passed under dozens of different types of ships, including fishing boats, cargo ships, oil tankers, and private yachts. He even ventured into close contact with warships, but fortunately was not discovered by any ships.
Behind it drags a long "tail", which is longer than any tail in nature, with a total length of almost 1 kilometer, including 800 meters long and less than 1 centimeter in diameter tow cable and more than 100 meters long, composed of thousands of A sonar array of hydrophones.
The towed sonar array works at a wavelength below 3000 Hz, and the lowest effective frequency range is 10 to 20 Hz. Through the deep-sea sound channel and the convergence area effect, the longest detection distance reaches 180 kilometers, and it can even be obtained outside the territorial waters of other countries. Information and topographic features.
Narrow sonar chamber.
Sonarman No. 1, wearing a military uniform and headphones, stared intently at the screen in front of him, looking for traces of enemy nuclear submarines.
All the sounds from within a range of 180 kilometers are captured by the sonar array, amplified by the output, and transmitted to the earphone of No. 1 sonar operator, and the waveform diagram is displayed on the screen in front of his eyes through the tuning indicator.
Sonarman No. 2 sitting next to him is responsible for the operation of the bow sonar and echo sounder.
Sonarman 1 periodically switches the button and adjusts the filter, sometimes gaining low frequency and sometimes high frequency, in case an enemy submarine is quietly approaching in the sound shadow area.
The thin stubble around his lips proves that he is very young, but he has been on duty in this submarine for a year, and he is not a recruit who panics when encountering things, as can be seen from his calm and experienced expression.
Various voices sounded alternately in the earphones, and he knew most of them well. If not, he would not be qualified to disembark and become the eyes and ears of the submarine.
Nuclear submarines are very quiet, making very little noise themselves, and far less noisy than diesel submarines during operation.
He can distinguish the crisp crackling sounds of shrimps bouncing their bodies, the sharp calls of dolphins, the unpleasant grasshopper sounds of golden drum fish, and the cooing sounds of large yellow croakers like frogs... This kind of The unbelievably sharp insight in the imagination of others is just a part of work and training for him. He has no hearing that is different from ordinary people, but the more he hears, the more he remembers nothing but familiarity.
Suddenly, his straight eyebrows moved slightly, and a strange voice was caught in his ears, which disappeared in a flash.
He didn't let go of any abnormalities. The waveform on the screen just now remained in his memory. He adjusted the buttons intuitively, turned on the low-pass filter, and increased the low frequency.
That voice is back.
He rolled his eyes quickly, glanced at the frequency slightly, and found that the range of the sound was between 45 and 50 Hz.
Is it a whale
Submarines often encounter whales. He is familiar with the sounds of various whales. In his memory, some whales can indeed make sounds in this frequency range, but the specific calls are different from the ones he heard just now.
"No. 2, please confirm the direction, frequency band 45-50." He said.
Since the towed sonar is a straight line, it is difficult to confirm whether the source of the sound is from the port side or the starboard side. Other sonar assistance is needed, or it can be confirmed by the submarine maneuvering, but the submarine in the cruising state cannot change just because of a slight abnormality. direction, so you can only choose the former.
"Understood." The No. 2 sonar officer answered simply and neatly, and also adjusted the bow passive sonar to a low-frequency gain of 45 to 50 Hz.
The same young sonar operator No. 2 stared and listened for a while, and said, "Location 090, identity is unknown."
"Got it!" said sonar operator No. 1.
"Sir!" He took off his headset and called the officer on duty.
"What's up?"
The officer on duty immediately walked over quickly, making a loud noise. He is much older than sonar operator No. 1, and he is mature and experienced in the true sense, as evidenced by the wrinkles at the corners of his eyes and the military rank on his shoulders.
"Suspicious contact, bearing 090, sound like a whale." Sonar No. 1 reported concisely. 8)