If underwater cultural relics are exposed at a certain height above the seabed or riverbed and are regularly distributed over a certain area, then we can use side-scan sonar and multi-beam sonar equipment.
As is well known, in May 2023, the National Cultural Heritage Administration made an official announcement that China had discovered for the first time two large ancient shipwrecks, No. 1 and No. 2, in the deep sea of the South China Sea. The number of cultural relics is considerable and they are relatively well-preserved, with extraordinary historical, scientific and artistic value. The No. 1 and No. 2 shipwrecks date back to the Hongzhi period and the Zhengde period of the Ming Dynasty respectively. During the exploration process, underwater archaeologists used the submersible-mounted depth and side-scan sonar independently developed by the Chinese Academy of Sciences to obtain a global distribution map of the underwater area of the shipwrecks. Please take a look at the pictures, friends.
Let''s start with the side-scan sonar equipment. When using side-scan sonar, we periodically send a short sound wave pulse to one or both sides of the vertical direction of the measurement vessel''s course. It should be noted that the horizontal opening angle of the short sound wave pulse is very small, while the vertical opening angle is very large. When the short sound wave pulse reaches the seabed, it will be reflected continuously according to the distance from the seabed to the transducer, and the reflected signals of different intensities will be recorded as points of different gray levels. In this way, we can observe the changes in the seabed topography and infer whether there are any relics or remains protruding from the seabed surface. While using side-scan sonar, we also use a computer image processing and recognition system to analyze the size, shape and depth of the seabed targets. It should be said that the principle of side-scan sonar is very simple, but its application still has limitations. Because, with side-scan sonar, we can only observe the changes in the seabed topography, but if we want to confirm the suspicious points and conduct detailed exploration, we still have to rely on human efforts, that is, the underwater archaeologists'' diving exploration.
So, what is a multi-beam sonar device? The picture shows the "multi-beam sonar image of the remains of the Jingyuan warship" sent back from the sea area of Hei Island, Dalian in the autumn of 2014. Friends can see that the image still has a certain degree of recognition, which is because part of the Jingyuan warship is exposed above the seabed.
Theoretically speaking, multi-beam sonar equipment can provide the water depth values of dozens to hundreds of points on the seabed within a plane perpendicular to the course at one time, and then form a full-coverage water depth strip of a certain width. Therefore, compared with side-scan sonar, multi-beam sonar can better reflect the subtle undulations of the seabed topography. Generally speaking, the multi-beam depth measurement system has the advantages of wide measurement range, fast measurement speed, high precision, digital recording and real-time automatic mapping. It can expand the depth measurement technology from the original point and line to the surface, and conduct three-dimensional depth measurement and automatic mapping, efficiently and qualitatively completing the seabed survey work. Nowadays, multi-beam sonar equipment can excellently complete the seabed topography detection. In underwater surveys, this equipment is widely used to detect protruding seabed objects that are relatively high and large in size, such as cultural relics piles and shipwrecks, as well as to detect the seabed topography and understand its topography, water depth and other data, providing materials and basis for further diving exploration by underwater archaeologists. Of course, like side-scan sonar, multi-beam sonar equipment also has limitations. That is, its resolution is not large enough to clearly present the features of small cultural relics and shipwrecks.
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At this point, we have a question. If underwater remains are buried beneath the seabed surface, side-scan sonar and multi-beam sonar may become ineffective. So, what hardcore equipment will we use to complete the geophysical survey work? Please watch the 34th episode of "Superman Underwater Classroom". See you in the next episode. 现在，我们有一个问题。如果水下残骸被埋在海床表面以下，侧扫声纳和多波束声纳可能会失效。那么，我们将使用哪些核心设备来完成地球物理调查工作呢？请看第34集《超人水下教室》。下一集见。
Pressing the video recording function on his phone, Guo Chaoren let out a long sigh of relief. 按下手机上的录像功能，郭超仁长舒了一口气。
The 33rd micro-lesson has finally been recorded. It wasn''t easy! 第33节微课终于录制好了。这可不容易！
Last night, I indulged in spicy crayfish. I didn''t pay attention to the dryness and soreness around my lips and on my tongue in the middle of the night. When I looked in the mirror this morning, I found that my lips were as red as cooked shrimp and as swollen as sausages... 昨晚，我大吃了一顿辣小龙虾。半夜里，我没有注意到嘴唇周围和舌头上的干燥和疼痛。今天早上照镜子的时候，我发现我的嘴唇红得像煮熟的虾，肿得像香肠……
After scolding himself in his heart, Guo Chaoren had no choice but to move the recording time to the evening. 郭超仁在心里骂了自己一顿，无奈之下只好把录音时间改到了晚上。
Looking out of the window at the flashing neon lights, Guo Chaoren glanced at his phone to confirm that it was nine o''clock in the evening. He hurriedly shouldered his backpack, closed the door and rushed downstairs. 看着窗外闪烁的霓虹灯，郭超仁看了一眼手机，确认已经是晚上九点了。他赶紧背上背包，关上门，冲下楼去。
As Guo Chaoren was about to take out his earplugs after leaving the "Shanghai Underwater Archaeology Research Institute"【Note 1】, he was suddenly blocked by a long-haired girl. 离开“上海水下考古研究所”后，郭超人正准备拿出耳塞【注1】，突然被一个长发女孩挡住。
"Hi, Super Ren Brother." “你好，超级仁哥。”