How deep is the ocean? Is the seabed rugged or smooth? For millions of years, these problems have constantly inspired mankind to explore the mysterious world under the sea. For a long time, sailors have used "sounding lines" to estimate the depth of the ocean. They put a rope of known length into the sea until the weight on the rope touched the bottom of the sea. According to the length of the rope, they know the depth of the ocean. But this method is slow and unreliable. Because when a heavy object enters the deep sea with the falling rope, it is difficult to judge whether it has touched the bottom of the sea and whether the rope is tight at this time. The study of the deep sea began with HMS Challenger, a research ship converted from a British warship. 1872 65438+maiden voyage in February, with the task of "understanding the ocean comprehensively". Challenger made a comprehensive study of the global ocean for the first time. The steamboat crossed all oceans except the Arctic Ocean. It sailed 68,890 miles with 273 crew members and 6 scientists. Under the leadership of Sir Vivelli Thomson, all the physical and biological factors that may affect aquatic organisms were studied. All the crew on board * * * made 492 sounding and 133 sampling. Every time they measure, they struggle to put the rope with heavy objects into the sea. Finally, the Mariana Trench is about 27,000 feet deep, which proves that the ocean is much deeper than people think. At the same time, they also dug up samples of seabed sediments for further study and discovery of new species. Although the voyage brought back a wealth of data (the voyage report has 50 volumes), human understanding of the seabed is still superficial. Through once and for all measurement, we can fully understand the vast underwater world. After that, the number of voyages increased and the data gradually accumulated. 1920, due to a technological breakthrough, people can use sound waves to detect the seabed. Through electronic echo detector (later called sonar), people can make accurate depth measurement. The echo detector is installed on the ship and can measure the time required for an acoustic pulse to reach the seabed and reflect. Divide this time by two and multiply it by the average speed of sound in seawater (4925 feet per second) to get the depth of the ocean. By drawing continuous echoes, we can have a general understanding of the seabed. 1922, the new technology was first used by the American Stewart, and 900 echo measurements were made. Then, German meteor explorers brought natural oceanography into a new field. From 1925 to 1927, it crossed the South Atlantic for fourteen times and collected more than 70,000 sounding data. From these data, we can know that the seabed is rugged. Now, scientists take another way-space satellites to understand the seabed. The satellite is equipped with an altimeter to measure the exact depth of the ocean by radar. This depth will be different because of the different gravity on the seabed. Mid-ocean ridges, seamounts, trenches, etc. The density of the crust is different, so the attraction to the sea surface is different. Computers use these data to infer the situation on the seabed.