题目

Sonar (声呐) allows for clearer visual imaging underwater compared with the conventional signal processing method of visualizing sound echoes. Underwater imaging sonar is an essential technology for ocean exploration. Sonar inspired by marine mammals such as dolphins is an emerging development in this field.Scientists from the National University of Singapore observed that dolphins were able to acoustically (听觉上) scan objects underwater and pick matching objects visually. This demonstrated that a dolphin's sound echoes emitted off an object contained information about the object's shape. They then recorded dolphin echoes emitted when scanning an object underwater.Based on their observations, the team built a sonar system that copied a dolphin's sonar. The sonar, which is about 25 cm in width and around the size of a dolphin's head, is designed to emit sharp click sounds similar to a dolphin's echolocation (回声定位). Three transmitters are used to send sounds from different directions. The researchers then processed the sounds from both dolphins and their sonar to visualize what the echoes revealed about the object's shape. To make the most of this new hardware, the team developed a novel processing algorithm (算法) that allowed the sonar to improve the visualization of the echoes. Based on the hypothesis that dolphins use prior information to process their echoes, the researchers included prior information in their algorithm.The effectiveness of the software was demonstrated when it was able to visualize information from a dolphin's sonar echoes when scanning an object, as well as sonar signals produced by their sonar. A conventional approach to processing both sonar echoes resulted in noisy images. However, the novel processing approach gave better resolution and, therefore , sharper images. The software was also able to generate visualization with a mere three clicks from the sonar, allowing it to be operationally fast.The new sonar processing method could have potential benefits in underwater commercial or military sonar. For example, it could be used to scan the seabed to search for features that can be used to aid navigation. The sonar's compactness (小巧) also makes it suitable for installation on underwater robots for ocean exploration. （1） What did the scientists observe about dolphins? A . They could send visual signals to communicate. B . They could identify underwater objects by sight. C . They could change the shape of objects through sound. D . They could recognize the shape of an object based on their echoes. （2） What do we know about the sonar built by the researchers? A . It has a length of 25 cm. B . It exploits military technology. C . It contains multiple transmitters for sound emission. D . It translates the sound of dolphins into visual signals. （3） How did the new processing method differ from the conventional approach? A . It generated more noisy images. B . It produced images with better clarity. C . It did not rely on advanced technology. D . It required less human intervention for operation. （4） What is the main focus of the text? A . The potential benefits of underwater imaging sonar. B . The introduction of a dolphin-inspired sonar technology. C . The observation of dolphins' acoustical scanning abilities. D . The comparison between conventional and new sonar methods. 答案： D C B B

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