But what if a material could be built that had a negative refractive index , so that light was bent in the opposite direction and an object appeared to be farther from the surface than it really was 但是，要是能建立起一种具有正折射指数的物体，以致于光会朝着相反的方向折射，并且置于水底的物体看起来会比实际更远，那情况又会怎样？
But what if a material could be built that had a negative refractive index , so that light was bent in the opposite direction and an object appeared to be farther from the surface than it really was 但是，要是能建立起一种具有阴性折射指数的物体，以致于光会朝着相反的方向折射，并且置于水底的物体看起来会比实际更远，那情况又会怎样？
Underwater acoustic data acquisition equipment is necessary for underwater acoustic experimentation . since the situation underwater is very complicated , we must adopt the data acquisition equipment which is adaptive to the abominable field underwater . all of these make us to make the data acquisition equipment to has a wide dynamic range and have the utility to acquire the signals which have large amplitude range 水声数据采集装置对于水声试验来说是不可缺少的，由于水底的自然环境极其复杂，这就要求我们所采用的数据采集器能够适应水下恶劣的自然环境，因此所采用的数据采集器应具有较大的动态范围，所采集信号的幅度范围要尽可能的宽。
