To see this, you can picture that the raindrop themselves are stationary, and you and the earth beneath you are moving upwards through the rain.

想要了解这个，你可以想象雨滴本身是静止的，而你和脚下的土地在雨中向上移动。

youdao

As one of the best tools to analyze the non-stationary signals, it shows a good picture in the joint time-frequency domain and makes us know about the change of frequency along with the time clearly.

这种分析方法提供了时间域与频率域的联合分布信息，清楚地为我们描述了信号频率随时间变化的关系。

youdao