Good question.

> What makes lidar a better choice for many applications, including archaeology, is that the wavelength is about half a micron – tiny relative to radar wavelengths, which are measured in centimetres or decimetres. For details of a relatively small spot on the ground, lidar provides a precision that radar cannot match.

Source: https://www.theguardian.com/science/2015/jun/20/lidar-radar-...