Lidars are widely used in the remote sensing of clouds,aerosols,atmospheric composition,temperature and wind speed. A great variety of lidars have been applied in atmospheric sounding,and many different methods has been used to classify these lidars in practice. A specific lidar can be named with different classification methods,and lidars in a specific category could be distinct,so it is useful to summarize the classification methods for atmospheric lidars.In this paper,atmospheric lidars are sorted out using more than 8 classification methods,and the features,advantages,and disadvantages of each lidar class are described briefly. According to the observation angle,atmospheric lidars can be divided into backscatter lidars and bistatic side⁃viewing imaging lidars (i.e.,Clidar). When the spectral features of sensors are used as the primary classification criterion,atmospheric lidars can be categorized as ordinary elastic lidars,differential absorption lidars (DIAL),Raman lidars,High Spectral Resolution Lidars (HSRL),Doppler lidars,and fluorescent lidars. According to the primary detecting target,the lidars can be named as ceilometer lidars,cloud and aerosol lidars,CO2 lidars,ozone lidars,wind lidars,and visibility lidars. According to the lidar platform,there are ground⁃based lidars,airborne lidars,and spaceborne lidars. Based on the properties of light transmitter,we have solid⁃state lidars,gas⁃state lidars and semiconductor Lidars. According to the wavelength of the transmitted laser,there are ultraviolet lidars,visible light lidars,infrared lidars,and multi⁃wavelength lidars. By the wave mode of transmitted laser,lidars can be grouped into pulsed⁃wave lidars and continuous wave (CW) lidars. Atmospheric lidars can also be considered as polarization lidars (linear polarization or circular polarization) and non⁃polarization lidars by the ability to measure the depolarization of backscatters,classified as one⁃dimensional,two⁃dimensional or three dimensional lidars by the detection space,categorized as single⁃line lidars and multiple⁃line lidars by the number of transmitted beams,or classified as single field of view lidars and multiple field of view (MFOV) lidars based on the number of field of views. In the future,more types of atmospheric lidars would occur in response to the development of lidar techniques.The relationships between different lidar categories are discussed in the paper. For example,Raman lidars,which are typically designed to be backscatter lidars with depolarization measurements,are frequently used in the detection of cloud and aerosol lidars. Differential absorption lidars,which are frequently designed to be backscatter lidars without depolarization measurements,is usually used in the measurements of gas concentration,and they can be designed be either ground⁃based or spaceborne lidars.This paper might be useful for the selection of lidars in atmospheric measurements. In practice,the type of lidar should be chosen based on the advantages and disadvantages of each lidar category according to the detection target,data quality requirements and budget.

Keywords： lidar ; atmospheric sounding ; remote sensing ; classification