The manuscript describes the performance of the Chinese aerosol space lidar DQ-1 HSRL. This manuscript will be probably one of the fundamental papers on  DQ-1 HSRL. Therefore, the quality of the manuscript must be improved. Much more information about the quality of the measured signals, about calibration and quality assurance efforts, about cross talk in the different measurement channels needs to be provided.

Major revision is thus recommended.

Detailed comments:

Abstract:

What is the meaning of DQ-1 (DQ stands for…?, should be explained…).

I would suggest not to use dB to characterize signal-to-noise ratios or the cross talk impact. Just use signal ratios such as P1/P2 instead of Q = 10 log (P1/P2) in dB.

In the abstract, R^2 0.803, you mean R^2=0.803? 

Introduction

line 53: The shortcomings of airborne (and spaceborne) observations could also be mentioned: They deliver snapshot-like observations, compared to ground-based (GB) observations. GB remote sensing may allow to study life cycle processes, evolutions, developments.

lines 66-68: The text is confusing, please rephrase!. Furthermore, one could mention other activities such as the AEOLUS and the EarthCARE space lidar missions, in support to CALIPSO.

line 79: …  to be launched…when?

line 82: What does DQ mean? Please explain!

Instrumentation and method

line 112: There are three signal channels: cross-polarized (particle+Rayleigh), co-polarized (particle+Rayleigh), and HSRL channel (Rayleigh). Please add this information on particles and Rayleigh contributions.

line 117: You mention, the aerosol suppression ratio is more than 25 dB. So, we have less than  -25 dB, i.e., less than 0.00316). Is that sufficient to derive extinction profiles? In the case of cirrus backscatter and extinction, you may need 5-6 orders of magnitude suppression to obtain high-quality extinction profiles? But maybe you correct for cross talk? But that should then be explicitly described.

DQ-1 detects co and cross-polarized Rayleigh and particle backscatter components. We need to know, how large the contribution of these four signal components is in the three measurement channels? Is all the cross talk considered and corrected for in the different product retrievals?  How are the transmission and reflection properties of the optical elements in the receiver unit, between the telescope  and the detector. What is the contribution of the four signal elements to the detected signal counts in the three channels.

All potential cross talk effects must be considered in the retrieval. So, please discuss the contribution of the four backscatter components in the three channels.

The Eqs.(2.1)-(2.3) are too simple! No efficiency factor (describing  optical and detection efficiency), no cross talk factor!

An Eq.( ) for T_m would be nice.

Please state in the mansucript where you found Eq.(2.4).

So, Eq.(2.5) does not need any calibration? The depolarization ratio is simply obtained from the ratio of the cross- to- co-polarized channel outputs?

Please provide a reference for Eq.(2.6)!

Two times the same equation: Eq.(2.6) and Eq.(2.8).

Please, provide reference for Eq.(2.9). What is the solution for Eq.(2.9) if you start fromEq.(2.8) (or Eq.(2.6))?  

line 175: Please explain all abbreviations when they appear for the first time!

line 184:  Pappalardo et al. (2014) deal with the EARLINET lidar network, not with the MPLNET.

line 191: For HYSPLIT we need a references.

Validation of the retrieval results

line 227:   … with a 10^-4 m^-1 values …. What does it mean? What do you want to tell us?

line 228:   … with a value of 10^-5 m^-1 sr^-1. …. What does it mean? What do you want to tell us?

lines 222 and 234: the same … I do not understand!

line 245: CALIPSO does not measure the lidar ratio! The lidar ratio is an input value in the CALIPSO data analysis. The lidar ratio has to be set! Note,the lidar ratio dimension is sr and not sr^-1.

line 247: In case of CALIPSO measurements of marine particles the lidar ratio is set to 20 sr. The dimension sr^-1 is wrong.

What about the measured lidar ratios (DQ-1 HSRL), measured within the cirrus at 15 km height? Please discuss the values. This is one of the important new products of a spaceborne HSRL, compared to the CALIPSO products. Should be highlighted!

Regarding cirrus and specular reflection! Is the lidar zenith or off-zenith pointing?

MPL is an elastic backscatter lidar as the CALIPSO lidar. This lidar type only delivers profiles for the backscatter coefficient. This lidar cannot measure extinction coefficients and lidar ratios.

line 281: At the end of the section, what about the lidar ratios measured with the DQ-1 lidar?

line 313: You mean top height of 8 km or base height of 8 km? Please, specify.

line 320: You may also check these papers regarding long range transport towards the Caribbean:

Haarig et al., Atmos. Chem. Phys., 17, https://doi.org/10.5194/acp-17-10767-2017

Rittmeister et al., Atmos. Chem. Phys., 17,  https://doi.org/10.5194/acp-17-12963-2017

Ansmann et al.,  Atmos. Chem. Phys., 17, https://doi.org/10.5194/acp-17-14987-2017

Section 4: Why not showing height profiles of extinction, depolarization ratio, and lidar ratio in addition.

Figure 1: One should indicate the different channels (B, B_C, B_H)

Figure 4e: Please mention that mean profiles for 20-22°N (longitudes…?) are shown.

Figure 5: the color range should be improved. We have mostly dark blue, sometimes light blue (or cyan) and sometimes yellow. The advantage of DQ-1 HSRL is that lidar ratios can be measured. But lidar ratio results are not shown in Figure 5 (i:backscatter, j: extinction, why not k: lidar ratio). and also, what about depolarization ratio results?

Figure 6: MPL retrievals can only deliver particle backscatter profiles. If extinction profiles obtained with MPL and DQ-1 HSRL match then this is just the hint that the lidar ratio was around 50 sr, as assumed  in the MPL retrieval. What about depolarization profiles.

Figure 7: Again, only backscatter can be compared.