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Solar Background Radiation Temperature Calibration of a Pure Rotational Raman Lidar

Vasura Jayaweera, Robert J. Sica, Giovanni Martucci, and Alexander Haefele

https://doi.org/10.5194/egusphere-2024-1081 Preprint. Discussion started: 7 May 2024

General comments

This paper addresses a nice and useful subject. It is interesting because the method presented can be used in lidars that use the pure rotational Raman lidar technique for temperature profiling. However, I find that the paper is poorly structured, which makes it a nuisance to read, and therefore obscures the essence of the material offered.

Therefore, I should like to keep this review very short, as I recommend the authors to basically re-write the paper.

A number of comments to be taken into account:

• There is no general description of the RALMO lidar. The paper should al least have a simple but adequate schematic of which channels are used and how these channels come about. An accompanying table listing the instrument specifications should also be added.
• The system constants in Eq. 1 require a bit more introduction. The lidar equation for PRR temperature should be introduced first.
• ‘GRUAN’, not ‘GRAUN’
• In contrast to the ack of an overall system overview, the Licel (digitisation system) is mentioned a couple of times, without explaining what it is. Is it the Analog/photon counting combination that is referred to or merely the digitised signals?
• A number of references to in-depth descriptions of the Raman lidar technique for water vapour and temperature lidar, including error analysis are missing. E.g.
  • David N. Whiteman, "Examination of the traditional Raman lidar technique. I. Evaluating the temperature-dependent lidar equations," Appl. Opt. 42, 2571-2592 (2003).
  • Leblanc, T., Sica, R. J., van Gijsel, J. A. E., Haefele, A., Payen, G., and Liberti, G.: Proposed standardized definitions for vertical resolution and uncertainty in the NDACC lidar ozone and temperature algorithms – Part 3: Temperature uncertainty budget, Atmos. Meas. Tech., 9, 4079–4101, https://doi.org/10.5194/amt-9-4079-2016, 2016.
• I recommend restructiring the manuscript to first clearly describe the methods used to retrieve the temperature profiles.
  • In the results section an optimal estimation method appears out of the blue. The term OEM is not explained.
  • Also a description of the GRUAN sonde products is needed. Was the uncertainty information in the GRUAN profiles used?
• Please add some clarifying labels to Figure 1 to guide the reader. E.g. where is t0? What happens sometime in 2012 (make reference to the text) and also just before 2013?
• I believe that the continuous background method can be used to monitor sudden changes in instrument behaviour by following the value of the calibration constant. However, an external source is always needed for an absolute calibration. Therefore, the accuracy is always limited by the accuray and uncertainty of the external reference and, in this case the uncertainties of the lidar. This needs to be further elaborated.