This manuscript describes a low-cost holographic imager on a radiosonde, and shows that it works well, compared to other measurements. This is very important, because radiosondes often have very little information about cloud types and microphysical properties. Additionally, the manuscript is well written and well presented. I suggest publication as is. 

Summary: The authors describe the construction and testing of a radiosonde like holographic cloud droplet detector. While digital holographic detectors have been used previously in the laboratory, aircraft as well as tethered balloon or gondola measurements, this paper attempts to create a ‘disposable’ or ‘radiosonde like’ holographic detector for cloud droplet and ice particle detection. Such an instrument if successfully built will provide valuable measurements of cloud particle profiles along with regular radiosonde temperature and humidity measurements. The paper describes how the authors built the instrument and measurements from a test flight. The authors also compared their obtained cloud particle properties with other local measurements as well as satellite retrievals to showcase the accuracy of the untethered holographic instrument.

Recommendation: Reconsider with major revisions or resubmission

Overall, the context of the paper describing the new instrument design and test flight is very valuable to the atmospheric community. However, there are a few major issues with the data, the analysis and the writing of the manuscript. Due to the valuable nature of the instrument, I recommend acceptance but with major revisions. I have listed the major and minor issues below that need to be addressed by the authors before this manuscript can be considered to be published.

Revisions:

Major Issue 1: The writing

In order for this manuscript to be published, the writing needs to be significantly improved. As it currently stands, each couple of lines seem to be separated into paragraphs of their own. In a scientific article, each paragraph should represent a new idea or point. For e.g., Lines 16-20 seem to break the chain of the introduction and should be combined with Lines 59 onwards. The first paragraph (lines 11-14 can then be combined with the 3^rd paragraph lines 20-27 to create one cohesive paragraph detailing the importance of clouds and cloud observations. Conjunctions such as ‘Meanwhile’ or ‘Similarly’ can help stitch together slight changes of topics but with the same underlying idea or principle.

Major Issue 2: The RH measurements

Figures 4 & 6 show the RH values along with identified cloud bands and particle number densities. For a cloud band to exist, RH values should be close to 100% if not slightly larger. Yet cloud bands are being identified and cloud droplets and ice being detected at subsaturated conditions. Looking at Figure 4, while local peaks in RH seem to coincide with the Raspberry Pi camera and holographic images, the mean RH value seems to have an offset along with a decreasing bias with altitude. Please check and recalibrate the RH values.

Major Issue 3: Band 3 measurements

Figure 9 shows cloud particles detected by the holographic imager between 4990 and 5380 m altitude. Temperatures at these altitudes are correctly between -19 ◦C to -22 ◦C. Yet the particles look less like ice, but similar to particles from band 1 or 2. Are these images correctly labeled as band 3? A few particles also show blurring, possible due to a combination of camera and particle motion. If the particle diameters are determined by hand tracing their shape, significant errors in particle size may occur.

Minor issues:

Line 49: “Similarly, satellite based remote sensing offers wide geographical coverage”. This sentence is not similar to the previous lines and ends abruptly. Please expand on the advantages and disadvantages of satellite measurements.

Line 51: Please expand how installing instrumentation on aircrafts is complex due to aviation regulations and engineering difficulties.

Line 88: Why limit the particle motion to 1 m/s? Falling drizzle drops move at 4 m/s downwards while the balloon ascent rate is 4 m/s upwards. Is a relative speed of 8 m/s accounted for by the pulse width without generating streaks?

Line 89: 405 nm is in the Ultraviolet range. UV light is not eye-safe and eventually affects lenses, glass windows and camera detectors due to high power (Spuler & Fugal, 2011). UV coating installed on any of the lenses/glass windows? I see that a 0.9 ND filter was installed in front of the camera. Any analysis which suggests that this value is enough to protect the detector?

Figure 5: Please increase the size of the histograms. At current level, the legends cannot be read. Reducing the white space will help make it a better figure with each subplot labeled a-d.

Line 195: Please provide the average number of particles detected per hologram in order to determine if the distributions were statistically significant.

Line 245: Formation of ice at these temps is actually rare since most Ice nucleating particles (INPs) activate below -8*C Kanji et al., 2017, McCluskey et al., 2019; Vergara-Temprado et al., 2018)

Line 261: Any explanations why Band 3 and Band 2 particles look similar?

Line 352: Not sure where to look for small particles or low and mid-level clouds in Fig. 14.

Figure 14: What are the grey pixels? Are they no-cloud pixels, or no-data pixels. How are they accounted for when determining effective radius and CTH?

References:

Kanji, Z. A., Ladino, L. A., Wex, H., Boose, Y., Burkert-Kohn, M., Cziczo, D. J., & Krämer, M. (2017). Overview of Ice Nucleating Particles. Meteorological Monographs, 58. https://doi.org/10.1175/amsmonographs-d-16-0006.1

McCluskey, C. S., DeMott, P. J., Ma, P. L., & Burrows, S. M. (2019). Numerical Representations of Marine Ice-Nucleating Particles in Remote Marine Environments Evaluated Against Observations. Geophysical Research Letters, 46(13). https://doi.org/10.1029/2018GL081861

Spuler, S. M., & Fugal, J. (2011). Design of an in-line, digital holographic imaging system for airborne measurement of clouds. Applied optics, 50(10), 1405-1412.

Vergara-Temprado, J., Miltenberger, A. K., Furtado, K., Grosvenor, D. P., Shipway, B. J., Hill, A. A., et al. (2018). Strong control of Southern Ocean cloud reflectivity by ice-nucleating particles. Proceedings of the National Academy of Sciences of the United States of America, 115(11). https://doi.org/10.1073/pnas.1721627115