General comments

The manuscript of Kollias et al. describes the algorithms prepared for the level 2 processing of data to be obtained with the EarthCARE’s Cloud Profiling Radar. It outlines the ideas used in the three algorithms, C-APC, C-FMR and C-CD. Results of performance tests of these algorithms with synthetic data sets are also shown. The paper is of use for users of EarthCARE’s level 2 products. Although the manuscript is logically correct, it suffers from numerous minor editorial errors and awkward expressions.

This paper deserves ultimate publication; however, in order for it to be published, I would recommend that the manuscript be proofread by a native English speaker before publication.

Evaluation

Does the paper address relevant scientific questions within the scope of AMT?  Yes.

Does the paper present novel concepts, ideas, tools, or data?  Yes.

Are substantial conclusions reached?  Yes.

Are the scientific methods and assumptions valid and clearly outlined?  Yes.

Are the results sufficient to support the interpretations and conclusions?  Yes.

Is the description of experiments and calculations sufficiently complete and precise to allow their reproduction by fellow scientists (traceability of results)?  Yes.

Do the authors give proper credit to related work and clearly indicate their own new/original contribution?  Yes.

Does the title clearly reflect the contents of the paper?  Yes.

Does the abstract provide a concise and complete summary?  Yes.

Is the overall presentation well structured and clear?  Marginally yes.

Is the language fluent and precise?  No.

Are mathematical formulae, symbols, abbreviations, and units correctly defined and used?  No.

Should any parts of the paper (text, formulae, figures, tables) be clarified, reduced, combined, or eliminated?  Yes.

Are the number and quality of references appropriate?  Yes.

Is the amount and quality of supplementary material appropriate?  N/A.

Specific comments, suggestions and questions

In general, all acronyms must be spelled out in their first appearances. Acronyms such as C-APC, C-FMR, C-CD (P.2, l.31) must be spelled out in the main text, since the abstract is not regarded as a part of the main text.

Almost all subscripts to mathematical symbols are italicized in the text. Such identifiers should not be italicized unless they are variables. (Example: Subscript ‘noatt’ to ‘sigma’ should not be italicized.) Similarly, the SI symbol for second is roman letter ‘s’. It should not be italicized. Many s in ms-1 are italicized in the text (e.g., page 15, lines 339, 341, 346 and 347).

P.1, L 16, “demonstrate’ -> “demonstrates”

P.2, l 22, What are “the three instruments’?

P.2, l 26, Add “than CloudSat” at the end of the sentence.

P.2, l 27, Add “the minimum detectable radar reflectivity factor is” before “-36 dBZ”.

P.2, l. 29, “L2B” -> “L2b”

P.2, l.32, “is” -> “are”

P.2, l.33, “C-ATC”-> “C-APC”

P.2, l.37, “(van Zadelhoff et al., 2022)” -> “van Zadelhoff et al. (2022).”

P.2, l.39, “CPR On board processing’ -> “CPR onboard processing”

P.2, l.52, “The return signal from each pulse results to another pair of I/Q at each range gate that includes contributions from the atmosphere (signal) and the radar receiver (noise).” The meaning of this sentence is obscure. What do the authors mean by “another pair of I/Q”?

P.3, l.1, What are “the CPR Doppler radar moments”? Aren’t they the Doppler spectral moments?

P.3, l.59, “21-22 consecutive I/Q pairs”. According to the description a few lines below this expression, 22 pulses are used to estimate R(r,tao). Only 21 I/Q pairs can be made from 22 pulses. How does the processing unit use 22 consecutive I/Q pairs?

P.3, l.70, equation (3), R(r,tau) -> |R(r,tau)| , needs to take the absolute value.

P.3, l.73, “angle” -> “angles”

P.3, l.73, “the velocity of the satellite along the flight direction, in the direction orthogonal to the orbit plane and the nadir direction.” What does this phrase mean? Does it mean “the velocities of the satellite along the flight direction, in the direction orthogonal to the orbit plane and the nadir direction.” (Shouldn’t the “velocity” be plural?) If so, isn’t the velocity in the direction orthogonal to the orbit plane always zero by definition? Or do the authors refer to the motion of the orbit plane relative to the rotating Earth?

P.3, l.79, “as a function of along-track distance, the hydrometeor-induced path integrated attenuation (PIA).” -> “as a function of along-track distance, and the hydrometeor-induced path integrated attenuation (PIA).”

P.4, Figure 1 (c), Why do the Z values at distance between 3500 and 3600 and height below 2 km larger than the corresponding Z in (b)?

P.5, l.94, “This explains the missing hydrometeor locations in the low levels around 3780 - 3800 and 4050 - 4180 km” The intervals specified by this sentence must be wrong. They must be around 3740-3760 and 4070-4130.

P.5, l.100, “detection’s .” -> “detections.” (remove the apostrophe and the extra space after ‘s’.)

P.5, l. 104, “detection’s .” -> “detections.” (remove the apostrophe.)

P.5, l. 108, “Path Integrating Attenuation” -> “Path Integrated Attenuation”

P.5, l. 117, “measured surface echo” -> “measured surface cross section”

P.6, l.122 and l. 123, What does X-MET stand for? Which is the correct form, “X-MET” or “X-Met”?

P.6, l. 124, “sigma_0” -> “sigma_{clr}”

P.6, l.128, “range resolution” -> “range sampling interval”

P.6, In figure captions to Fig. 2, Fig. 3, Fig. 4, and l. 157, “C-PRO” is not defined.

P.7, Fig. 3, The figure caption needs a period at the end of the caption.

P.7, Fig. 3, Some explanation is required for the plot of the PIA and True PIA at the top of the figure. It seems to be a histogram.

P.8, l. 169, “… Battaglia et al., 2013; ?)” Replace the question mark with a meaningful word.

P.8, l. 172, “between 6100 and 7400 Hz”. This interval of PRF does not agree with the interval “between 6.2 and 7.4 kHz” written on page 2, line 51.

P.9, Fig. 4, The figure caption needs a period at the end of the caption.

P.9, Fig. 4, What are the conditions for ‘Strong MS’ and ‘MS’? No regions marked by MS appear in Fig. 4.

P.10, l. 185, “The JAXA CPR L1b data product (C-NOM), includes satellite …” -> “The JAXA CPR L1b data product (C-NOM) includes satellite …” Delete the comma after (C-NOM).

 P.10, l. 203, “Tanelli et al. (2002); Kollias et al. (2022) have …” -> “Tanelli et al. (2002) and Kollias et al. (2022) have …”

P.10, l.206, “Others configurations” -> “Other configurations”

P.10, l. 208, “Each point x0 in the along track direction” -> “Each point x0 in the along-track direction from the beam center”

P.10, l.209, “velocity vSAT” -> “along-track velocity vSAT” (The altitude of the satellite may change with time. This vertical velocity is not included in equation (7).)

P.11, l.218, “Tanelli et al. (2002); Sy et al. (2014)” -> “Tanelli et al. (2002) and Sy et al. (2014)”

P.11, l.228, “the complex R(tau) lag-one of the radar complex signal” -> “the lag-one autocovariance R(tau) of the radar complex signal”

P.11, l.242, “exceeds VN.” -> “exceeds the phase that corresponds to VN.”

P.12, l.258, “eta=1”, In order to be consistent with this statement, the negative sign before eta in equation (13) should be deleted and “eta is an integer (0, 1, 2, …)” in line 244 should be modified to “eta is an integer (…, -2, -1, 0, 1, 2, …)”.

P.12, l. 262, “Signal-to-Noise” -> “signal-to-noise”

P.12, l.268, What are the C-CLD and ACM-CAP algorithms?

P.12, l.274, “Lx (km)”, “Lz (km)” -> “Lx”, “Lz”. Delete unnecessary (km) to be consistent with the statement in line 278 in which Lz is specified in m.

P.13, l.289, “Fig.5a shows an example of the reflectivity-weighted hydrometeor sedimentation Doppler velocity.” The sedimentation velocity is the sum of the hydrometer fall velocity and the vertical air velocity. There seems to be no negative sedimentation velocity regions in Fig. 5a. Doesn’t the GEM model include any significant updraft area? (This question is also applicable to P.15, l.331, “The SVBE estimates are always positive.”)

P.13, l.300, “affects” -> “affect”

P.15, l.326, “the probability of finding 5 CPR Values” -> “the probability of finding at least 5 CPR Values”

P.15, l.335, “Each estimate is compare against” -> “Each estimate is compared against”

P.15, l.341, “2.5 ms−1 Fig. 6a.” -> “2.5 ms−1 (Fig. 6a).”  “s” in ms-1 should not be italic. (This comment is applicable to several other places.)

P.15, l.346, “1.8 ms-1”. Judging from the data in Fig. 6, this velocity should be 1.6 ms-1.

P.17, l.369, “(Battaglia and Kollias, 2014b)” -> “Battaglia and Kollias (2014b)”

P.17, l.372, “ ice clouds radar reflectivity weighted mean Doppler velocity”. Awkward.

P.17, l.374, “flow chart” -> “flowchart”

P.17, l.374, “The C-APC required input data are: the JAXA CPR L1b C-NOM and the X-MET files.” -> “The input data to C-APC are the JAXA CPR L1b C-NOM and the X-MET files.”

P.17, l.381, “Kalesse and Kollias (2013))“ -> “Kalesse and Kollias (2013)“

P.19, l. 394-399, The reviewer was not able to understand this paragraph well enough. What does “each 1/8 of an orbit long data files” mean? Is it ‘each data file that includes 1/8 of an orbit?

P.19, l.412, “more noisy” -> “noisier”

P.19, l.415, “polynomial fit”. Why is the harmonic fitting used in the case of Earth’s surface, but the polynomial fitting used in the case of ice clouds?

P.21, l.435 and 441, “L2A” -> “L2a”

P.21, l.435, “The CPR feature mask and reflectivity (C-FMR) product physical basis and algorithm structure is …”, Do the authors mean by this subject “The physical basis and algorithm structure of the C-FMR product are …”?

P.21, l.437, “and in combination with the improved sensitivity is expected to lead to more detections of low-level oceanic clouds (Burns et al., 2016).” What is the subject of this sentence?

P.21, l.444, “however,” -> “However,”

P.21, l.449, “the SVBE, that” -> “the SVBE that”

P.21, l.459, “will be’ -> “is”

Reviewed by Matthew Lebsock

This paper describes three radar-only algorithms for the upcoming EarthCARE mission. The algorithms presented include a vertical feature mask, a Doppler correction product, and a pointing characterization product. The presentation is technically correct and relatively straightforward. The paper will provide an important citation for the at-launch product suite. I have only minor revisions regarding a few details of the presentation and some missing citations.

Line 25: add ‘Cloud Profiling Radar’ or ‘radar’ after CloudSat.

Line 25: change ‘compare’ -> ‘compared’

Section 2: It would be useful for many readers to understand the relationship between the three algorithms described here within the larger suite of EarthCARE products. Can an algorithm flow chart be incorporated? Or at least in words described?

Lines 93-95: The non-expert reader is not going to know what you are referring to. Add wording to the effect of ‘beneath the convection near 4100 km’.

Line 112-114: Mention the small temperature dependance.

Line 114: Cite Lebsock et al., 2011 https://doi.org/10.1175/2010JAMC2494.1,

Lines 122 and 123: Is it X-MET or X-Met?

Lines 140-145: Lebsock and Suzuki, 2016 (https://doi.org/10.1175/JTECH-D-16-0023.1) discuss the errors in this approach including (1) attenuation by undetected clouds, (2) systematic differences between water vapor in clear and cloudy columns, and (3) non-uniform beam filling (NUBF). The first two are small for the shallow subtropical cumulus clouds where this approach is best implemented. NUBF errors can be significant.

Section 3.2 Regarding Non-uniform beam filling errors for PIA - Even if you estimate a perfect PIA (averaged over a footprint) you have to translate that PIA into a TWP. The NUBF changes the relationship between PIA and TWP which can introduce significant errors. I understand the product won’t produce a TWP but this limitation in the utility of PIA for deriving TWP deserves mention somewhere in the PIA section.

Section 3.2 You should mention somewhere in this section that MS signals frequent in stronger precipitation are often going to bias the PIA estimate low.

Line 154: Cite MS model.

Line 169: ‘?’ as a reference.

Section 4.1.2: This section is too general. You don’t describe the specific EarthCARE algorithm. Can you provide some details here on how you do the unfolding?

Line 341 add ‘()’ around ‘Fig 6a’

Line 432: add ‘than cloudsat cpr’