The authors present a thorough investigation of the RO data quality of the FY3 satellites, using as reference ERA5 data and comparing it to a high-quality RO receiver (Metop-C). The quality is assessed using both ionospheric-corrected and statistically optimized bending angles. Comparisons are also performed for derived refractivity and temperature profiles.

The results are useful and they could benefit from some changes and more information on a number of topics, listed below under “Main comments”. Included are also minor comments and a list of language suggestions.

Main comments:

Consider adding a description of the FY3 mission (e.g., orbital configurations, main features of the different satellite buses, description of the RO antennas, etc.).  Having this information would make it easier to assess statements like the one on Ln 180-181 (“This suggests that the GNOS BDS RO receiver produces smaller noises than the GNOS GPS RO receiver”) Based on this sentence, it looks like the BDS receiver is different from the GPS receiver. Is it so, or is it a GPS-only  VS a GPS-and-BDS receiver?

Ln 186: It is mentioned that the spikes have been reduced in the latest version of the Fengyun data. This is very good, and some description of how this result has been achieved and possibly a figure illustrating it would be very nice.

Figure 1, panel (c): It is rather unusual to have more rising than setting occultations. Can you double-check that the data is correct? If this is the case, please comment on this unexpected asymmetry.

Ln 303: Please provide a description of how you obtain the statistically optimized results. Are you using the ROPP for this?

Ln 381/382: You mention that the orbit determination (OD) and clock estimation of the FY3 is of very high quality. This is an important piece of information and it requires at least the references that support it.

To further support the statement that the OD is not the cause of the residual biases and noises, it would be very useful to see figures similar to, e.g., Fig. 2, but where the datasets are split by rising VS setting products. OD errors often show up as rising VS setting biases above ~ 50 km.      

Figures are not of pdf quality, so when zooming they become blurred.

The y-labels of Figure 8 (panels (a) and (b)) are wrong.

Minor comments:

Ln 71: Missing reference “Anthes, 2024”. The correct one is this: https://journals.ametsoc.org/view/journals/bams/105/8/BAMS-D-23-0326.1.xml

In several places the citation style is incorrect. E.g., in ln 79, “Liao et al., 2016b” should be “Liao et al. (2016b)”

Paragraph starting on line 76: This paragraph presents a comprehensive list of literature. However, only for the paper by Liao et al. (2016b) a short description of the results is provided. Please report concise descriptions of the results of the other papers as well.

Ln 94: What is the NOMEX experiment? Do you mean the ROMEX? If so, please note that the data-collection part has already been completed (see reference in the comment to Ln 71 above).

Paragraph ln 135-144: Please provide a brief description of the schemes mentioned here. This would help the reader understand how your approach is more valid and/or relevant for FY3. If it makes no sense to do so because, e.g., they are all empirically based, provide a qualitative description of them.

Ln 153: You are referring to a non-peer-reviewed publication. It’s ok but at least do include the relevant equations.

Ln 157: I wouldn’t use “It is believed” but something like “We assume that if one of the bending anglesx          …”.

Data availability: you indicate that FY3 data comes from the CMA reprocessing campaign and the Metop-C from the ICDRs. Is there an official way to access the CMA-reprocessed data? Could you indicate where the ICDRs are available?

Edits/Language

Ln 21: Substitute “which are about” with “at about”

Ln 24: Consider shortening “required to improve the quality issue for improving” to just “for improving”

Ln 30: Substitute “As propagating” with “While propagating”

Ln 31: Not sure what “formulated” here means

Ln 33: By “of can” do you mean “of water wapour”?

Ln 35: “2022” should be “2002”

Ln 36: Remove “to be used”

Ln 39: “all weather” should be “all-weather”

Ln 42: “system” should be plural

Ln 44: Substitute “In the meanwhile” with “Meanwhile”

Ln 45: Substitute "detecting” with “detection”

Ln 47: “and also tropical cyclones” is missing a verb or noun (e.g., “detection”, “identification”)

Ln 70: Remove “few” from “In recent few years”

Ln 70: Remove comma after “(ROMEX)”

Ln 71: Substitute “of three months’ period” with “over a three-month period”

Ln 74: Remove “improving”

Ln 76: Either “in stratospheric regions” or “in the stratospheric region”

Ln 77: “bending angles” should be “bending angles”

Ln 78: Substitute “There are current a lot of work” with “Several works”

Ln  87: “a couple of reports” is informal. Use instead “two”

Ln 87: Remove “in” from “in analysing”

Ln 89: “i.e.,” should be “e.g.,”

Ln 90/91: Consider rewriting the sentence as: “Unlike the case of statistical optimization and 1dVar (Li et al., 2013, 2019), the retrieval of bending angles is not influenced by background models”

Ln 92: “are useful” should be “is useful”

Ln 92: Repetition: substitute the second instance of “understanding” with “assessing”

Ln 92: “subsequent retrieved” should be “subsequently retrieved”

Ln 96: “examination” should be “examining”

Ln 97: “subsequent retrieved” should be “subsequently retrieved”

Ln 98: Please list both parties of this joint work, not only CMA.

Ln 148: Remove “: QF1, QF2, and QF3 are used to detect outliers”, since it’s a repetition of the first part of the sentence.

Ln 161: “exceed threshold” should be “exceeds the threshold”

Ln 161-163: Please consider rephrasing as: “QF0 indicates a profile of good quality, i.e., where no quality issues have been detected. QF8 indicates that at least one of the seven quality flags has a non-zero value.”

Ln 176: “observations” should probably be “latitudinal bands” or something similar.

Ln 182: “largest errors” should be “the largest errors”

Ln 213: “also include quality” should be “also includes the quality”

Ln 214: “set a strict criteria” should be “set as a strict criteria”

Ln 214: “solely use” should be “solely using”

Ln 255: “altitude” should be “latitude”

Ln 286: “are mainly comes” should be "mainly come” (or “are mainly coming”)

Ln 287: “suggest a positive” should be “suggests positive”

Ln 288: “data are used” should be “data used”

Ln 313: “sources” should be “source”

Ln 362: “to 15%” should be “15%” (two instances on this line)

Ln 364/365: “biases are around” should be “biases around” (two instances)

Ln 376: “were given” should be “given”

Review of “Quality aspects of Fengyun3 D/E radio occultation bending angle products” by Li et alThe manuscript presents an analysis of FY3 D/E bending angles through a comparison with ERA5 and MetOp observations. After applying quality control, the FY3 D/E results are found to be generally consistent with MetOp data below ~40 km. At high altitudes the FY3 D/E observations exhibit larger biases and noise. The results are clearly presented, illustrating the overall quality of the FY3 D/E data after application of quality control procedures. The overall topic is suitable for publication in AMT, and I recommend the paper for publication following revisions to address some aspects of the text that are unclear. Specific comments are provided below.

Major Comments:

1. The comparisons are done against ERA5. The assimilation of RO observations in ERA5 could potentially impact the results. It is recommended that the authors clarify if the FY3 D/E data are assimilated in ERA5. The fact that the MetOp data are assimilated in ERA5 should also be stated in the text. Furthermore, the potential impact of the assimilation of these data in ERA5 on the results should be clarified in the text.

2. In line 186, the authors state that the spikes that appear in the data “have been reduced in the latest version of Fengyun data.” It would be beneficial to include some additional details on what was changed in the data processing to address this issue.

3. One of the conclusions based on the quality control is that MetOp bending angles have minimal quality issues, and that this is partly due to “strict internal quality control system integrated into the ROPP software” (lines 216-217 and 358). It would be useful to include additional details in terms of what is meant by this statement. Does this mean that the poor quality data were already removed in the processing?

Minor Comments:

1. Line 33: The statement “where the existence of can be neglected” is missing a word.

2. Line 63: “SPIRE” should be “Spire” (it is not an acronym).

3. Lines 78-79: The statement “There are current a lot of work…” should be revised as it is grammatically incorrect.

4. Line 94: What is “NOMEX”?

5. Lines 320 and 323: Should “K” be “%”?

6. Line 348: “empirically analysis of” should be “empirical analysis of”