Remote Estimation of the Particulate Phosphorus Concentrations in Inland Water Bodies: A Case Study in Hongze Lake

Round 1

Reviewer 1 Report

This manuscript mainly constructed a new semi-analytical algorithm to estimate particulate phosphorus (PP) concentrations in Hongze Lake. Moreover, a modeling process for building a remote sensing estimation model of PP concentration was proposed for broadband sensors. And put forward model selection criteria according to the band settings of different sensors. The article drawn some meaningful conclusions. Overall, the research theme of this paper well fits the scope of Remote Sensing. Reviewer appreciates all of the author's efforts in the manuscript. The paper is easy to read in general, and the model and results are solid. However, some questions are still needed to be answered before the manuscript could be published in Remote Sensing.

Major comments

(1)    In the section of Keywords, “total suspended matter” and “driving factors” driving factors do not match the full text and need further verification and modification.

(2)    In section 4.1, the paragraph from lines 363 to 373, this section introduces the response relationship between PP and water quality parameters in different lakes, and references should be added to prove it.

(3)    In the model construction, for example, the three-band algorithm is used, but there are no references. The same problems still exist in other parts of the paper. It is suggested to add references to some cited conclusions and methods in the whole paper.

Minor Comments

(1)    The serial numbers behind the formulas in the text should be aligned

(2)    In the abstract, line 22, the a_t should be changed to a_p.

(3)    Line 275, aph should be changed to a_ph , the format needs further review and modification.

(4)    Line 288, The formula format needs to be modified.

(5)    Line 341, R2 should be changed to R², further verification is required in the full text.

(6)    Line 386-387, “the model accuracy” should be deleted.

(7)    Line 414-415, the Medium-resolution Imaging Spectrometer should be deleted.  

(8)    The full text of the formula size and style needs to be unified.

Author Response

We have made a major revision according your suggestions and comments. The specific response can be found in the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

COMMENTS

to manuscript remotesensing-1836976 “Remote estimation of the particulate phosphorus concentrations in inland water bodies: a case study in Hongze Lake“ by Chenggong Du et al.

Monitoring of particulate phosphorous (PP) concentration is important to ensure water quality protection in any fresh-water lake. The authors focused on investigating PP in Hongze Lake in China. The triple objective of the study included a) conducting in-situ measurements and creating empirical models of PP concentration; b) adaptation of the created empirical PP models to available satellite images; and c) analysis of spatial distribution of PP concentration in Hongze Lake using satellite images. Such a study is of practical importance, as the obtained results help to improve monitoring of spatial distribution of PP concentration in the lake and, consequently, prevent lake eutrophication.

There are some points, however, which require clarification. Below are my specific comments.

1. Introduction:  It is desirable to discuss day-to-day/month-to-month/year-to-year variability of total and, possibly, particulate phosphorus concentrations in Hongze Lake, based on previous publications.

2. Lines 145 – 147: My concern is about the limited number of only four days when water quality tests were conducted. Please specify explicitly the number of days with measurements, as well as their dates in the proper format, and how many measurements were collected in each day. This information should be clearly stated.

3. What are the hydrological and meteorological criteria for the selection of 18 September and 20 November 2020 in order to represent PP concentration in autumn, and 19 April and 21 March 2020 to represents PP concentration in spring? Please clarify in the text. Were the hydrological and meteorological conditions on those four days exceptional or regular? Please specify.

4. What about water quality parameters in summer and in winter, when measurements were not conducted? Are they the same as in other seasons or maybe totally different? Please explain.

5. Table 1. What were the criteria for the selection of 16 January 2022 to verify the accuracy of empirical PP models? It was a completely different day, month, and year compared to measurements. The hydrological and meteorological conditions on 16 January 2022 did not correspond to those in the specified dates, when in-situ measurements were conducted: in spring and autumn in the year 2020. So how was it possible to verify the accuracy of empirical PP models? Please explain.

6. Line 218. Fig. 1a should be updated with Fig. 2a.

7. Line 220. Fig. 1b should be updated with Fig. 2b.

8. Figure 2b. Please specify in the figure captions what the various colours designate.

9. Line 278:  What does the expression “the 1:1 line” mean?

10. Figure 4b: To confirm the relationships between the measured and estimated PP concentrations, it is essential to display a correlation coefficient between these parameters. MAPE and RMSE are not sufficient. Please add a correlation coefficient to Fig. 4b.

11. Figures 5b and 7b. To confirm the correspondence between the measured PP concentration and that estimated from Sentinel-3/ Landsat-9 satellite data, a correlation coefficient should be added to Fig. 5 b and Fig. 7b.

Author Response

We have made a full revision by considering carefully your comments. The details of the response can be found in the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The authors addressed all of my comments. The manuscript can be accepted in the present form.