Evaluation of Discharge Measurement Uncertainty of a Surface Image Velocimeter

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this study, based on the GUM standard, formulas for calculating the uncertainty of surface velocity, depth-averaged velocity, and discharge were developed. Furthermore, using the standard uncertainty evaluation results, the velocity uncertainty of surface velocity and depth-averaged velocity, and the discharge measurement uncertainty of the surface image velocimeter were evaluated. It is believed that the velocity and discharge measurement uncertainty framework for surface image velocimeters and the uncertainty analysis results presented in this study can provide the reliability of discharge measurement results obtained from surface image velocimeters, thereby contributing to the wider adoption of surface image velocimeters. The reviewer would like to propose the following comments based on the contents of the manuscript.

1. In line 213, the ground sampling distance is the physical size (in meters) of one pixel in the image. If the image coordinates and physical coordinates of known reference points are obtained through reference point surveying, the physical coordinates of all pixel points within the image can be determined. How does the uncertainty in ground sampling distance vary with river size and camera distance, and why does it become negligible in these cases?
2. In line 330, Based on the standard uncertainty evaluation results for each factor, we intend to apply the GUM standard, as described in the previous section, to an actual river to calculate the discharge measurement uncertainty of a surface image velocimeter. Why was the Andong River Experiment Center specifically chosen for evaluating the uncertainty in discharge measurement using surface image velocimetry, and how does its channel design ensure representativeness for small rivers under Korean law?
3. In line 368, Furthermore, the discharge measurement uncertainty for each measurement point and the overall data were used to evaluate the combined standard uncertainty of the discharge measurement. How were the specific uncertainty contributions (0.5% from the mid-section method, 0.0% from transverse verticals, and 2.7% from measurement conditions) quantified, and why does the transverse measurement verticals contribute zero uncertainty despite potential spatial sampling limitations?
4. In line 406, Can you provide the specific formulas developed for calculating the measurement uncertainty of surface velocity, depth-averaged velocity, and discharge, and explain how the relationships between these variables were mathematically incorporated into the uncertainty evaluation method?

 

Author Response

Please refer to the attached file for the answer.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript presents a procedure for the uncertainty quantification of discharge measurements based on surface image velocimeters. The work describes the main sources of uncertainty and then analyzes their typical order of magnitude using river experiments as a case study. The proposed methodology stems from previous techniques based on the GUM standard.

The object of the work and the proposed uncertainty quantification approach are both suitable for publication on Water. To the best of the present reviewer's knowledge, the technique is quite up-to-date, as well as the experimental approach. The present reviewer recommends the article for publication whether the following (minor) issues are properly addressed:

- the paper is full of acronyms, which are mainly defined in the initial section. The present reviewer suggests to include a list of symbols/acronyms in the revised version of the manuscript to improve readability

- the paper writing style is a bit convoluted in some points. The present reviewer recommend to improve the style of the manuscript by reducing the length of the sentences and rephrasing them. In particular, the abstract section must be improved.

Comments on the Quality of English Language

See "Comments and Suggestion to Authors". The manuscript writing style must be improved before publication.

Author Response

Please refer to the attached file for the answer.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The revisions are satisfactory to this reviewer. The manuscript is recommended for publication after spell check and equation editing.