Field Radiometric Calibration of a Micro-Spectrometer Based on Remote Sensing of Plateau Inland Water Colors
, Junsheng Li 1,2 and Libing Wang 1,2Round 1
Reviewer 1 Report
This paper performed the field radiometric calibration of a Micro-spectrometer and it was used to detect the reflectance (Rrs) of water bodies. In radiometric calibration parts, the authors performed sensitivity about integration time, fiber core diameter, and diffuse reflector/target cloth. Finally, the calibrated micro-spectrometer and Trios were used to measure Rrs of Qinghai Lake and Golmud City River. The observed Rrs via different instruments agreed well with each other, achieving a high correlation coefficient of 0.99. Overall, this paper is well-organized and Intelligible, and I recommend publication with reference to the following comments.
[1] Line 92-93, the authors introduced 3 radiometric calibration methods and chose field diffuse reflector calibration method due to its simplicity finally. However, the authors didn’t compare the calibration accuracy of field diffuse reflector calibration and laboratory integrating sphere calibration.
[2] Line 164, the authors took advantage of cubic spline interpolation method to resample the spectrometer data. The authors should explain why he choose the cubic spline method here. A sensitivity test with other interpolation methods should be provided, even put it in the appendix.
[3] Line 177-178, the models of different fibers should be introduced in detail.
[4] L183-L226, the authors utilized the SNRs to evaluate the observation effects under different integration times. However, the relationship between SNRs and observed Rrs were unclear, hence I recommend the authors try to determine the integral time via the retrieved Rrs directly.
[5] L206-207, the dark current signals are tightly related to the observation temperature. The test about integral time should be performed under a constant temperature.
[6] L196-198, what did the numbers in the brackets indicate?
[7] L263-L264, how could the authors attribute the larger error at 760nm to water vapor absorption?
[8] A detailed error analysis of Rrs was important for readers to repeat this method.
[9] Line 132 & Discussion section, in my opinion, the Dark current and Offset spectra should be corrected in radiance and irradiance before calculating Rrs via Equation (1).
Author Response
For detailed responses to comments, please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This manuscript proposes the use of a micro-spectrometer to determine the remote-sensing reflectance, which can be used in unmanned scenarios. Although the English in this paper is fine, I found the descriptions of the above-water and proposed methods unclear. They should be expanded to include more diagrams and figures instead of only relying on a written description. Some more explanation of the operation of a microspectrometer would be helpful. Also some more intuitive explanations of the equations in the manuscript, e.g., Equation (8), would be helpful And for example, on lines 254-255, the authors state that they have made the Gains and Offsets for two fibre types available without providing the web address they could be found in the text of the manuscript. If these points were to be addressed, then I believe the manuscript could be considered for publication.
Author Response
For detailed responses to comments, please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors have spent much effort to improve the manuscript, which is now in much better shape. In my opinion, it is suitable for publication in Applied Science.
Author Response
We sincerely appreciate your comments and suggestions regarding our manuscript.
Reviewer 2 Report
The authors have addressed the points I raised in the previous round. There are some new errors that have been introduced. The caption of Figure A-1 currently reads "Conceptual view of the micro-spectrometer carrying an unmanned ship to collect water body spectrum". It should instead read "Conceptual view of the unmanned ship carrying a micro-spectrometer to collect water body spectrum". It would also be better for the new Appendix to have a title.
Author Response
We sincerely appreciate your comments and suggestions regarding our manuscript. You are indeed right about the title of Figure A-1. We take the advice you gave us. Figure A-1 is titled "Conceptual view of the unmanned ship carrying a micro-spectrometer to collect water body spectrum". we used one of the editing services listed at https://www.mdpi.com/authors/english or have your manuscript checked by a native English-speaking colleague. The revised content is as follows:
Fig A-1 Conceptual view of the unmanned ship carrying a micro-spectrometer to collect water body spectrum, the side view details the angle of measurement of the zenith angle of the three sensors followed for spectrum collection and the top view details the angle of measurement of the azimuth of the three sensors for spectrum collection. （Line 397-400）
