Simultaneous Retrieval of Corn Growth Status and Soil Water Content Based on One GNSS Antenna
Round 1
Reviewer 1 Report (Previous Reviewer 3)
The manuscript focuses on the agricultural remote sensing application of GNSS-IR. It proposes an algorithm based on empirical mode decomposition (EMD) and the difference in spectrum peak power to decompose and distinguish GNSS signals reflected by soil surface or corn canopy for simultaneous retrieval of corn growth status and soil water content that shows the credibility of the present work. The analysis done in this manuscript is impressive and worthy from an application point of view. As per my review, the manuscript has been improved by incorporating all the previous comments compared to the previous version.
The authors have given utmost effort in improving the manuscript and I must recommend acceptance of the manuscript in its present form without any further comments.
Author Response
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Reviewer 2 Report (New Reviewer)
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Round 2
Reviewer 2 Report (New Reviewer)
The authors have incorporated into the manuscript all suggestions provided by this reviewer. The manuscript has been greatly improved. I congratulate you for the end result.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
There are still many uncertainties within this manuscript. I'm sorry to inform that this paper is not suitable for publication in MDPI RS.
Author Response
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Reviewer 2 Report
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Reviewer 3 Report
The manuscript proposes an algorithm based on empirical mode decomposition (EMD) and the difference in spectrum peak power to decompose and distinguish GNSS signals reflected by soil surface or corn canopy for simultaneous retrieval of corn growth status and soil water content. Although the analysis is done in this manuscript is impressive, I have a few concerns that the authors are expected to implement in the succeeding version of their manuscript.
Line 16-17 The root means square error (RMSE) units are incorrect
The authors used an emerging technique for simultaneous retrieval of corn growth status and soil water content, however, a brief description on the technology used is missing in the introduction part. The authors are expected to provide a few lines on the additional emerging application in GNSS- Interferometric Reflectometry in sea surface height, water depth, soil moisture, crop growth etc. along with its wide implementation in positioning, navigation, timing, tropospheric water vapor, ionospheric delay and scintillation applications and so on. I also suggest the authors add the basic principle on which the present study relies “The reflected signal oscillates after interfering with the multipath surface and can be noted in terms of signal-to-noise ratio (SNR) measurements. The investigation of the SNR amplitude oscillations provides signatures of direct and reflected signals from which the components of reflectance due to soil moisture and crops heights can be discriminated. I suggest the authors provide a brief note at the beginning of the introduction rather than explicitly stating the past reports related to the current study. Few basic things about the GNSS-IR capability are discussed in Ansari et al 2022 (https://doi.org/10.1038/s41598-022-25994-6)
VMD is more efficient method than the EMD algorithm, since it is capable of decomposing given signal into lesser modes with non-recursive iteration. The authors should refer and cite Ansari et al 2022 (https://doi.org/10.1038/s41598-022-25994-6) that discusses the implementation of VMD algorithm with GNSS-R datasets to decompose the original time series into a different number of distinct intrinsic mode functions. There are also other methods like singular spectrum analysis (SSA) (refer and cite Dabbakuti et al. 2021 (https://doi.org/10.1016/j.actaastro.2020.08.034 )that extract the trends of process signals using the eigenvalues of trajectory matrices and used by many researchers in GNSS datasets for retrieving specific variability. Although the authors cannot use all methods for the present study, they should articulate the different existing methods as above to acknowledge the works done using the related methods used in this study.
The other point I would like to ask does the authors use GNSS signals from different constellations or only the GPS signals? Please specify and replace the term accordingly.
Reference items 10, 12, 27, 28 and 29 are missing volume and page numbers. The authors may verify other reference items which I might have skipped during review.
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Reviewer 4 Report
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Reviewer 5 Report
The author studied the inversion of soil moisture and crop growth state under the condition of crop cover by using GNSS reflection signal. They used the spectral characteristics of different reflectors to distinguish reflected signals from corn or soil. This method is novel and worth studying. This manuscript could be accepted with a revision.
1. Abstract: empirical mode decomposition (EMD), if the noun is not used in the future, do not abbreviate it.
2. Line 99 ‘Usually, we ignore the difference and assume that ’, please provide the basis for your hypothesis.
3. Line 148 ‘The Fresnel reflectivity coefficients of RHCP and LHCP can be calculated by’, please introduce the Fresnel reflection zone.
4. Line 180 Which system does PRN stand for? Is it a satellite selected from all systems or only GPS system? After satellite selection, it should be stated that i is the selected satellite PRN, not 1-32.
5. Line 199 the altitude should be described as orthometric.
6. Please add the in-situ measurement methods of soil moisture, vegetation height and vegetation moisture content.
7. Figure11, add the corresponding VWC of corn leaf in the legend.
8. Figure12, add the description of PRN2 error bar
Author Response
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Round 2
Reviewer 4 Report
The authors answered to all the queries in an exhaustive manner. T
It is worth publishing the new version of the paper in Remote Sensing journal
