Monitoring Surface Displacement of a Deep-Seated Landslide by a Low-Cost and near Real-Time GNSS System

Round 1

Reviewer 1 Report

The paper monitors surface movements of a landslide by a newly developed low-cost and near real-time GNSS monitoring system. The papers presents an interesting subject and is generally well-written. The paper however may be improved if (a) a cross-section of the landslide is given together with relevant cross-sectional soil/rock profile and water table depth and (b) stability analysis is performed to back-estimate the mobilized soil/rock strength (in a  similar manner as to that performed e.g. by Di et al., 2016). If the above cannot be performed within the scope of the present paper, they may be described in the discussion section as future beneficial work.

 

REFERENCE

 

Di B, Stamatopoulos C. A, Dandoulaki M., Stavrogiannopoulou E., Zhang M., Bampina P. 2017. A method predicting the earthquake-induced landslide risk by back analyses of past landslides and its application in the region of the Wenchuan 12/5/2008 earthquake, Natural hazards, 85 (2), 903-927

Author Response

LINE	REVIEWER	REVIEW	AUTHORS’ COMENT
141	1	The paper may be improved if a cross-section of the landslide is given together with relevant cross-sectional soil/rock profile and water table depth	A cross-section of the landslide has been added as Figure 2.
/	1	The paper however may be improved stability analysis is performed to back-estimate the mobilized soil/rock strength (in a similar manner as to that performed e.g. by Di et al., 2016).	Stability analyses are a part of the ongoing research in the area; however, the authors believe their presentation would be beyond the goals of this paper.

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript is very interesting, it is well described and the conclusions are well supported by results. The scientific novelty is small, but the information provided regarding what we can achieve with the new low-cost GNSS measurements could deserve a publication on Remote Sensing journal.

Following on the low-cost aspect, did the Authors check if inSAR interferometry could be of any help in the selected area? there are publications that use InSAR to monitor deep-seated landslides. Here an example.

https://pubs.geoscienceworld.org/gsa/geology/article-abstract/39/6/527/130578/Analysis-of-large-seismically-induced?redirectedFrom=fulltext

I think the advantage of InSAR is to have much more points spatially distributed. Moreover, there are constellations, such as Sentinel-1, that are free of charge with a time sampling of 6 days. Of course the disadvantage could be the vegetation, the orientation of the landslide with respect to the line of sign of the satellite, etc...Could you please discuss a bit more this aspect? 

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

September 2, 2020

Dear Editor, dear Authors:

This manuscript entitled “Monitoring surface movements of a deep-seated landslide by a newly developed low-cost and near real-time GNSS monitoring system” presents results from surface movement monitoring of a deep-seated landslide by a low-cost GNSS monitoring system. The topic fits the scope of the Journal and might meet the interest of the scientific community. However, in its actual form, the manuscript is not ready for publication and needs substantial improvements before to be reconsidered for publication. Specific comments are reported below:

Additional comments:

• Even if I am not an English-native speaker, I would recommend an English edit to improve sentence structure and terminology. The text is difficult to read at some points and several sentences need to be modified.
• The introduction does not provide enough information about the general need for landslide monitoring and recently developed low-cost systems. For instance, Guerriero et al. (2017) developed an arduino-based low cost system for landslide monitoring (Brief Communication: A low cost Arduino®-based wire extensometer for earth flow monitoring, Natural Hazards and Earth System Sciences), Ruzza et al. (2020) recently developed a medium to high performance multi-module fixed inclinometer for continuous monitoring of landslides. In my opinion you should add such information to better contextualize your research.
• The objective of the paper is not clear from the text and should be better explained. The Authors present (and discuss) on one hand the system and evaluate its performance on the basis of existing data, and on the other hand the kinematics of the landslide and relation between movement velocity and rainfall. These aspects should be better clarified improving the focus of the manuscript that in its actual form appears too general influencing its final contribution to both the knowledge of the system and of the landslide.
• To present and discuss system performance, it should be described in details providing all of the constructive elements and code functions. The Authors would reserve some information for a forthcoming paper describing the system and its operational approach in GNSS network. In my opinion these aspects have to be known to have a comprehensive overview of the monitoring network, so that, I would suggest either to add this information to the manuscript or to proceed first with the manuscript describing the system and subsequently to present and discuss results from field application.
• A major concern is related to the lack of a well-defined comprehensive landslide model able to guide installation site determination and data interpretation in the context of landslide mechanism and deformational styles. Most of the interpretations, related to obtained displacement data, discussed in the text seems to be not well correlated to the considered landslide model and not consistent with a identified movement mechanism. While the Authors generally refer to a deep-seated landslide, data acquired in its lower part seems to indicate the existence of further processes acting above the deep-seated slide. In addition, the landslide is not well defined in terms of source, transport and deposition zone nor in terms of surface deformation (i.e. zone of stretching, neutral and shortening). The interpretation of the relation between surface movement and rainfall event seems to be not fully convincing confirming the need for a better model.
• The structure of the manuscript has to be improved. Section 4 should be included in the method section and a further subsection describing the analysis of the relation between movement and rainfall is needed.
• The quality of the figure is not excellent and displacement data require error bars to better understand data.
• It would be important to know the final cost of the system in comparison with that of commercial system.
• Additional comments and suggestions are reported in the attached annotated manuscript.

Best regards.

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

October 8, 2020

Dear Editor, dear Authors:

The manuscript entitled "Monitoring surface displacement of a deep-seated landslide by a low-cost and near real-time GNSS system" has been reviewed according to reviewers comments and appears to be improved from the first version. On this basis, in my opinion, it can be suitable for publication in Remote Sensing.

Best regards.