Monitoring Subsidence in Urban Area by PSInSAR: A Case Study of Abbottabad City, Northern Pakistan

Round 1

Reviewer 1 Report

The authors propose a study of the ground displacements of the region of Abbottabab city using PSInSAR data.  The PSInSAR processing is well explained, but the geological setting and the interpretation of the results have to be further improved to convince me. Here are some comments that should be corrected.

Line 95-100 and figure 2: the basement lithology and the soil should be longer explained. Indeed, these two parameters control the ground subsidence depending on the process involved in the vertical motion of the ground. The “geological” map of the figure 2 is not a real geological map, but it is a patchwork of colours with some ugly patterns. The coordinate labels are too small.

 Figure 4: the size of the x-axis label is too small. It is impossible to read the labels.

 Lines 178-182: a geomorphological map is mentioned. Where is it? What do you need a geomorphological information to interpret the results? How geological and geomorphological data can help to interpret the PSInSAR results?

 Lines 184-195: this section is not at the good place: it should be split and moved into the general setting and processing sections.

 Results section

Line 122: how do the authors choose the PS points? Please justify this choice. Why there is no PS point outside the city?

Line 227: the authors defined a subsidence domain with a red polygon. However, the polygon includes positive values in blue, i.e. with an uplift!  The subsiding domain should be redefined.

Lines: 229-234: the authors describe the result in in terms of cumulative displacements with units in mm/year, i.e a rate! What is right? Please check. By consequence it is impossible to evaluate the quality of the results display on the figure and comment in the text.

 The figure 7A, 7B, 8A, 8B have different horizontal and vertical scales and too small police for the axis labels. Therefore, I don’t think that the given horizontal scale is correct for the vertical direction. I don’t understand the differences between the figure 7 and 8, except for the location of the PS points. There is also a misfit between the geographical coordinates the maps. Please these two maps have to be redrawn. That’s a pity because it is THE results of this study. 

 The subsidence results where display with a set of maps (figures 7, 8, 11, 12) with curious color scale. What is the interval of the color scale? Linear, logarithmic? It is impossible to compare the results shown of these maps with subsidence profiles associated to the maps. For instance, on the figure 12, the profile at right displays negative values, while the profile of the map at left crosses positive values in green-blue!

The profiles cross subsidence areas with no values (in grey scale on map). Why are there subsidence values on the profile? (see figure 11, for instance)

Line 241: it is impossible to follow the comments about the subsidence of Abbottabad city in the text and on the map 10 because the town is not drawn.

Line 260: rate or cumulative displacement, please check.

Discussion section

The main result of this study consists of a subsidence of the town. The authors propose that it results in an over extraction of water in the aquifer. This process is possible but it is not the only process that can generate such a subsidence. An overloading generated by the town building or the tectonic process can generate also such a subsidence. The authors should add some independent data to confirm their interpretation such the water level in the aquifer. If the subsidence is induced by the intense withdrawal of the aquifer, does this subsidence rate decrease during the rainy season? Indeed, when the aquifer is fed by the rain, the water extraction can be partially compensated by the precipitations.

There is a subsidence of the town and an uplift outside the town. What does it mean? Is there a recharge of the aquifer outside the town, if we follow the proposed interpretation? The distribution of the vertical displacements with subsiding and uplifting domains is also compatible with a local loading. How you can reject this interpretation?

   To conclude. This study displays an interesting technical study of the ground displacements in the area of Abbottabad city. The processing is good but the results and the interpretation are very badly presented and justified. The quality of figures is also bad. Thus, I cannot accept this manuscript in such a form, I strongly recommend to reject it.

Author Response

Thank you for your kind suggestions and recommendations regarding my manuscript. It has been modified further according to suggestions given by reviewers.

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript "Monitoring Subsidence in Urban Area by PSInSAR: A Case Study of Abbottabad City, Northern Pakistan" is submitted as a research article to Remote Sensing (MDPI). Although the manuscript is interesting, the methods and data are not novel but show an interesting application of DInSAR using coarse resolution imagery on an urban area containing several engineering structures and elements. My concern is the timeframe from 2017 to 2019 without giving proper details or hints for what happens in 2020 or even 2021 or current trends.

Moreover, no sentinel-1 SAR scene is shown, and since urban areas present buildings and constructions besides some structural elements (fences, bridges, pole, etc) the flight direction could be important information. Layover is also not discussed either. The absence of ground pictures and GNSS measurements also weakened results and even not mentioned to be conducted in future research.

The research development seems to be quite thorough, but the introduction still doesn't provide a proper state of the art of research and does not cite pertinent research already published in the literature on the same subject. Additionally, the novelty aspect, which seems to be the study area, is not well justified, requiring another round of review or even resubmission. I also noticed some disorganization in the current version of the manuscript what makes it especially difficult to understand and to follow the entire processing chain (check comments L103, L110, L123, L125, etc).

In summary, the current status doesn't allow to have a full confidence in the results and does not allow reproducible research. The main text and content must be organized to reach the scientific standard of a research article. Results could be improved and discussion could be enhanced by comparing their results with other similar research outcomes. The conclusion could be shortened and stated in a broader context. The absence of recommendations is also something that weakened the current version of the paper. The quality of the figures must also be improved in the revised version of the manuscript. After printing it using a B&W laser printer, some numbers and legends were impossible to read. This must be fixed accordingly. 

Other concerns

L17: usually overexploited;

L24: check pertinence of word "rates" and also check values for a given year -30mm/year for 2017 and -85mm/year for 2018, and what about 2019 and 2020? The values are not consistent and the units must be revised;

L26: is this trend noticeable with urban constructions? some implications?

L28 although low values, please indicate them;

L35: the introduction must be more generic mentioning structure monitoring with InSAR, DInSAR, etc; PSI technics and the SAR imagery principle are not well introduced as well;

L55: please consider adding some more references to justify worldwide areas;

L66: similar research has been conducted in other areas worldwide and could be mentioned here too;

L76: describe shortly importance of evaluating both descending and ascending tracks since this could be used as a novel aspect;

L78: justify the novelty about the study area and the absence of similar studies in this study area using other techniques or similar techniques with Sentinel-1;

L83: remove redundancy terms "proposed study area is located" since you repeated in the sentence above. Just cite the coordinates between round brackets after mentioning the city name;

L94: please improve the quality of the map using a proper GIS software;

L95: please enhance the quality of the map. The coordinate numbers are too small and the legend is not legible. Additionally, it is important to cite the source and also to link the results afterward with this map. I would even print the boundaries of the Sentinel-1 footprint here (and also in Figure 1);

L103: here there is quite a reasonable number of misunderstandings. Usually, we cite here acquisition mode, processing level of the SAR data and this appears partially on L135;

L110: what do you mean by using the term "a single acquisition"? It would be better to mention the temporal resolution of the given system;

L120: please increase the size of this figure and link it with the subsections numbers/ids;

L120: please consider making a methodological flowchart for the entire manuscript and not just for SARPROZ;

L121-123: some of the terms are not in the flowchart;

L122: explain better stability index;

L123: I would prefer to explain in section 3.1 and please explain the meaning of SRTM and DEM and also its spatial resolution (what you somehow did in L149);

L125: what do you mean with APS estimation? You first mention it in L136, but you did not explain it at all;

L128: check the quality of the figures (no need to include the title above the figure and impossible to read the dates in X-axis;

L129-130: please rewrite the sentence;

L137: which polarization? which orbit configuration? besides placing spatial coverage in Figures 1 and 2 (ascending and descending tracks) a data table should also be provided with SAR geometry parameters;

L140-145: did you check for proper orbit info files? TOPS, POEORB, RESORB could be mentioned here;

L145: how is coregistration is performed?

L147: how you get them?

L149: 1 arcsec that was reprojected to UTM (~30m)? with version? where?

L150: explain;

L153: detail;

L178: geomorphological map? where you presented it?

L182: no field research and inspection? or even local reports or GNSS measurements? a presentation of ground pictures and GNSS data helps in gaining confidence data;

L184-187: these lines seem to be methods or even better in the study area description;

L195: please justify with references;

L202: are the results still experimental?

L205: please indicate timeframe and sensor; also increase the size for better visualization;

Figure 6: please think in a better way of presenting such results since X-axis is confusing and no link is established with a transect or other geometric figure leading to misunderstandings; it seems that they represent PS points (L215) but no idea where and logical way;

Figure7: which optical image is in the background? additionally, please explain the timeframe used for the SAR dataset in both tracks;

L222: why these are selected? justify and explain which elements they represent in the ground and when possible either a picture or description;

L234: seems a definition already explained before;

Figure9: please include a year as additional info on X-axis;

Figures 11 and 12: please consider explaining the circles and please use arrows to indicate features in graphics on the right side;

L262: the discussion section could bring some more references; and bring some discussion about future research perspectives in i) remote sensing applications and perspectives in terms of continuous monitoring systems, mainly for security issues and also insurance applications; ii) sustainability and social aspects;

L269: are there some numbers?

L299: bring all minor findings into a broader context, and do not bring info that was not previously discussed before;

L337: please use a proper reference system because most of your references are wrong; the references are not following the guidelines at all;

Thank you for the opportunity to evaluate this paper. I encourage the authors to resubmit their research again.

Author Response

Thank you for your kind suggestions and comments. I have modified the new manuscript according to new your suggestion.

Author Response File: Author Response.docx

Reviewer 3 Report

The aim of the paper entitled Monitoring Subsidence in Urban Area by PSInSAR: A Case Study of Abbottabad City, Northern Pakistan is to present the results of evaluation the capability of PSInSAR technique for ground subsidence analysis in an urban area. Overall paper is well prepared but some aspects need improvement:

1. please indicate in the abstract that the issue at stake does not only concern Pakistan, but is a global issue
2. please improve the quality of Figure 2
3. the geological description is too short
4. there is a lack of any hydrogeological settings decription
5. please describe in particular used methodology 
6. what is the accuracy of used methods?
7. have other factors causing subsidence been considered?

Author Response

Thank you for your suggestions and comments, I have modified the new manuscript accordingly.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The research entitled "Monitoring Subsidence in Urban Area by PSInSAR: A Case Study of Abbottabad City, Northern Pakistan" is a resubmitted manuscript. I am pleased to see that the manuscript improved significantly, with new sentences clarifying the methodology better. I also notice that the addition of some figures highlighted the research. However, some typos are found and must be corrected (most probably by typing the new sentences and keeping the track-changes on). Additionally, some final art is still necessary to better use circles and arrows in some figures to improve esthetic. The use of MS-Excel for figures is not recommend. I would better suggest using R or some other software make the figures more presentable. I would also recommend that some local pictures are included as complementary material at the end of the paper. In summary, both comments and concerns were adequately addressed. I am confident that the current version of the paper can be recommended now for publication. I would only suggest if they revise the typos and improve the figures for a quick and speedy minor review.

Author Response

Thank you for your kind suggestions, most of the sections of the manuscript has been revised and modified according to suggestion and comments.

Author Response File: Author Response.docx

Reviewer 3 Report

Authors have improved the manuscript. It can be published.

Author Response

Thank you for your suggestion and most of the sections of the new manuscript has been modified.