Reconstruction of Annual Glacier Mass Balance from Remote Sensing-Derived Average Glacier-Wide Albedo

Round 1

Reviewer 1 Report

I read this manuscript carefully. The manuscript is quite meticulously done. Everything is so well done.

I have only one small comment that the authors add a section-5.5 that could be named limitations and prospects. Where the current bottleneck of this work is elaborated.

Author Response

Point 1: I read this manuscript carefully. The manuscript is quite meticulously done. Everything is so well done. I have only one small comment that the authors add a section-5.5 that could be named limitations and prospects. Where the current bottleneck of this work is elaborated.

RE: (1) Many thanks for the Reviewer’s suggestion. We have added sub-section 5.5 to discuss the future prospects and limitations of the improved albedo-mass balance (IAMB) method. Please see details in the sub-section 5.5.

(2) In additon, according to the suggestions from other reviewers, we have also made some revisions to improve the manuscript, mainly including: (1) deleting some inconsequential and repeated content in the dataset section; (2) adding a data processing flowchart (now Figure 2 in the revised version) to describe the IAMB method in more detail; (3) rewriting the reasons for choosing average glacier albedo in sub-section 5.4; (4) changing the image resolution from 300 dpi to 600 dpi and (5) correcting grammatical and spelling mistakes in the full text.

Author Response File: Author Response.pdf

Reviewer 2 Report

(1) Brief Summary:

The investigation looks into an interesting research area of estimating the annual glacier mass balance using summer albedo. This is a significant contribution to the presently evolving climate change-related uncertainties.

 

(2) Broad Strength and Weakness:

Pro: The investigation evaluated the use of average summer albedo to calculate annual glacier mass balance.

Con: The authors have not discussed the potential of including satellite SAR data in the absence of optical data.

 

The reviewer would like to thank the authors for this thoughtful manuscript. This work has good potential. The authors are requested to put in some additional efforts to improve the quality of this manuscript. 

 

Introduction 

The authors are requested to elaborate more on the glacier-related disaster and cite the following article that reported a major disaster over the Himalayas, which largely impacted the local human livelihoods. 

-Shugar et al, A massive rock and ice avalanche caused the 2021 disaster at Chamoli, Indian Himalaya, Science, 2021

 

Methodology 

The review would like to know how the authors consider the glacier's thickness and the ice density while calculating the annual mass balance. Moreover, the albedo-based approach might underestimate the mass balance over the debris-covered glaciers. Please discuss further on this.

 

Flowchart

It is difficult to understand the methodology without a flowchart. The authors are requested to provide a flowchart/diagram to illustrate the different steps in the methodology.

 

Radar Satellite-Based Approaches 

The authors have only discussed the advantages of the coarse-resolution optical albedo-based approaches and neglected the possibility of monitoring the high albedo areas of the glaciers with high-resolution SAR satellites and relating it to the glacier annual mass balance. The authors are requested to discuss the contributions of the following articles in this direction and indicate their utility for monitoring cryospheric elements in the absence of optical data. 

-Nagler et al., “Advancement for Snowmelt Monitoring by Means of Sentinel-1 SAR”, Remote Sensing, 2016. 

-Muhuri et al., “Snow cover mapping using polarization fraction variation with temporal RADARSAT-2 C-band full-polarimetric SAR data over the Indian Himalayas”, IEEE JSTARS, 2018. 

-Tsai, Y.L.S., et al., 2019. Remote Sensing of Snow Cover Using Spaceborne SAR: A Review. Remote Sensing.

 

Site Selection

The authors are requested to explain the reason for the selection of the Chotta Shigri glacier for this investigation. This is a relatively narrow glacier as compared to a neighbouring glacier, the Bara Shigri, which offers a relatively larger debris-free area and is beneficial for albedo based approach.

 

Table 1

The authors present datasets with different solar elevation angles. The reviewer would like to know how the authors have normalized the spectral reflectance from different scenes. For example, in Fig. 5 (b) the area seems to be overexposed and it is difficult to distinguish the glacier boundaries due to the snow cover in the surrounding areas. The authors are requested to consider the use of standard glacier inventories to demarcate the boundaries of the glacier.

 

Fig. 4

 

It is difficult to understand this figure and the authors have also presented the dates in a cluttered format. The authors are requested to use a smoothly varying colour bar to indicate the temporal change (dates) and plot the changing albedo along this bar.

 

Author Response

1、(1) Brief Summary:

The investigation looks into an interesting research area of estimating the annual glacier mass balance using summer albedo. This is a significant contribution to the presently evolving climate change-related uncertainties.

(2) Broad Strength and Weakness:

Pro: The investigation evaluated the use of average summer albedo to calculate annual glacier mass balance.

Con: The authors have not discussed the potential of including satellite SAR data in the absence of optical data.

RE: Thanks for the Reviewer’s suggestion. Our improved albedo-mass balance (IAMB) method reconstructed annual glacier mass balance based on the averaged glacier-wide surface albedo in this study. And, glacier surface albedo is generally retrieved from the optical imagery data, such as Landsat, MODIS, AVHRR, AVIRIS, SPOT, and so on (Yue et al., 2017). The SAR data can be utilized for snow cover mapping or snow classification and further to extract snow line, rather than the calculation of glacier albedo. While the snow line information from SAR data may used to estimate glacier mass balance with a method similar to albedo-based mass balance estimation (Rabatel et al., 2016), this is beyond the scope of this manuscript. Therefore, we do not use or discuss the potential of SAR data in our study.

2、The reviewer would like to thank the authors for this thoughtful manuscript. This work has good potential. The authors are requested to put in some additional efforts to improve the quality of this manuscript. 

RE: Many thanks for the Reviewer’s suggestion. We have carefully read this manuscript and made some revisions to it, mainly including: (1) deleting some inconsequential and repeated content in the dataset section; (2) adding a data processing flowchart (Figure 2) to describe the IAMB method in more detail; (3) rewriting the reasons for choosing average glacier albedo in sub-section 5.4; (4) adding the discussions on future prospects and limitations of the IAMB method in sub-section 5.5; (5) changing the image resolution from 300 dpi to 600 dpi and (6) correcting grammatical and spelling mistakes in the full text.

Introduction 

3、The authors are requested to elaborate more on the glacier-related disaster and cite the following article that reported a major disaster over the Himalayas, which largely impacted the local human livelihoods. 

-Shugar et al, A massive rock and ice avalanche caused the 2021 disaster at Chamoli, Indian Himalaya, Science, 2021

RE: Thanks for the Reviewer’s suggestion. We have carefully read this paper and cited it at lines 41-46.

Methodology 

4、The review would like to know how the authors consider the glacier's thickness and the ice density while calculating the annual mass balance. Moreover, the albedo-based approach might underestimate the mass balance over the debris-covered glaciers. Please discuss further on this.

RE: (1) Maybe our unclear descriptions mislead you. The IAMB method reconstructed the annual glacier mass balance based on the mean mass balance (), average summer albedo, as well as the mass balance-albedo gradient (). Please see details in the Figure 2. Additionally, the  used in this study was calculated from the in-situ annual mass balance series, therefore, the glacier's thickness and the ice density are not used and considered here. If  is obtained from the geodetic method, glacier's DEM, thickness and the ice density will be considered for mass balance estimation. We have rephrased the explanation at lines 244-251 in the sub-section 3.4.

(2) Thanks for the Reviewer’s suggestion. We calculated and utilized the average summer albedo except for the debris-covered regions; therefore this albedo-based method can underestimate the mass balance for the debris-covered glaciers. It is one of the method limitations. We added the discussions on this issue in the sub-section 5.5. Please see details at the end of second paragraph in sub-section 5.5.

Flowchart

5、It is difficult to understand the methodology without a flowchart. The authors are requested to provide a flowchart/diagram to illustrate the different steps in the methodology.

RE: Thanks for the Reviewer’s suggestions. We have added a data processing flowchart (now Figure 2 in the revised version) to depict the IAMB method and added the relevant description of this figure at lines 225-227 in the sub-section 3.3.

Radar Satellite-Based Approaches 

6、The authors have only discussed the advantages of the coarse-resolution optical albedo-based approaches and neglected the possibility of monitoring the high albedo areas of the glaciers with high-resolution SAR satellites and relating it to the glacier annual mass balance. The authors are requested to discuss the contributions of the following articles in this direction and indicate their utility for monitoring cryospheric elements in the absence of optical data. 

-Nagler et al., “Advancement for Snowmelt Monitoring by Means of Sentinel-1 SAR”, Remote Sensing, 2016. 

-Muhuri et al., “Snow cover mapping using polarization fraction variation with temporal RADARSAT-2 C-band full-polarimetric SAR data over the Indian Himalayas”, IEEE JSTARS, 2018. 

-Tsai, Y.L.S., et al., 2019. Remote Sensing of Snow Cover Using Spaceborne SAR: A Review. Remote Sensing.

RE: Thanks for the Reviewer’s suggestion. We have carefully read the three papers above and find that they are about snow cover mapping or snow classification rather than snow albedo estimation. In this study, we need to calculate the altitude-albedo gradient as well as the mass balance-albedo gradient; therefore the glacier surface albedo not the snow cover extent is required in our IAMB method. SAR data can also be used for the equilibrium line altitude (ELA) or transient snow line detection (Winsvold et al., 2018; Garg et al., 2022), and further to estimate annual mass balance with the “ELA method” (Rabatel et al., 2016), but it is beyond the scope of this paper.

Further, glacier surface albedo is generally considered to be the broadband hemispherical averaged reflectance over the shortwave spectrum from 0.35 um to 2.8 um (Brock et al., 2000), thus is usually retrieved from the optical imagery data (e.g. Landsat, MODIS, AVHRR, AVIRIS, SPOT et al.) (Yue et al., 2017). However, the wavelength of synthetic aperture radar (SAR) data is longer than the optical data, which is 15-30 cm, 3.75-7.5 cm, and 2.5-3.75 cm for the L-, C-, and X-band SAR respectively (Bruder, 2013). There is no information on glacier albedo estimation form SAR satellites in literatures according to our best knowledge. So, we have not discussed the availability and contributions of SAR data in this study.

Site Selection

7、The authors are requested to explain the reason for the selection of the Chotta Shigri glacier for this investigation. This is a relatively narrow glacier as compared to a neighbouring glacier, the Bara Shigri, which offers a relatively larger debris-free area and is beneficial for albedo based approach.

RE: Generally, there are three rationales for our choosing the Chotta Shigri glacier in this study, including:

(1) The Chotta Shigri glacier has long and continuous field mass balance observations since 2002 (Azam et al., 2014). These long time series of annual mass balance measurements can facilitate us to test and validate the established IAMB method. We have added the explanation at lines 97-99 in the Section 2.

(2) Although the Bara Shigri glacier is the largest glacier in the Indian state of Himachal Pradesh, the Bara Shigri glacier has no in-situ annual mass balance before 2016 (WGMS, 2022) and has higher  debris-covered regions (about 16%) (Schauwecker et al., 2015) than the Chotta Shigri glacier (about 11%) (Mandal et al., 2020). Therefore, we can not choose the Bara Shigri glacier for the method validation. Actually, considered the bigger areas of glaciated regions, we intend to use the Bara Shigri glacier for method application in the near future.

 (3) In addition, we select the relatively narrow Chotta Shigri glacier for this investigation can also show that the MODImLab albedo with 250-meter resolution performs well over the rugged mountain glaciers.

Table 1

8、The authors present datasets with different solar elevation angles. The reviewer would like to know how the authors have normalized the spectral reflectance from different scenes. For example, in Fig. 5 (b) the area seems to be overexposed and it is difficult to distinguish the glacier boundaries due to the snow cover in the surrounding areas. The authors are requested to consider the use of standard glacier inventories to demarcate the boundaries of the glacier.

RE: (1) This is a clerical mistake in the description of Landsat imagery (sub-section 3.1.2). Considered that the Chotta Shigri glacier is relatively steep and surrounded by high mountains, we have made the topographic correction when calculating glacier surface albedo by the method proposed in Yue et al. (2017). Even so, the influence of low sun elevation angle (<40°) is well known because of the terrain shielding and result in lower albedo values (Traversa et al., 2021). Therefore, the Landsat imagery with lower sun elevation angles (<45°) is excluded to get more accurate glacier albedo in our study. We have added this explanation at the end of sub-section 3.1.2. Please see details at lines 132-136.

(2) Figure 5 shows the original true color Landsat imageries acquired on 29 September 2000, 27 September 2008, 30 September 2009 and 25 September 2013.The sun elevation angles of the four Landsat imageries are similar with each other, which ranges from 49.64° to 52.59°. Different of snow cover extent and snow stage lead to the different color saturation of the four imageries. In this case, the surface albedo is relatively high and homogeneous and did not change significantly (<20%) with elevation (see the dash lines in Figure 5). So, we can not determine the glacier accumulation and ablation areas from these remote sensing images and these albedo datasets are not used for the altitude-albedo gradient estimation. Please see details in the sub-section 4.2 and Figure 6.

(3) The glacier boundaries derived from the Randolph Glacier Inventory (RGI 6.0, released in July 2017), were employed to identify the glaciated regions of the Chhota Shigri glacier. However, we removed the pixels corresponding to debris-covered areas (<4600 m a.s.l.) to avoid the influence on satellite albedo deriving (Brun et al., 2015). Please see details at lines 162-168 in the sub-section 3.1.4. The red solid line in Figure 6 corresponds to debris-free zones in the Chhota Shigri glacier. We have rephrased the figure caption of Figure 6.

Fig. 4

9、It is difficult to understand this figure and the authors have also presented the dates in a cluttered format. The authors are requested to use a smoothly varying colour bar to indicate the temporal change (dates) and plot the changing albedo along this bar.

RE: (1) Maybe our unclear descriptions mislead you. Figure 5 (now in the revised version) illustrates the change of surface albedo with altitude variation over the Chhota Shigri glacier. The glacier albedo and altitude are estimated from the Landsat reflectance and SRTM DEM, respectively. Please see details in sub-section 3.3.

(2) Thanks for the Reviewer’s suggestion. We have also replotted the Figure 5 (in the revised version).The different albedo curves are presented as the acquired date (YYYY-MM-DD) of Landsat imageries. A set of smoothly varying colors is utilized to indicate the different albedo curves. We also rephrased the figure caption of Figure 5.

Reference:

Azam, M.F.; Wagnon, P.; Vincent, C.; Ramanathan, A.L.; Favier, V.; Mandal, A.; Pottakkal, J.G. Processes governing the mass balance of Chhota Shigri Glacier (western Himalaya, India) assessed by point-scale surface energy balance measurements. Cryosphere 2014, 8, 2195-2217.

Brock, B. W., Willis, I. C., & Sharp, M. J. (2000). Measurement and parameterization of albedo variations at Haut Glacier d’Arolla, Switzerland. Journal of Glaciology, 46(155), 675-688.

Bruder, J. A. (2013). IEEE Radar standards and the radar systems panel. IEEE Aerospace and Electronic Systems Magazine, 28(7), 19-22.

Brun, F.; Dumont, M.; Wagnon, P.; Berthier, E.; Azam, M. F.; Shea, J. M.; Sirguey, P.; Rabatel, A.; Ramanathan, A. Seasonal changes in surface albedo of himalayan glaciers from MODIS data and links with the annual mass balance. Cryosphere 2015, 9, 341-355.

Garg V, Thakur P K, Rajak D R, et al. Spatio-temporal changes in radar zones and ELA estimation of glaciers in NyÅlesund using Sentinel-1 SAR[J]. Polar Science, 2022, 31: 100786.

Mandal, A., Ramanathan, A., Azam, M. F., Angchuk, T., Soheb, M., Kumar, N., & Singh, V. B. (2020). Understanding the interrelationships among mass balance, meteorology, discharge and surface velocity on Chhota Shigri Glacier over 2002–2019 using in situ measurements. Journal of Glaciology, 66(259), 727-741.

Rabatel A, Dedieu J P, Vincent C. Spatio-temporal changes in glacier-wide mass balance quantified by optical remote sensing on 30 glaciers in the French Alps for the period 1983–2014[J]. Journal of Glaciology, 2016, 62(236): 1153-1166.

Schauwecker, S., Rohrer, M., Huggel, C., Kulkarni, A., Ramanathan, A. L., Salzmann, N., & Brock, B. (2015). Remotely sensed debris thickness mapping of Bara Shigri glacier, Indian Himalaya. Journal of Glaciology, 61(228), 675-688.

Traversa, G., Fugazza, D., Senese, A., & Frezzotti, M. (2021). Landsat 8 OLI broadband albedo validation in Antarctica and Greenland. Remote Sensing, 13(4), 799.

WGMS (2022): Fluctuations of Glaciers Database. World Glacier Monitoring Service (WGMS), Zurich, Switzerland.

Winsvold S H, Kääb A, Nuth C, et al. Using SAR satellite data time series for regional glacier mapping[J]. The Cryosphere, 2018, 12(3): 867-890.

Yue, X., Zhao, J. U. N., Li, Z., Zhang, M., Fan, J. I. N., Wang, L., & Wang, P. (2017). Spatial and temporal variations of the surface albedo and other factors influencing Urumqi Glacier No. 1 in Tien Shan, China. Journal of Glaciology, 63(241), 899-911.

Author Response File: Author Response.pdf

Reviewer 3 Report

The article titled "Reconstruction of annual glacier mass balance from remote sensing-derived average glacier-wide albedo" by Zhang et al. presents an improved albedo-mass balance (IAMB) method. Please find the specific comments for this manuscript. Authors should incorporate the following remarks for getting published in this journal.

 

The Study is indeed very interesting to read. The authors have tried to present the study in a good way.

 

The language used is easy to comprehend though it has a few mistakes, which I suggest can be done with proofreading by a third person.

 

In the study, the authors present an improved albedo-mass balance (IAMB) method.

I understand the difficulty of obtaining field-validated data in polar regions, but it would be great to have them to test the method.

 

In the conclusion Section, the authors propose that “IAMB method can efficiency quantify the annual glacier-wide mass balance using remote sensing data if the average mass balance can be determined from the geodetic or other method.” However, in my opinion, the advantages and characteristics of the method over the traditional methods are not clear in the paper. I suggest that the authors strengthen the analysis in this point.

 

Meanwhile, it would be better if the method could be verified again at another glacier other than Chhota Shigri.

 

I suggest authors can produce a geological map of Figure 2.

 

 

Author Response

1、The article titled "Reconstruction of annual glacier mass balance from remote sensing-derived average glacier-wide albedo" by Zhang et al. presents an improved albedo-mass balance (IAMB) method. Please find the specific comments for this manuscript. Authors should incorporate the following remarks for getting published in this journal.

The Study is indeed very interesting to read. The authors have tried to present the study in a good way.

The language used is easy to comprehend though it has a few mistakes, which I suggest can be done with proofreading by a third person.

RE: Thanks for the Reviewer’s suggestion. We have carefully read this manuscript and made some revisions to improve it, mainly including: (1) deleting some inconsequential and repeated content in the dataset section; (2) adding a data processing flowchart (Figure 2) to describe the IAMB method in more detail; (3) rewriting the reasons for choosing average glacier albedo in sub-section 5.4; (4) adding the discussions on future prospects and limitations of the IAMB method in sub-section 5.5; (5) changing the image resolution from 300 dpi to 600 dpi and (6) correcting grammatical and spelling mistakes in the full text.

2、In the study, the authors present an improved albedo-mass balance (IAMB) method.

I understand the difficulty of obtaining field-validated data in polar regions, but it would be great to have them to test the method.

RE: Thanks for the Reviewer’s suggestion. Due to lack of intensive in-situ annual mass balance measurements, the improved albedo-mass balance (IAMB) method has only tested and validated in the Chotta Shigri glacier. Next, we intend to select some other glaciers with long-term field annual mass balance observations to verify the availability of this method, especially for the polar glaciers. Please see details at the end of Section 6.

3、In the conclusion Section, the authors propose that “IAMB method can efficiency quantify the annual glacier-wide mass balance using remote sensing data if the average mass balance can be determined from the geodetic or other method.” However, in my opinion, the advantages and characteristics of the method over the traditional methods are not clear in the paper. I suggest that the authors strengthen the analysis in this point.

RE: Thanks for the Reviewer’s suggestion. According to the suggestions from Reviewer #1, we have added sub-section 5.5 to descript the future prospects and limitations of the IAMB method. In the first paragraph of sub-section 5.5, we have analyzed the advantages and characteristics of the IAMB method. Please see details in the sub-section 5.5.

4、 Meanwhile, it would be better if the method could be verified again at another glacier other than Chhota Shigri.

RE: Thanks for the Reviewer’s suggestion. In order to test and verify the availability of the IAMB method, the glacier with long-term and continuous annual mass balance observations is the first to consider. In addition, given that the MODImLab albedo has a relatively low spatial resolution of 250-meters, the area of selected glacier should not be too small. Therefore, the IAMB method has only tested and validated in the Chotta Shigri glacier to date. Test and verification of the IAMB method is still needed on other glaciers. We have added this explanation at the second paragraph in Section 6.

5、I suggest authors can produce a geological map of Figure 2.

RE: We are terribly sorry, but we do not quite follow your gist. Figure 2 (now figure 3 in the revised version) illustrate the spatial distributions of the average summer albedo maps retrieved by MODImLab over Chhota Shigri glacier from 2003 to 2014. The resolution of MODImLab albedo result is 250-meters, so this figure appears a bit of blurry and grainy. We have revised the figure caption to avoid ambiguity, but we do not add the geological map. Please see details in Figure 3.

 

Author Response File: Author Response.pdf

Reviewer 4 Report

The authors have covered the topic of “Reconstruction of annual glacier mass balance from remote sensing-derived average glacier-wide albedo” which is an interesting topic for the researchers/readers. Overall, the work is good and well written but there are some short comes in the manuscript which is needed to be revised before publishing this work. 

 

1.     Carefully check large sentence structures. Very difficult to follow the

2.     Research gap is missing in the introduction part.

3.     Separate section of Study area and Dataset. Dataset is part of the method.

4.     The method and data section need to be concise it’s too big

5.     Maps are not clear provide high-resolution/DPI maps

6.     Results and discussion part need minor revision

For some comments and suggestions please check MS with comments.

 

 

Comments for author File: Comments.pdf

Author Response

Point 1: The authors have covered the topic of “Reconstruction of annual glacier mass balance from remote sensing-derived average glacier-wide albedo” which is an interesting topic for the researchers/readers. Overall, the work is good and well written but there are some shortcomes in the manuscript which is needed to be revised before publishing this work.

RE: Many thanks for the Reviewer’s suggestion. We have carefully read this manuscript and made some revisions to improve it, mainly including: (1) deleting some inconsequential and repeated content in the dataset section; (2) adding a data processing flowchart (now Figure 2 in the revised version) to describe the IAMB method in more detail; (3) rewriting the reasons for choosing average glacier albedo in sub-section 5.4; (4) adding the discussions on future prospects and limitations of the IAMB method in sub-section 5.5; (5) changing the image resolution from 300 dpi to 600 dpi and (6) correcting grammatical and spelling mistakes in the full text.

1. Carefully check large sentence structures. Very difficult to follow the

RE: Thanks for the Reviewer’s suggestion. We have carefully checked these large sentence structures to avoid errors in expression. In the introduction section, we rephrased a sentence as “The well-established glaciological method is a traditional and widely used method for annual mass balance monitoring. However, field observations of annual glacier mass balance remain scarce due to inaccessibility and harsh environmental conditions of the glaciated regions [9].” Please see details at lines 46-50.

2. Research gap is missing in the introduction part.

RE: Thanks for the Reviewer’s suggestion. We have added the research gap in the abstract and introduction sections. Please see details at lines 18-19, and lines 75-78.

3. Separate section of Study area and Dataset. Dataset is part of the method.

RE: Thanks for the Reviewer’s suggestion. We have separated the datasets from study area section, and merged datasets into the method section. Please see details in the Section 2 and Section 3.

4. The method and data section need to be concise it’s too big

RE: Thanks for the Reviewer’s suggestion. We have deleted some inconsequential and repeated content, and done language streamlining in the method and dataset section. Please see details in the  Section 2 and Section 3.

5. Maps are not clear provide high-resolution/DPI maps

RE: Thanks for the Reviewer’s suggestion. We have replotted all the figures (Figure 1 to Figure 9) of the manuscript, changing the image resolution from 300 dpi to 600 dpi.

6. Results and discussion part need minor revision

RE: Thanks for the Reviewer’s suggestion. We have carefully read the results and discussion parts in the manuscript, and made some revision for the content improvement, including: (1) rewriting the reasons for choosing average glacier albedo (the second paragraph of sub-section 5.4); (2) adding the discussions on future prospects and limitations of the IAMB method in sub-section 5.5; and (3) correcting some language errors and narrative ambiguities in the result section.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

This paper has been improved to a certain extent and can be accepted。