the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 06 Dec 2024
Glacier surge monitoring from temporally dense elevation time series: application to an ASTER dataset over the Karakoram region
Abstract. Glacier surges are spectacular events that lead to surface elevation changes of tens of meter in a period of a few months to a few years, with different patterns of mass transport. Existing methods of elevation change estimate of surges, and subsequent quantification of their mass transported, rely on differencing pairs of digital elevation models (DEMs) that may not be acquired regularly in time. In this study, we propose a workflow to filter and interpolate a dense time series of DEMs specifically for the study of surge events. We test this workflow on a global 20-year dataset of DEMs from the optical satellite sensor Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). The multi-step procedure includes linear non-parametric Locally Weighted Regression and Smoothing Scatterplots (LOWESS) filtering and Approximation by Localized Penalized Splines (ALPS) interpolation. We run the workflow over the Karakoram mountain range (High Mountain Asia). We compare the produced dataset to previous studies for four selected surge events (surges of Hispar, Khurdopin, Kyagar and Yazghil glaciers). We demonstrate that our workflow captures thickness changes at monthly scale with detailed patterns of mass transportation. Such patterns includes surge front propagation, changes in dynamic balance line, and slow surge onset among others, and allows an unprecedentedly detailed description of glacier surges at the scale of a large region. The workflow preserves most of the elevation change signal, with underestimation or smoothing in a limited number of surge cases.
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RC1: 'Comment on egusphere-2024-3480', William Kochtitzky, 19 Dec 2024
The authors present a new method of computing elevation changes during surge events when numerous elevation measurements are available for glaciers in a relatively short time period (annual to decadal). The method is novel and advances our knowledge of surging. They provide new insight into several different surge events that have been previously documented. I recommend the paper be published, but I have a few minor comments that could strengthen the paper below. My main criticism is that the authors seem to lack a quantified uncertainty of their results. For example, it would be greatly beneficial to add uncertainty to table 1. I don't think another round of review is necessary, I am happy to see it published after the authors make these minor changes.
-Will Kochtitzky
Line 19 – change “in” to “is” and “cluster” to “clusters”
Line 75 – “2020 to 2020” – presumably you mean 2000 to 2020?
Line 77 – “terms” not “term”
Figure 2 – very cool figure, but I am having a hard time understanding it. I think part of the problem is that I don’t get the colorbar showing the density of DEMs. I don’t see this mentioned in the caption. Is it showing how much of each DEM is good data? Maybe don’t make the line and the colorbar blue to add clarity – the caption is confusing which blue you are referring to.
Page 5 – can you give us a sense of the data that you filtered out? What is the percent of the data that was filtered out of your study?
Line 125 – “too sensitive” not “to sensitive”
Figure 6 caption – second sentence should be “all show” not “show all”
Figure 7 caption – you say in the text what the red circles are, but this should also be added to the caption for clarity
Figure 8 – “distance from glacier source” is confusing terminology, presumably you are referring to the accumulation area, but it is an area, it is not a point that you can start from. Could you all this the “distance from glacier head”? (also line 254)
Line 245-250 – this is very interesting – do you think you are not capturing the mass fully? Where could it be coming from? Are parts of the reservoir zone not included in your calculations?
Line 268 – “extend” not “extends” – “from this area” not “of this area”
Table 1 – what are your uncertainties on these measurements? This is critical since any imbalance outside the uncertainty would be a more important signal. Can you get these like you did for figure 6?
Figure 10 – shouldn’t the colorbar be elevation difference? Change implies the difference is real, but if I understand this correctly, the difference should be 0.
Line 323 – should read “here at a similar time” – add a
Line 323 – should read “The fact that the reservoir area does not extend above the icefall has already been observed…”
Line 327 – “timescales” not “timescale”
Line 330 – are they within uncertainties?
Line 333 – “appear” not “appears”
Line 334 – “has” not “have”
Line 337 – “has” not “have”
Line 338 – the main sentence on this line is grammatically incorrect, I am not sure what you are trying to say
Line 339 – “on” makes this sentence grammatically incorrect
Line 341 – “There are several”
Line 413 – “exceed” not “exceeds”
Figure 12 – need to add what areas A, B, and C mean to the caption
Line 429 – remove one of the “a”
Line 431 – “does less alter neighboring pixels” – grammatical error
Citation: https://doi.org/10.5194/egusphere-2024-3480-RC1 -
RC2: 'Comment on egusphere-2024-3480', Mingyang Lv, 13 Jan 2025
This study provides a new quantifying approach to describe the elevation change patterns of glacier surge events, based on high temporal resolution successive DEMs. The method applied to automatically detect the surge elevation signals is inspiring, and its application on large scales would be quite interesting. I recommend the paper be published after the following suggestions are considered by the authors.
- About the selected time series
To better illustrate the elevation change patterns over the reservoir and receiving areas during surge events, I suggest the authors to add more number of typical time series analysis results in the paper body or Appendix.
- About the method
Start date and end date of glacier surge events are one of key information to describe the surge process. It will be more convincing if the authors add more information about the criterion to identify the start and end dates of these glacier surge events, based on the processed DEM time series datasets.
- About the temporal information of the glacier surge events
In the Section 4.3, the authors used multiple temporal expression formats simultaneously, such as “mid-2014” in Line 234 and “late 2015” in Line 264. According to Fig. 8 and Tab. 1, the start and end dates of surge events are described in monthly units. In order to show the method could realize monthly glacier surge monitoring, the temporal expression formats could better be unified as monthly units.
Specific comments
Figure 2 – in this figure, the orange part is easy to understand, but the blue part is not. The legend of this figure could be improved.
Line 65 – change “surges” to “surge”
Line 228 – change “five kilometres” to “5 kilometres”.
Line 254 – it seems like “glacier source” is not a common glaciology terminology, perhaps what you are referring to is “the highest peak of the glacier centerline” or “the top end (head) of the glacier”. Please check it. (also Figure 8)
Line 257 - “actual surge” is not a fixed term, please check. Maybe It can be replaced by “surge active phase”.
Line 262 - change “ten kilometres” to “10 kilometres”.
Line 271 - change “a full cycle” to “a full surge cycle”.
Table 1 - you may also add the areas of reservoir and receiving polygons for each glacier.
Table 2 - the Product ID and Acquisition Time of reference DEMs may be added to Appendix.
Figure 10 - the labels of points TSa-c should be indicated in both Fig. 6 and Fig. 10.
Citation: https://doi.org/10.5194/egusphere-2024-3480-RC2 - RC3: 'Comment on egusphere-2024-3480', Gregoire Guillet, 17 Jan 2025
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