the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
29 Jan 2021
29 Jan 2021
Supraglacial lake bathymetry automatically derived from ICESat-2 constraining lake depth estimates from multi-source satellite imagery
- 1Earth Systems Science Interdisciplinary Center, University of Maryland, College Park, MD
- 2NASA Goddard Space Flight Center, Greenbelt, MD
- 3Department of Atmospheric and Oceanic Sciences, University of Colorado Boulder, Boulder, CO, USA
- 4Department of Physics, Institute for Marine and Atmospheric Research, Utrecht University, Utrecht, NL
- 5Faculty of Civil Engineering and Geosciences, Delft University of Technology, Delft, NL
- 1Earth Systems Science Interdisciplinary Center, University of Maryland, College Park, MD
- 2NASA Goddard Space Flight Center, Greenbelt, MD
- 3Department of Atmospheric and Oceanic Sciences, University of Colorado Boulder, Boulder, CO, USA
- 4Department of Physics, Institute for Marine and Atmospheric Research, Utrecht University, Utrecht, NL
- 5Faculty of Civil Engineering and Geosciences, Delft University of Technology, Delft, NL
Abstract. We introduce an algorithm (Watta), which automatically calculates supraglacial lake bathymmetry and potential ice layers along tracks of the ICESat-2 laser altimeter. Watta uses photon heights estimated by the ICESat-2 ATL03 product and extracts supraglacial lake surface, bottom, corrected depth and (sub)surface ice cover in addition to producing surface heights at the native resolution of the ATL03 photon cloud. These measurements are used to constrain empirical estimates of lake depth from satellite imagery, which were thus far dependent on sparse sets of in-situ measurements for calibration. Imagery sources include Landsat OLI, Sentinel-2 and high-resolution Planet Labs PlanetScope and SkySat data, used here for the first time to calculate supraglacial lake depths. The Watta algorithm was developed and tested using a set of 46 lakes near Sermeq Kujalleq (Jakobshavn) glacier in Western Greenland, and we use multiple imagery sources to assess the use of the red vs green band to extrapolate depths along a profile to full lake volumes. We use Watta-derived estimates in conjunction with high-resolution imagery from both satellite-based sources (tasked over the season) and nearly-simultaneous Operation IceBridge CAMBOT imagery (on a single airborne flight) for a focused study of the drainage of a single lake over the 2019 melt season. Our results suggest that the use of multiple imagery sources (both publicly-available and commercial) in combination with altimetry-based depths, can move towards capturing the evolution of supraglacial hydrology at improved spatial and temporal scales.
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Rajashree Tri Datta and Bert Wouters
Status: open (until 26 Mar 2021)
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RC1: 'Reviewer response to tc-2021-4', Jennifer Arthur, 22 Feb 2021
reply
General comments:
This manuscript presents a new algorithm, ‘Watta’, for automatically extracting supraglacial lake depth estimates using ICESat-2 geolocated photon heights (ATL03) which are then used to validate empirically-derived lake depths from Landsat 8, Sentinel-2, Planet Labs Skysat and PlanetScope imagery. The authors test the algorithm performance on 46 supraglacial lakes near Jakobshavn Glacier in West Greenland during an intense melt season (2019). Finally, they use this stacked dataset in combination with Operation IceBridge imagery to track volume, drainage mechanisms and ice cover evolution of two individual lakes in this region.
Supraglacial lakes form in the ablation zones of Greenland and Antarctica during the summer melt season and can impact ice sheet dynamics, making lake detection and depth retrieval important. However, lake volumes have been difficult to quantify due to a lack of in-situ measurements and uncertainties associated with image-based methods. This manuscript builds upon other recent studies by applying a novel method for lake depth extraction, which is the first application of high-resolution Planet Labs satellite imagery to calculate supraglacial lake depths in combination with other imagery sources and ICESat-2 heights. It also provides useful insight into lake dynamics and ice cover evolution, which to date have been limited by the comparatively coarse resolution of publicly-available satellite datasets (Sentinel, Landsat).
Therefore, it is my view that the findings are of broad interest to the cryospheric community and represent a promising step forward for studying supraglacial hydrology and dynamics. I look forward to seeing further development of this method and its applications elsewhere on the Greenland and Antarctic ice sheets, particularly on floating ice shelves.
In general, this is a well-written manuscript and most of my comments are relatively minor. I would like to see in places some additional detail around the discussion of lake depth retrieval methods (see specific comments attached).
Lastly, The Cryosphere’s data policy states that “Authors are required to provide a statement on how their underlying research data can be accessed. This must be placed as the section "Data availability" at the end of the manuscript.” Although the authors state at the end of the manuscript that the Matlab code will be converted and shared publicly, I would like to see this section added including statements of how Landsat, Sentinel and Planet imagery can be accessed.
Once the authors address these points and my comments below, I can therefore recommend that this manuscript is suitable for publication in The Cryosphere.
Rajashree Tri Datta and Bert Wouters
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Supraglacial lake depths from ICESat-2 and multiple imagery sources over Western Greenland Rajashree Tri Datta and Bert Wouters https://doi.org/10.5281/zenodo.4067629
Rajashree Tri Datta and Bert Wouters
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