Abstract
Abstract. We introduce an algorithm (Watta) which automatically calculates supraglacial lake bathymetry and detects potential ice layers along tracks of the ICESat-2 (Ice, Cloud, and Land Elevation Satellite) laser altimeter. Watta uses photon heights estimated by the ICESat-2 ATL03 product and extracts supraglacial lake surface, bottom, and depth corrected for refraction 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 8 Operational Land Imager (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 (available for 45 of these lakes) 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 (Continuous Airborne Mapping By Optical Translator) 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.
Highlights
Ice loss from Greenland and Antarctica is the greatest current contributor to rising sea levels, and paleodata and modeling efforts indicate that enhanced mass loss of these ice sheets may become irreversible if certain major tipping points are passed (IPCC, 2019)
Our results suggest that the use of multiple imagery sources, in combination with altimetry-based depths, can move towards capturing the evolution of supraglacial hydrology at improved spatial and temporal scales
In Antarctica, this was largely driven by increased ocean melting of outlet glaciers (Rignot et al, 2019), while on the Greenland Ice Sheet mass loss is further promoted by increased surface melt and runoff (Mouginot et al, 2019)
Summary
Ice loss from Greenland and Antarctica is the greatest current contributor to rising sea levels, and paleodata and modeling efforts indicate that enhanced mass loss of these ice sheets may become irreversible if certain major tipping points are passed (IPCC, 2019). Concurrent with the increase in melt extent and duration, supraglacial lakes – which form when meltwater runoff collects in local topographic lows – are a common feature on large parts of the ice sheets and have become more extensive and have advanced inland toward higher elevations in the past decades (Gledhill and Williamson, 2018; Leeson et al, 2015; Howat et al, 2013). The ICESat-2 (Ice, Cloud, and Land Elevation Satellite) laser altimeter data, available since 2018, has introduced the potential to replace the in situ measurements used in empirical (supraglacial lake depth) bathymetric methods with satellite laser bathymetric depths at a high vertical resolution, extracting lake volumes from imagery (Parrish et al, 2019; Albright and Glennie, 2020; Thomas et al, 2021). We present initial results exploiting this dataset, as well as introducing the Watta ICESat-2 surface feature detection algorithm
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