High-resolution debris-cover mapping using UAV-derived thermal imagery: limits and opportunities
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Published:2023-03-10
Issue:3
Volume:17
Page:1165-1184
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ISSN:1994-0424
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Container-title:The Cryosphere
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language:en
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Short-container-title:The Cryosphere
Author:
Gök Deniz Tobias, Scherler DirkORCID, Anderson Leif StefanORCID
Abstract
Abstract. Debris-covered glaciers are widespread in high mountain
ranges on earth. However, the dynamic evolution of debris-covered glacier
surfaces is not well understood, in part due to difficulties in mapping
debris-cover thickness in high spatiotemporal resolution. In this study, we
present land surface temperatures (LSTs) of supraglacial debris cover and their
diurnal variability measured from an unpiloted aerial vehicle (UAV) at a
high (15 cm) spatial resolution. We test two common approaches to derive
debris-thickness maps by (1) solving a surface energy balance model (SEBM)
in conjunction with meteorological reanalysis data and (2) least squares
regression of a rational curve using debris-thickness field measurements. In
addition, we take advantage of the measured diurnal temperature cycle and
estimate the rate of change of heat storage within the debris cover. Both
approaches resulted in debris-thickness estimates with an RMSE of 6 to 8 cm
between observed and modeled debris thicknesses, depending on the time of
the day. Although the rational curve approach requires in situ field
measurements, the approach is less sensitive to uncertainties in LST
measurements compared to the SEBM approach. However, the requirement of
debris-thickness measurements can be an inhibiting factor that supports the
SEB approach. Because LST varies throughout the day, the success of a
rational function to express the relationship between LST and debris
thickness also varies predictably with the time of day.
During the period when the debris cover is warming, LST is heavily influenced by the aspect of the terrain. As a result, clear-sky morning flights that do not consider the aspect effects can be problematic.
Our sensitivity analysis of various
parameters in the SEBM highlights the relevance of the effective thermal
conductivity when LST is high. The residual and variable bias of UAV-derived
LSTs during a flight requires calibration, which we achieve with bare-ice
surfaces. The model performance would benefit from more accurate LST
measurements, which are challenging to achieve with uncooled sensors in high mountain landscapes.
Funder
H2020 European Research Council
Publisher
Copernicus GmbH
Subject
Earth-Surface Processes,Water Science and Technology
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