Spatial distribution of surface albedo at the Forni Glacier (Stelvio National Park, Central Italian Alps)

Fugazza, Davide; Senese, Antonella; Azzoni, Roberto Sergio; Maugeri, Maurizio; Diolaiuti, Guglielmina

doi:10.1016/j.coldregions.2016.02.006

Cited by 30 publications

(33 citation statements)

References 33 publications

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“…In agreement with previous satellite investigations on Alpine glaciers, low α VIS values are estimated in the Morteratsch ablation zone (Brun et al, 2015;Dumont et al, 2011;Fugazza et al, 2016;Klok et al, 2004;Naegeli et al, 2015Naegeli et al, , 2017. This decrease in albedo can be explained by both an increase in LAI content and/or variations of the snow and ice grain properties.…”

Section: Discussionsupporting

confidence: 75%

Impact of impurities and cryoconite on the optical properties of the Morteratsch Glacier (Swiss Alps)

et al. 2017

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Abstract. The amount of reflected energy by snow and ice plays a fundamental role in their melting processes. Different non-ice materials (carbonaceous particles, mineral dust (MD), microorganisms, algae, etc.) can decrease the reflectance of snow and ice promoting the melt. The object of this paper is to assess the capability of field and satellite (EO-1 Hyperion) hyperspectral data to characterize the impact of light-absorbing impurities (LAIs) on the surface reflectance of ice and snow of the Vadret da Morteratsch, a large valley glacier in the Swiss Alps. The spatial distribution of both narrow-band and broad-band indices derived from Hyperion was analyzed in relation to ice and snow impurities. In situ and laboratory reflectance spectra were acquired to characterize the optical properties of ice and cryoconite samples. The concentrations of elemental carbon (EC), organic carbon (OC) and levoglucosan were also determined to characterize the impurities found in cryoconite. Multi-wavelength absorbance spectra were measured to compare the optical properties of cryoconite samples and local moraine sediments. In situ reflectance spectra showed that the presence of impurities reduced ice reflectance in visible wavelengths by 80-90 %. Satellite data also showed the outcropping of dust during the melting season in the upper parts of the glacier, revealing that seasonal input of atmospheric dust can decrease the reflectance also in the accumulation zone of the glacier. The presence of EC and OC in cryoconite samples suggests a relevant role of carbonaceous and organic material in the darkening of the ablation zone. This darkening effect is added to that caused by fine debris from lateral moraines, which is assumed to represent a large fraction of cryoconite. Possible input of anthropogenic activity cannot be excluded and further research is needed to assess the role of human activities in the darkening process of glaciers observed in recent years.

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Section: Discussionsupporting

confidence: 75%

Impact of impurities and cryoconite on the optical properties of the Morteratsch Glacier (Swiss Alps)

et al. 2017

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“…Once the extension of the surface covered by fine debris is quantified, the relation between d and α could be applied, thus deriving an albedo map. The latter will feature a higher resolution (pixel size of a few centimeters) than the ones derived from other approaches such as Landsat images (pixel size of 15 m × 15 m, Fugazza et al, 2016).…”

Section: Discussionmentioning

confidence: 99%

Estimating ice albedo from fine debris cover quantified by a semi-automatic method: the case study of Forni Glacier, Italian Alps

et al. 2016

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Abstract. In spite of the quite abundant literature focusing on fine debris deposition over glacier accumulation areas, less attention has been paid to the glacier melting surface. Accordingly, we proposed a novel method based on semiautomatic image analysis to estimate ice albedo from fine debris coverage (d). Our procedure was tested on the surface of a wide Alpine valley glacier (the Forni Glacier, Italy), in summer 2011, 2012 and 2013, acquiring parallel data sets of in situ measurements of ice albedo and high-resolution surface images. Analysis of 51 images yielded d values ranging from 0.01 to 0.63 and albedo was found to vary from 0.06 to 0.32. The estimated d values are in a linear relation with the natural logarithm of measured ice albedo (R = −0.84). The robustness of our approach in evaluating d was analyzed through five sensitivity tests, and we found that it is largely replicable. On the Forni Glacier, we also quantified a mean debris coverage rate (C r ) equal to 6 g m −2 per day during the ablation season of 2013, thus supporting previous studies that describe ongoing darkening phenomena at Alpine debris-free glaciers surface. In addition to debris coverage, we also considered the impact of water (both from melt and rainfall) as a factor that tunes albedo: meltwater occurs during the central hours of the day, decreasing the albedo due to its lower reflectivity; instead, rainfall causes a subsequent mean daily albedo increase slightly higher than 20 %, although it is short-lasting (from 1 to 4 days).

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“…Several narrow-to-broadband formulae to retrieve albedo are mentioned in the literature [28], but solely the method by Knap et al [29] is frequently used in glaciological studies (e.g., [20][21][22]). An alternative approach by Liang [30] was never validated for snow and ice surfaces.…”

Section: Introductionmentioning

confidence: 99%

“…Several studies have used Landsat or MODIS data to derive glacier surface albedo distribution [20][21][22] and compared their results with local automated weather stations [23] or linked them to glacier mass balance estimates [2,24]. In particular, the 500 m MODIS albedo product was used in several studies [2][3][4]25].…”

Section: Introductionmentioning

confidence: 99%

Cross-Comparison of Albedo Products for Glacier Surfaces Derived from Airborne and Satellite (Sentinel-2 and Landsat 8) Optical Data

et al. 2017

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Surface albedo partitions the amount of energy received by glacier surfaces from shortwave fluxes and modulates the energy available for melt processes. The ice-albedo feedback, influenced by the contamination of bare-ice surfaces with light-absorbing impurities, plays a major role in the melting of mountain glaciers in a warming climate. However, little is known about the spatial and temporal distribution and variability of bare-ice glacier surface albedo under changing conditions. In this study, we focus on two mountain glaciers located in the western Swiss Alps and perform a cross-comparison of different albedo products. We take advantage of high spectral and spatial resolution (284 bands, 2 m) imaging spectrometer data from the Airborne Prism Experiment (APEX) and investigate the applicability and potential of Sentinel-2 and Landsat 8 data to derive broadband albedo products. The performance of shortwave broadband albedo retrievals is tested and we assess the reliability of published narrow-to-broadband conversion algorithms. The resulting albedo products from the three sensors and different algorithms are further cross-compared. Moreover, the impact of the anisotropy correction is analysed depending on different surface types. While degradation of the spectral resolution impacted glacier-wide mean albedo by about 5%, reducing the spatial resolution resulted in changes of less than 1%. However, in any case, coarser spatial resolution was no longer able to represent small-scale variability of albedo on glacier surfaces. We discuss the implications when using Sentinel-2 and Landsat 8 to map dynamic glaciological processes and to monitor glacier surface albedo on larger spatial and more frequent temporal scales.

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Spatial distribution of surface albedo at the Forni Glacier (Stelvio National Park, Central Italian Alps)

Cited by 30 publications

References 33 publications

Impact of impurities and cryoconite on the optical properties of the Morteratsch Glacier (Swiss Alps)

Impact of impurities and cryoconite on the optical properties of the Morteratsch Glacier (Swiss Alps)

Estimating ice albedo from fine debris cover quantified by a semi-automatic method: the case study of Forni Glacier, Italian Alps

Cross-Comparison of Albedo Products for Glacier Surfaces Derived from Airborne and Satellite (Sentinel-2 and Landsat 8) Optical Data

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