In situ continuous visible and near-infrared spectroscopy of an alpine snowpack

Dumont, Marie; Arnaud, Laurent; Picard, Ghislain; Libois, Quentin; Lejeune, Yves; Nabat, Pierre; Voisin, Didier; Morin, Samuel

doi:10.5194/tc-11-1091-2017

Cited by 62 publications

(114 citation statements)

References 58 publications

(103 reference statements)

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“…Higher resolution imagery might help resolve small scale variability around the station that is not resolved in Landsat 30-m data but that is known from the experience of the field visits. The AWS albedo measurements may also be affected by measurement biases due to the natural instability of the substratum on which the AWSs are placed, e.g., tilted surface slope below the downward pyranometer [36] or inaccurate horizontal leveling of the sensor.…”

Section: Discussionmentioning

confidence: 99%

Evaluation of MODIS Albedo Product over Ice Caps in Iceland and Impact of Volcanic Eruptions on Their Albedo

et al. 2017

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Albedo is a key variable in the response of glaciers to climate. In Iceland, large albedo variations of the ice caps may be caused by the deposition of volcanic ash (tephra). Sparse in situ measurements are insufficient to characterize the spatial variation of albedo over the ice caps due to their large size. Here we evaluated the latest MCD43 MODIS albedo product (collection 6) to monitor albedo changes over the Icelandic ice caps using albedo measurements from ten automatic weather stations on Vatnajökull and Langjökull. Furthermore, we examined the influence of the albedo variability within MODIS pixels by comparing the results with a collection of Landsat scenes. The results indicate a good ability of the MODIS product to characterize the seasonal and interannual albedo changes with correlation coefficients ranging from 0.47 to 0.90 (median 0.84) and small biases ranging from −0.07 to 0.09. The root-mean square errors (RMSE) ranging from 0.08 to 0.21, are larger than that from previous studies, but we did not discard the retrievals flagged as bad quality to maximize the amount of observations given the frequent cloud obstruction in Iceland. We found a positive but non-significant relationship between the RMSE and the subpixel variability as indicated by the standard deviation of the Landsat albedo within a MODIS pixel (R = 0.48). The summer albedo maps and time series computed from the MODIS product show that the albedo decreased significantly after the 2010 Eyjafjallajökull and 2011 Grímsvötn eruptions on all the main ice caps except the northernmost Drangajökull. A strong reduction of the summer albedo by up to 0.6 is observed over large regions of the accumulation areas. These data can be assimilated in an energy and mass balance model to better understand the relative influence of the volcanic and climate forcing to the ongoing mass losses of Icelandic ice caps.

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Section: Discussionmentioning

confidence: 99%

Evaluation of MODIS Albedo Product over Ice Caps in Iceland and Impact of Volcanic Eruptions on Their Albedo

et al. 2017

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“…In addition to the instrumental errors, the surface slope at the footprint scale may influence the retrieval results. Using data from Picard et al (2016), Dumont et al (2017) found variations of the surface slope caused by wind drift at Dome C of ±2 • . They estimated a resulting uncertainty of 10 % in retrieved SSA due to these variations of the surface slope.…”

Section: Retrieval Of Optical Snow Grain Size From Spectral Albedo Mementioning

confidence: 99%

“…Measured quantity Specifications tral Modular Airborne Radiation measurement sysTem (SMART), which applies an active horizontal stabilization of the optical inlets to correct for aircraft movement (Wendisch et al, 2001;Ehrlich et al, 2008). SMART albedo measurements have an estimated uncertainty between 4.1 and 8.1 %, also taking into consideration uncertainties due to the active horizontal stabilization of 1.0 %.…”

Section: Instrumentmentioning

confidence: 99%

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Comparison of different methods to retrieve optical-equivalent snow grain size in central Antarctica

et al. 2017

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Abstract. The optical-equivalent snow grain size affects the reflectivity of snow surfaces and, thus, the local surface energy budget in particular in polar regions. Therefore, the specific surface area (SSA), from which the optical snow grain size is derived, was observed for a 2-month period in central Antarctica (Kohnen research station) during austral summer 2013/14. The data were retrieved on the basis of ground-based spectral surface albedo measurements collected by the COmpact RAdiation measurement System (CORAS) and airborne observations with the Spectral Modular Airborne Radiation measurement sysTem (SMART). The snow grain size and pollution amount (SGSP) algorithm, originally developed to analyze spaceborne reflectance measurements by the MODerate Resolution Imaging Spectroradiometer (MODIS), was modified in order to reduce the impact of the solar zenith angle on the retrieval results and to cover measurements in overcast conditions. Spectral ratios of surface albedo at 1280 and 1100 nm wavelength were used to reduce the retrieval uncertainty. The retrieval was applied to the ground-based and airborne observations and validated against optical in situ observations of SSA utilizing an IceCube device. The SSA retrieved from CORAS observations varied between 27 and 89 m 2 kg −1 . Snowfall events caused distinct relative maxima of the SSA which were followed by a gradual decrease in SSA due to snow metamorphism and wind-induced transport of freshly fallen ice crystals. The ability of the modified algorithm to include measurements in overcast conditions improved the data coverage, in particular at times when precipitation events occurred and the SSA changed quickly. SSA retrieved from measurements with CORAS and MODIS agree with the in situ observations within the ranges given by the measurement uncertainties. However, SSA retrieved from the airborne SMART data slightly underestimated the ground-based results.

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“…The AWS albedo measurements may also be affected by measurements biases due to the natural instability of the substratum on which are placed the AWSs, e.g. tilted surface slope below the downward pyranometer [35] or inaccurate horizontal leveling of the sensor.…”

Section: Discussionmentioning

confidence: 99%

Evaluation of MODIS Albedo Product over Ice Caps in Iceland and Impact of Volcanic Eruptions on Their Albedo

Gascoin¹,

Guðmundsson²,

Ađalgeirsdóttir³

et al. 2017

Preprint

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Abstract:Albedo is a key variable in the response of glaciers to climate. In Iceland, large albedo variations in the ice caps may be caused by the deposition of volcanic ash (tephra). Sparse in situ field measurements are insufficient to characterize the spatial variation of albedo over the ice caps. Here we evaluate the latest MCD43 MODIS albedo product (collection 6) to monitor albedo over the Icelandic ice caps using albedo from ten automatic weather stations in Vatnajökull and Langjökull as ground truth. We examine the influence of the albedo variability within MODIS pixels by comparing the results with a collection of Landsat scenes. The results indicate a good ability of the MODIS product to characterize the seasonal and interannual albedo changes with correlation coefficients ranging from 0.47 to 0.90 (median 0.84) and a small bias ranging from -0.07 to 0.09. The root-mean square errors (RMSE) ranging from 0.08 and 0.21, is larger than that from previous studies, but we did not discard the retrievals flagged as bad quality to maximize the amount of observations given the frequent cloud obstruction in Iceland. We find a positive but non-significant relationship between the RMSE and the subpixel variability as indicated by the standard deviation of the Landsat albedo within the MODIS pixel (R=0.48). The summer albedo maps and time series computed from the MODIS product show that the albedo decreased significantly after the Eyjafjallajökull and Grímsvötn eruptions in 2010 and 2011 in all the main ice caps (except the northernmost Drangajökull), with albedo reduction up to 0.6 over large regions of the accumulation areas. Following this validation, these data will be assimilated in an energy and mass balance model of to better understand the relative influence of the volcanic and climate forcing to the ongoing mass losses of Icelandic ice caps.

show abstract

In situ continuous visible and near-infrared spectroscopy of an alpine snowpack

Cited by 62 publications

References 58 publications

Evaluation of MODIS Albedo Product over Ice Caps in Iceland and Impact of Volcanic Eruptions on Their Albedo

Evaluation of MODIS Albedo Product over Ice Caps in Iceland and Impact of Volcanic Eruptions on Their Albedo

Comparison of different methods to retrieve optical-equivalent snow grain size in central Antarctica

Evaluation of MODIS Albedo Product over Ice Caps in Iceland and Impact of Volcanic Eruptions on Their Albedo

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