Correction of broadband snow albedo measurements affected by unknown slope and sensor tilts

Abstract. Geometric effects induced by the underlying terrain slope or by tilt errors of the radiation sensors lead to an erroneous measurement of snow or ice albedo. Consequently, artificial diurnal albedo variations in the order of 1–20 % are observed. The present paper proposes a general method to correct tilt errors of albedo measurements in cases where tilts of both the sensors and the slopes are not accurately measured or known. We demonstrate that atmospheric parameters for this correction model can either be taken from a nearby well-maintained and horizontally levelled measurement of global radiation or alternatively from a solar radiation model. In a next step the model is fitted to the measured data to determine tilts and directions of sensors and the underlying terrain slope. This then allows us to correct the measured albedo, the radiative balance and the energy balance. Depending on the direction of the slope and the sensors a comparison between measured and corrected albedo values reveals obvious over- or underestimations of albedo. It is also demonstrated that differences between measured and corrected albedo are generally highest for large solar zenith angles.</jats:p

Seismic characterization of a rapidly-rising jökulhlaup cycle at the A.P. Olsen Ice Cap, NE-Greenland

Rapidly-rising jökulhlaups, or glacial outburst floods, are a phenomenon with a high potential for damage. The initiation and propagation processes of a rapidly-rising jökulhlaup are still not fully understood. Seismic monitoring can contribute to an improved process understanding, but comprehensive long-term seismic monitoring campaigns capturing the dynamics of a rapidly-rising jökulhlaup have not been reported so far. To fill this gap, we installed a seismic network at the marginal, ice-dammed lake of the A.P. Olsen Ice Cap (APO) in NE-Greenland. Episodic outbursts from the lake cause flood waves in the Zackenberg river, characterized by a rapid discharge increase within a few hours. Our 6 months long seismic dataset comprises the whole fill-and-drain cycle of the ice-dammed lake in 2012 and includes one of the most destructive floods recorded so far for the Zackenberg river. Seismic event detection and localization reveals abundant surface crevassing and correlates with changes of the river discharge. Seismic interferometry suggests the existence of a thin basal sedimentary layer. We show that the ballistic part of the first surface waves can potentially be used to infer medium changes in both the ice body and the basal layer. Interpretation of time-lapse interferograms is challenged by a varying ambient noise source distribution.ISSN:0022-1430ISSN:1727-565

Point measurements of winter mass balance of Freya Glacier, Greenland, in 2011/2012

On 2017-10-13 it was noted, that the snow density values given here (e.g. 0.38) corresponded to the unit g/cm**3. The values were recalculated (*1000) to fit the unit kg/m**3

Mass balance of Freya Glacier, Greenland, in 2008/2009

Mass balance of Freya Glacier, Greenland, in 2008/200

Point measurements of annual mass balance of Freya Glacier, Greenland, in 2013/2014

Point measurements of annual mass balance of Freya Glacier, Greenland, in 2013/201

Mass balance of Freya Glacier, Greenland, in 2007/2008

Mass balance of Freya Glacier, Greenland, in 2007/200

Mass balance of Freya Glacier, Greenland, in 2010/2011

Mass balance of Freya Glacier, Greenland, in 2010/201