Abstract
We compare two independent estimates of the rate of elevation change and geodetic mass balance of the Northern Patagonian Icefield (NPI) between 2000 (3856 km²) and 2012 (3740 km²) from space-borne data. The first is obtained by differencing the Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM) from February 2000 and a Satellite pour l’Observation de la Terre 5 (SPOT5) DEM from March 2012. The second is deduced by fitting pixel-based linear elevation trends over 118 DEMs calculated from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) stereo images acquired between 2000 and 2012. Both methods lead to similar and strongly negative icefield-wide mass balances of -1.02±0.21 and -1.06±0.14 m w.e. yr-1 respectively, which is in agreement with earlier studies. Contrasting glacier responses are observed, with individual glacier mass balances ranging from -0.15 to -2.30 m w.e. yr-1 (standard deviation = 0.49 m w.e. yr-1; N = 38). For individual glaciers, the two methods agree within error bars, except for small glaciers poorly sampled in the SPOT5 DEM due to clouds. Importantly, our study confirms the lack of penetration of the C-band SRTM radar signal into the NPI snow and firn except for a region above 2900 m a.s.l. covering less than 1% of the total area. Ignoring penetration would bias the mass balance by only 0.005 m w.e. yr-1. A strong advantage of the ASTER method is that it relies only on freely available data and can thus be extended to other glacierized areas.
Highlights
Patagonian glaciers and icefields, including the Northern Patagonian Icefield (NPI), are essential indicators of climate change in the southern hemisphere and stand as one of the major contributors to recent sea level rise (Gardner et al, 2013; Mernild and Wilson, 2016)
NPI Mass Balance 2000–2012 mass balance rate estimates are often based on the geodetic method, which allows calculation of glacier volume changes by differentiation of two or more multi-temporal digital elevation models (DEMs) (e.g., Paul et al, 2015; Marzeion et al, 2017)
The first is based on the standard differencing of two DEMs (SRTM and Satellite pour l’Observation de la Terre 5 (SPOT5)) whereas the second method extracts the rate of surface elevation change by fitting a linear trend to over 118 DEMs derived from ASTER stereo images
Summary
Patagonian glaciers and icefields, including the Northern Patagonian Icefield (NPI), are essential indicators of climate change in the southern hemisphere and stand as one of the major contributors to recent sea level rise (Gardner et al, 2013; Mernild and Wilson, 2016). Remote sensing techniques have enabled the spatial coverage of glaciological observations to be extended They are useful in remote and inaccessible areas like the NPI, making it possible to observe and measure glacier variations and to estimate mass balance rate at regional scales (Rignot et al, 2003; Rivera et al, 2007; Lopez et al, 2010; Davies and Glasser, 2012; Willis et al, 2012a,b; Dixon and Ambinakudige, 2015; Jaber et al, 2016). In particular for the NPI, Willis et al (2012a) measured mass balance using the Shuttle Radar Topography Mission (SRTM) DEM and a collection of freely available Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) DEMs from 2001 to 2011. Jaber et al (2016) provided a mass balance estimate for 2000–2014 by comparing two interferometric DEMs, SRTM, and TanDEM-X
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