Abstract
Abstract. Understanding the evolution of melt ponds on Arctic sea ice is important for climate model parameterisations, weather forecast models and process studies involving mass, energy and biogeochemical exchanges across the ocean–sea ice–atmosphere interface. A field campaign was conducted in a region of level first-year sea ice (FYI) in the central Canadian Arctic Archipelago (CAA), during the summer of 2012, to examine the potential for estimating melt pond fraction (fp) from satellite synthetic aperture radar (SAR). In this study, 5.5 GHz (C-band) dual co- (HH + VV – horizontal transmit and horizontal receive + vertical transmit and vertical receive) and cross-polarisation (HV + HH – horizontal transmit and vertical receive + horizontal transmit and horizontal receive) radar scatterometer measurements of melt-pond-covered FYI are combined with ice and pond properties to analyse the effects of in situ physical and morphological changes on backscatter parameters. Surface roughness statistics of ice and ponds are characterised and compared to the validity domains of the Bragg and integral equation model (IEM) scattering models. Experimental and model results are used to outline the potential and limitations of the co-polarisation ratio (VV / HH) for retrieving melt pond information, including fp, at large incidence angles (≥35°). Despite high variability in cross-polarisation ratio (HV / HH) magnitudes, increases at small incidence angles (<30°) are attributed to the formation of ice lids on ponds. Implications of the results for pond information retrievals from satellite C-, L- and P-band SARs are discussed.
Highlights
A recent shift from predominantly thicker, older multi-year sea ice (MYI) to thinner, smoother first-year sea ice (FYI) has occurred in response to atmospheric and oceanic warming in the Arctic (Perovich et al, 2007; Kwok et al, 2009)
This paper presents in situ surface roughness and C-band scatterometer measurements made on level, landfast FYI in the Canadian Arctic Archipelago (CAA) during advanced melt
We have presented results from the in situ component of a study conducted in the CAA during June 2012, aimed at understanding the multi-scale, polarimetric, C-band backscatter behaviour of level FYI ice during ponding
Summary
A recent shift from predominantly thicker, older multi-year sea ice (MYI) to thinner, smoother first-year sea ice (FYI) has occurred in response to atmospheric and oceanic warming in the Arctic (Perovich et al, 2007; Kwok et al, 2009) With this change has come an increasing presence of melt ponds (hereafter ponds) on the ice during spring and summer, as a relative lack of topography on FYI compared to MYI promotes the spreading of ponds over a greater area (Eicken et al, 2004). Regional- and basin-scale quantification of sea ice pond properties first requires improvements to satellite retrievals (IGOS, 2007), though approaches are hindered by the subscale and spectrally variant nature of pond-covered sea ice. Thresholding, spectral unmixing, principal components analysis and artificial neural network approaches have been applied to optical data from Landsat 7 and Moderate Resolution Imaging Spectroradiometer (MODIS) scenes to derive estimates of fp from mixed pixels (Markus et al, 2003; Tschudi et al, 2008; Rösel and Kaleschke, 2011; Rösel et al, 2012).
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