Abstract
Abstract. Pond color, which creates the visual appearance of melt ponds on Arctic sea ice in summer, is quantitatively investigated using a two-stream radiative transfer model for ponded sea ice. The upwelling irradiance from the pond surface is determined and then its spectrum is transformed into RGB (red, green, blue) color space using a colorimetric method. The dependence of pond color on various factors such as water and ice properties and incident solar radiation is investigated. The results reveal that increasing underlying ice thickness Hi enhances both the green and blue intensities of pond color, whereas the red intensity is mostly sensitive to Hi for thin ice (Hi < 1.5 m) and to pond depth Hp for thick ice (Hi > 1.5 m), similar to the behavior of melt-pond albedo. The distribution of the incident solar spectrum F0 with wavelength affects the pond color rather than its intensity. The pond color changes from dark blue to brighter blue with increasing scattering in ice, and the influence of absorption in ice on pond color is limited. The pond color reproduced by the model agrees with field observations for Arctic sea ice in summer, which supports the validity of this study. More importantly, the pond color has been confirmed to contain information about meltwater and underlying ice, and therefore it can be used as an index to retrieve Hi and Hp. Retrievals of Hi for thin ice (Hi < 1 m) agree better with field measurements than retrievals for thick ice, but those of Hp are not good. The analysis of pond color is a new potential method to obtain thin ice thickness in summer, although more validation data and improvements to the radiative transfer model will be needed in future.
Highlights
Melt ponds are the most distinctive characteristic of the Arctic sea-ice surface during summer
A two-stream radiative transfer model was adopted and applied to ponded Arctic sea ice to examine the upwelling irradiance from the pond surface
The results reveal that both pond depth Hp and underlying ice thickness Hi have an important impact on pond color (Fig. 4)
Summary
Melt ponds are the most distinctive characteristic of the Arctic sea-ice surface during summer. Morphological studies focus on the distribution and physical properties of melt ponds using field observations and remote sensing (e.g., Huang et al, 2016). The melt-pond distribution determined by aerial photography was linked to the areally averaged surface albedo (Perovich et al, 2002b) and an obvious decrease in average surface albedo was discovered by comparing image-derived data with historical observations (Lu et al, 2010). A distinct variation trend in melt-pond fractions (MPF) in different regions of the Arctic Ocean has been found (Istomina et al, 2015) using MPF retrievals from satellite optical data (Rösel et al, 2012; Zege et al, 2015). In situ measurements of ice physics were carried out to demonstrate the mechanisms
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