Abstract
The accurate knowledge of variations of melt ponds is important for understanding the Arctic energy budget due to its albedo–transmittance–melt feedback. In this study, we develop and validate a new method for retrieving melt pond fraction (MPF) over Arctic sea ice using all seven spectral bands of MODIS surface reflectance. We construct a robust ensemble-based deep neural network and use in-situ MPF observations collected from multiple sources as the target data to train the network. We examine the potential influence of using sea ice concentration (SIC) from different sources as additional target data (besides MPF) on the MPF retrieval. The results suggest that the inclusion of SIC has a minor impact on MPF retrieval. Based on this, we create a new MPF data from 2000 to 2019 (the longest data in our knowledge). The validation shows that our new MPF data is in good agreement with the observations. We further compare the new MPF dataset with the previously published MPF datasets. It is found that the evolution of the new MPF is similar to previous MPF data throughout the melting season, but the new MPF data is in relatively better agreement with the observations in terms of correlations and root mean squared errors (RMSE), and also has the smallest value in the first half of the melting season.
Highlights
The onset of the melting season, typically in late spring, is driven by the increase in incoming solar radiation and weather systems originating in the mid-latitudes
In the Deep neural network (DNN) training, we only considered the grids that meet the following conditions: (i) the surface reflectance in seven bands are all within the valid range; (ii) the observed melt pond fraction (MPF) is above 0 and below 100%; (iii) the observed MPF relative to the grid is smaller than the observed sea ice concentration (SIC)
We developed a new method for retrieving MPF over sea ice on the Arctic-wide scale
Summary
The onset of the melting season, typically in late spring, is driven by the increase in incoming solar radiation and weather systems originating in the mid-latitudes. As snow and ice melts, the melt water accumulates on the surface in valleys of sea ice topography. Melt ponds have lower albedo than snow and bare ice (e.g., [4,6,7,8]). This increases the absorption of solar radiation and further melts the snow and ice, leading to an important positive albedo feedback [8,9,10,11]. There are several stages of the evolution of sea ice albedo with melt ponds from May to September [4,12,13]
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