Melt ponds occupy a large fraction of the Arctic sea ice surface during spring and summer. The fraction and distribution of melt ponds have considerable impacts on Arctic climate and ecosystem by reducing the albedo. There is an urgency to obtain improved accuracy and a wider coverage of melt pond fraction (MPF) data for studying these processes. MPF information has generally been acquired from optical imagery. Conventional MPF algorithms based on high‐resolution optical sensors have treated melt ponds as features with constant reflectance; however, the spectral reflectance of ponds can vary greatly, even at a local scale. Here we use Sentinel‐2 imagery to demonstrate those previous algorithms assuming fixed melt pond‐reflectance greatly underestimate MPF. We propose a new algorithm (“LinearPolar”) based on the polar coordinate transformation that treats melt ponds as variable‐reflectance features and calculates MPF across the vector between melt pond and bare ice axes. The angular coordinate θ of the polar coordinate system, which is only associated with pond fraction rather than reflectance, is used to determinate MPF. By comparing the new algorithm and previous methods with IceBridge optical imagery data, across a variety of Sentinel‐2 images with melt ponds at various stages of development, we show that the RMSE value of the LinearPolar algorithm is about 30% lower than for the previous algorithms. Moreover, based on a sensitivity test, the new algorithm is also less sensitive to the subjective threshold for melt pond reflectance than previous algorithms.

中文翻译：

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一种基于高分辨率光学卫星图像的海冰融化池分数估算的新算法

在春季和夏季，融化池占据了北极海冰表面的很大一部分。熔池的比例和分布会通过减少反照率而对北极的气候和生态系统产生重大影响。迫切需要获得更高的准确性，并且需要对熔池分数（MPF）数据进行更广泛的研究。MPF信息通常是从光学图像中获取的。基于高分辨率光学传感器的传统MPF算法将熔池视为具有恒定反射率的特征。但是，即使在局部范围内，池塘的光谱反射率也会有很大变化。在这里，我们使用Sentinel-2图像演示那些先前的算法，假设固定的熔池反射率大大低估了MPF。我们提出了一种基于极坐标变换的新算法（“ LinearPolar”），该算法将融化池视为可变反射特征，并计算融化池与裸冰轴之间的向量的MPF。角坐标极坐标系的θ（仅与池塘比例而不是反射率相关）用于确定MPF。通过将新算法和以前的方法与IceBridge光学图像数据进行比较，在各个处于开发阶段的带有熔池的Sentinel-2图像中，我们发现LinearPolar算法的RMSE值比以前的算法低约30％算法。而且，基于敏感性测试，新算法对熔池反射率的主观阈值的敏感性也比以前的算法低。