A large part of the surface of the Greenland Ice Sheet (GrIS) and the margins of Antarctica are melting every summer, affecting their surface mass balance. Wet/dry snow status has been detected for decades using the peaks of brightness temperature at 19 GHz, and more recently at L-band (1.4 GHz) using both the SMOS and SMAP missions. SMOS owns a longer time series than SMAP with data since 2010, but the 52.5°incidence bin in the Level 3 (L3) product from Centre Aval de Traitement des Données SMOS (CATDS) that was previously used to detect melt suffers from a coarse spatial resolution. For this reason, we developed a new SMOS enhanced resolution brightness temperature (TB) product building on the radiometer version of the Scatterometter Image Reconstruction (rSIR) algorithm. We also exploited the SMOS L1C observations near 40°incidence angle instead of 52.5°as the native spatial resolution of SMOS is better at low incidence. The new product is posted on a 12.5 km polar stereographic grid and covers all the GrIS and Antarctica for 2010–2024 with twice-daily morning and afternoon acquisitions. The effective spatial resolution was evaluated to ∼30 km, a 30% enhancement compared to the SMOS L3TB at 40°and almost a 50% enhancement compared to the SMOS L3TB at 52.5°. Then, we applied a melt detection algorithm to both the enhanced resolution product at 40°and the L3TB product at 52.5°which is used in the literature. The spatial resolution enhancement results not only in the detection of smaller melt regions but also in a widespread increase in the annual number of melt days. This increase is larger than 30 days per year in the GrIS percolation area and on multiple Antarctic ice shelves. This is primarily due to the mix of dry and wet snow regions near the ice shelves grounding line, resulting in lower brightness temperature peaks in the SMOS L3TB product due to a large power spread. These findings highlight the dependence of melt detection in particular, and geophysical applications in general, on the spatial resolution of passive microwave observations. This study provides a new open dataset suitable to monitor melt at the surface and at depth on the two main ice-sheets.

中文翻译：

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SMOS 亮温分辨率增强：应用于南极和格陵兰冰盖的融化检测


格陵兰冰盖 （GrIS） 的大部分表面和南极洲的边缘每年夏天都在融化，影响了它们的表面质量平衡。几十年来，人们一直使用 19 GHz 的亮温峰值来检测湿/干雪状态，最近使用 SMOS 和 SMAP 任务在 L 波段 （1.4 GHz） 检测到湿/干雪状态。SMOS 拥有 2010 年以来的数据时间序列比 SMAP 长，但 Centre Aval de Traitement des Données SMOS （CATDS） 的 3 级 （L3） 产品中的 52.5° 入射区间以前用于检测熔体，空间分辨率较低。出于这个原因，我们开发了一种新的 SMOS 增强分辨率亮温 （TB） 产品，该产品基于辐射计版本的散射仪图像重建 （rSIR） 算法。我们还利用了 40° 入射角而不是 52.5° 附近的 SMOS L1C 观测，因为 SMOS 的原生空间分辨率在低入射角下更好。新产品张贴在 12.5 公里的极地立体网格上，覆盖 2010-2024 年的所有 GrIS 和南极洲，每天上午和下午两次采集。评估有效空间分辨率为 ∼30 公里，与 SMOS L3TB 在 40° 时相比提高了 30%，与 SMOS L3TB 在 52.5° 时相比提高了近 50%。然后，我们将熔解检测算法应用于文献中使用的 40° 的增强分辨率产品和 52.5° 的 L3TB 产品。空间分辨率的增强不仅导致检测到较小的熔化区域，而且导致每年熔化天数的广泛增加。在 GrIS 渗流区和多个南极冰架上，每年增加的天数超过 30 天。 这主要是由于冰架接地线附近干湿雪区域的混合，导致 SMOS L3TB 产品中的亮度温度峰值较低，因为功率分布较大。这些发现特别突出了熔体检测以及一般地球物理应用对被动微波观测空间分辨率的依赖性。本研究提供了一个新的开放数据集，适用于监测两个主要冰盖的表面和深度融化。