Satellite microwave brightness temperature (Tb) observations over the Greenland Ice Sheet permit determination of melted/frozen snow conditions at spatial and temporal scales that are uniquely suited for climate model validation and metrics of ice sheet change. Strong microwave sensitivity to the presence of liquid water in the snowpack is clear. Yet, a host of unique microwave-derived melt products covering the ice sheet are available, each based on different methodology, and with unknown inter-product agreement. Here, we compared five different published microwave melt products over a common five-year (2003-2007) record to establish compatibility between products and agreement with in situ observations from a network of on-ice weather stations (AWS) spanning the ice sheet. A sixth product, leveraging both Tb seasonal trends and diurnal variability, was also introduced and included in the comparison. We found variable agreement between products and observations, with melt estimates based on microwave emissions modeling and the newly presented Adaptive Threshold (ADT) algorithm showing the best performance for AWS sites with more than 1-day average annual melt period (e.g., 68.9% of ADT melt days consistent with AWS observations; 31.1% of ADT frozen days contrasting with AWS observed melt). Spatial patterns of melting also varied between products. The different products showed substantial spread in melt occurrence even for products with the best AWS agreement. Product differences were generally larger under higher melt conditions; whereby, the fraction of the ice sheet experiencing ≥25 days of melting each year ranged from 4-25% for different products. While long-term satellite records have consistently shown increasing decadal trends in melt extent, our results imply that the melt frequency at any given location, particularly in the ice sheet interior where melting is less prevalent, is still subject to significant uncertainty.

中文翻译：

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比较不同卫星无源微波遥感产品在共同 5 年记录中的格陵兰冰盖融化变化

格陵兰冰盖上的卫星微波亮温 (Tb) 观测允许在空间和时间尺度上确定融化/冻结的雪状况，这特别适合气候模型验证和冰盖变化指标。对积雪中液态水存在的强烈微波敏感性是明确的。然而，有许多覆盖冰盖的独特的微波衍生的融化产品可用，每种产品都基于不同的方法，并且产品间的一致性未知。在这里，我们比较了五年 (2003-2007) 共同记录中五种不同的已发表微波融化产品，以建立产品之间的兼容性以及与跨越冰盖的冰上气象站 (AWS) 网络的现场观测结果的一致性。第六个产品，利用 Tb 季节性趋势和昼夜变化，也被引入并包括在比较中。我们发现产品和观察结果之间存在不同的一致性，基于微波发射模型和新提出的自适应阈值 (ADT) 算法的融化估计显示了具有超过 1 天平均年融化周期的 AWS 站点的最佳性能（例如，68.9% ADT 融化天数与 AWS 观察结果一致；31.1% 的 ADT 冻结天数与 AWS 观察到的融化天数形成对比）。熔化的空间模式也因产品而异。即使对于具有最佳 AWS 一致性的产品，不同的产品在熔化发生率方面也表现出很大的差异。在较高的熔体条件下，产品差异通常更大；由此，对于不同的产品，冰盖每年经历 ≥ 25 天融化的比例在 4-25% 之间。虽然长期卫星记录一直显示融化程度的年代际趋势不断增加，但我们的结果表明，任何给定位置的融化频率，特别是在融化不那么普遍的冰盖内部，仍然存在很大的不确定性。