Submarine groundwater discharge (SGD) represents an important component of the global water cycle. Improved assessment of SGD occurrences provides information to constrain current estimates of total freshwater discharges, which are crucial for evaluation of changes in the global water cycle.

This study leverages SGD linkages to patterns in sea surface temperature (SST) and color. Typically, groundwater temperatures exhibit less variability than SST and tend to have temperature distinct from sea water. Consequently, thermally anomalous plumes often occur in coastal areas with SGD. Nutrient-enriched groundwater flows have been linked to changes in ocean color as a consequence of algae growth and of the presence of colored dissolved organic matter. Under such conditions, SGD presence may also manifest as plumes of different colors. Changes in SST and color can be captured through satellite imagery for the thermal infrared and visible bands, which are used here to detect potential SGD (PSGD) occurrences. A method based on clustering and spectroscopy techniques is applied to automatically detect PSGD plumes. SST data are clustered to map SST anomalies. Derivative analysis and angular distance are applied to identify a color signature linked to SGD. In a novel approach, SST and color are combined to identify PSGD through remote sensing.

The methods presented in this study were applied to Landsat 7 and 8 imagery captured over southern Ireland and the west coast of the Island of Hawaiʻi, where past field surveys of radon isotopes activities and salinity have documented SGD occurrences. These selected sites are used as validation points. Derivative analysis and angular distance resulted in PSGD plumes in the vicinity of sampled locations, mainly locations with samples that are strong indicators of SGD. In general, the PSGD plumes derived from each method are compared as independent, parallel lines of evidence of PSGD occurrences. Results also show that PSGD pixels from derivative analysis and angular distance alone, without considering SST, can be obfuscated by confounding factors, such as low tides and unrelated chlorophyll enrichment, and that combining SST and color data reduces those effects. These results provide further evidence for PSGD occurrences along the south coast of Ireland and the west coast of the Island of Hawaiʻi, and showcase that satellite data can be used to better identify the location of PSGD occurrences over large areas.

海底地下水排放（SGD）是全球水循环的重要组成部分。改进对 SGD 事件的评估提供了限制当前总淡水排放量估计的信息，这对于评估全球水循环的变化至关重要。

本研究利用 SGD 与海面温度 (SST) 和颜色模式的联系。通常，地下水温度表现出比 SST 更小的变异性，并且往往具有与海水不同的温度。因此，热异常羽流经常出现在具有 SGD 的沿海地区。由于藻类生长和有色溶解有机物的存在，富含营养的地下水流与海洋颜色的变化有关。在这种情况下，SGD 的存在也可能表现为不同颜色的羽流。SST 和颜色的变化可以通过热红外和可见波段的卫星图像捕获，这些图像在这里用于检测潜在的 SGD (PSGD) 事件。一种基于聚类和光谱技术的方法被应用于自动检测 PSGD 羽流。SST 数据被聚类以映射 SST 异常。应用导数分析和角距离来识别与 SGD 相关的颜色特征。在一种新颖的方法中，将 SST 和颜色结合起来，通过遥感识别 PSGD。

本研究中提出的方法应用于在爱尔兰南部和夏威夷岛西海岸拍摄的 Landsat 7 和 8 图像，过去对氡同位素活动和盐度的实地调查记录了 SGD 的发生。这些选定的站点用作验证点。导数分析和角距离导致采样位置附近的 PSGD 羽流，主要是具有强烈指示 SGD 的样本的位置。一般来说，来自每种方法的 PSGD 羽流作为 PSGD 发生的独立、平行证据线进行比较。结果还表明，仅来自导数分析和角距离的 PSGD 像素，在不考虑 SST 的情况下，可能会被混杂因素混淆，例如低潮和不相关的叶绿素富集，并且结合 SST 和颜色数据可以减少这些影响。这些结果为爱尔兰南海岸和夏威夷岛西海岸的 PSGD 事件提供了进一步的证据，并表明卫星数据可用于更好地确定大面积 PSGD 事件的位置。